semihosting: fix accessing memory outside the bounds of the fn array

[fw/openocd] / src / target / semihosting_common.c

/***************************************************************************
 *   Copyright (C) 2018 by Liviu Ionescu                                   *
 *   <ilg@livius.net>                                                      *
 *                                                                         *
 *   Copyright (C) 2018 by Marvell Technology Group Ltd.                   *
 *   Written by Nicolas Pitre <nico@marvell.com>                           *
 *                                                                         *
 *   Copyright (C) 2010 by Spencer Oliver                                  *
 *   spen@spen-soft.co.uk                                                  *
 *                                                                         *
 *   Copyright (C) 2016 by Square, Inc.                                    *
 *   Steven Stallion <stallion@squareup.com>                               *
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 *   This program is distributed in the hope that it will be useful,       *
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
 *   GNU General Public License for more details.                          *
 *                                                                         *
 *   You should have received a copy of the GNU General Public License     *
 *   along with this program.  If not, see <http://www.gnu.org/licenses/>. *
 ***************************************************************************/

/**
 * @file
 * Common ARM semihosting support.
 *
 * Semihosting enables code running on a target to use some of the I/O
 * facilities on the host computer. The target application must be linked
 * against a library that forwards operation requests by using  an
 * instruction trapped by the debugger.
 *
 * Details can be found in
 * "Semihosting for AArch32 and AArch64, Release 2.0"
 * https://static.docs.arm.com/100863/0200/semihosting.pdf
 * from ARM Ltd.
 */

#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "target.h"
#include "target_type.h"
#include "semihosting_common.h"

#include <helper/binarybuffer.h>
#include <helper/log.h>
#include <sys/stat.h>

/**
 * It is not possible to use O_... flags defined in sys/stat.h because they
 * are not guaranteed to match the values defined by the GDB Remote Protocol.
 * See https://sourceware.org/gdb/onlinedocs/gdb/Open-Flags.html#Open-Flags
 */
enum {
        TARGET_O_RDONLY = 0x000,
        TARGET_O_WRONLY = 0x001,
        TARGET_O_RDWR   = 0x002,
        TARGET_O_APPEND = 0x008,
        TARGET_O_CREAT  = 0x200,
        TARGET_O_TRUNC  = 0x400,
        /* O_EXCL=0x800 is not required in this implementation. */
};

/* GDB remote protocol does not differentiate between text and binary open modes. */
static const int open_gdb_modeflags[12] = {
        TARGET_O_RDONLY,
        TARGET_O_RDONLY,
        TARGET_O_RDWR,
        TARGET_O_RDWR,
        TARGET_O_WRONLY | TARGET_O_CREAT | TARGET_O_TRUNC,
        TARGET_O_WRONLY | TARGET_O_CREAT | TARGET_O_TRUNC,
        TARGET_O_RDWR   | TARGET_O_CREAT | TARGET_O_TRUNC,
        TARGET_O_RDWR   | TARGET_O_CREAT | TARGET_O_TRUNC,
        TARGET_O_WRONLY | TARGET_O_CREAT | TARGET_O_APPEND,
        TARGET_O_WRONLY | TARGET_O_CREAT | TARGET_O_APPEND,
        TARGET_O_RDWR   | TARGET_O_CREAT | TARGET_O_APPEND,
        TARGET_O_RDWR   | TARGET_O_CREAT | TARGET_O_APPEND
};

static const int open_host_modeflags[12] = {
        O_RDONLY,
        O_RDONLY | O_BINARY,
        O_RDWR,
        O_RDWR   | O_BINARY,
        O_WRONLY | O_CREAT | O_TRUNC,
        O_WRONLY | O_CREAT | O_TRUNC  | O_BINARY,
        O_RDWR   | O_CREAT | O_TRUNC,
        O_RDWR   | O_CREAT | O_TRUNC  | O_BINARY,
        O_WRONLY | O_CREAT | O_APPEND,
        O_WRONLY | O_CREAT | O_APPEND | O_BINARY,
        O_RDWR   | O_CREAT | O_APPEND,
        O_RDWR   | O_CREAT | O_APPEND | O_BINARY
};

static int semihosting_common_fileio_info(struct target *target,
        struct gdb_fileio_info *fileio_info);
static int semihosting_common_fileio_end(struct target *target, int result,
        int fileio_errno, bool ctrl_c);

static int semihosting_read_fields(struct target *target, size_t number,
        uint8_t *fields);
static int semihosting_write_fields(struct target *target, size_t number,
        uint8_t *fields);
static uint64_t semihosting_get_field(struct target *target, size_t index,
        uint8_t *fields);
static void semihosting_set_field(struct target *target, uint64_t value,
        size_t index,
        uint8_t *fields);

/* Attempts to include gdb_server.h failed. */
extern int gdb_actual_connections;

/**
 * Initialize common semihosting support.
 *
 * @param target Pointer to the target to initialize.
 * @param setup
 * @param post_result
 * @return An error status if there is a problem during initialization.
 */
int semihosting_common_init(struct target *target, void *setup,
        void *post_result)
{
        LOG_DEBUG(" ");

        target->fileio_info = malloc(sizeof(*target->fileio_info));
        if (!target->fileio_info) {
                LOG_ERROR("out of memory");
                return ERROR_FAIL;
        }
        memset(target->fileio_info, 0, sizeof(*target->fileio_info));

        struct semihosting *semihosting;
        semihosting = malloc(sizeof(*target->semihosting));
        if (!semihosting) {
                LOG_ERROR("out of memory");
                return ERROR_FAIL;
        }

        semihosting->is_active = false;
        semihosting->redirect_cfg = SEMIHOSTING_REDIRECT_CFG_NONE;
        semihosting->tcp_connection = NULL;
        semihosting->stdin_fd = -1;
        semihosting->stdout_fd = -1;
        semihosting->stderr_fd = -1;
        semihosting->is_fileio = false;
        semihosting->hit_fileio = false;
        semihosting->is_resumable = false;
        semihosting->has_resumable_exit = false;
        semihosting->word_size_bytes = 0;
        semihosting->op = -1;
        semihosting->param = 0;
        semihosting->result = -1;
        semihosting->sys_errno = -1;
        semihosting->cmdline = NULL;
        semihosting->basedir = NULL;

        /* If possible, update it in setup(). */
        semihosting->setup_time = clock();

        semihosting->setup = setup;
        semihosting->post_result = post_result;

        target->semihosting = semihosting;

        target->type->get_gdb_fileio_info = semihosting_common_fileio_info;
        target->type->gdb_fileio_end = semihosting_common_fileio_end;

        return ERROR_OK;
}

struct semihosting_tcp_service {
        struct semihosting *semihosting;
        char *name;
        int error;
};

static bool semihosting_is_redirected(struct semihosting *semihosting, int fd)
{
        if (semihosting->redirect_cfg == SEMIHOSTING_REDIRECT_CFG_NONE)
                return false;

        bool is_read_op = false;

        switch (semihosting->op) {
        /* check debug semihosting operations: READC, WRITEC and WRITE0 */
        case SEMIHOSTING_SYS_READC:
                is_read_op = true;
                /* fall through */
        case SEMIHOSTING_SYS_WRITEC:
        case SEMIHOSTING_SYS_WRITE0:
                /* debug operations are redirected when CFG is either DEBUG or ALL */
                if (semihosting->redirect_cfg == SEMIHOSTING_REDIRECT_CFG_STDIO)
                        return false;
                break;

        /* check stdio semihosting operations: READ and WRITE */
        case SEMIHOSTING_SYS_READ:
                is_read_op = true;
                /* fall through */
        case SEMIHOSTING_SYS_WRITE:
                /* stdio operations are redirected when CFG is either STDIO or ALL */
                if (semihosting->redirect_cfg == SEMIHOSTING_REDIRECT_CFG_DEBUG)
                        return false;
                break;

        default:
                return false;
        }

        if (is_read_op)
                return fd == semihosting->stdin_fd;

        /* write operation */
        return fd == semihosting->stdout_fd || fd == semihosting->stderr_fd;
}

static ssize_t semihosting_redirect_write(struct semihosting *semihosting, void *buf, int size)
{
        if (!semihosting->tcp_connection) {
                LOG_ERROR("No connected TCP client for semihosting");
                semihosting->sys_errno = EBADF; /* Bad file number */
                return -1;
        }

        struct semihosting_tcp_service *service = semihosting->tcp_connection->service->priv;

        int retval = connection_write(semihosting->tcp_connection, buf, size);

        if (retval < 0)
                log_socket_error(service->name);

        return retval;
}

static ssize_t semihosting_write(struct semihosting *semihosting, int fd, void *buf, int size)
{
        if (semihosting_is_redirected(semihosting, fd))
                return semihosting_redirect_write(semihosting, buf, size);

        /* default write */
        return write(fd, buf, size);
}

static ssize_t semihosting_redirect_read(struct semihosting *semihosting, void *buf, int size)
{
        if (!semihosting->tcp_connection) {
                LOG_ERROR("No connected TCP client for semihosting");
                semihosting->sys_errno = EBADF; /* Bad file number */
                return -1;
        }

        struct semihosting_tcp_service *service = semihosting->tcp_connection->service->priv;

        service->error = ERROR_OK;
        semihosting->tcp_connection->input_pending = true;

        int retval = connection_read(semihosting->tcp_connection, buf, size);

        if (retval <= 0)
                service->error = ERROR_SERVER_REMOTE_CLOSED;

        if (retval < 0)
                log_socket_error(service->name);

        semihosting->tcp_connection->input_pending = false;

        return retval;
}

static inline int semihosting_putchar(struct semihosting *semihosting, int fd, int c)
{
        if (semihosting_is_redirected(semihosting, fd))
                return semihosting_redirect_write(semihosting, &c, 1);

        /* default putchar */
        return putchar(c);
}

static inline ssize_t semihosting_read(struct semihosting *semihosting, int fd, void *buf, int size)
{
        if (semihosting_is_redirected(semihosting, fd))
                return semihosting_redirect_read(semihosting, buf, size);

        /* default read */
        ssize_t result = read(fd, buf, size);
        semihosting->sys_errno = errno;

        return result;
}

static inline int semihosting_getchar(struct semihosting *semihosting, int fd)
{
        if (semihosting_is_redirected(semihosting, fd)) {
                unsigned char c;

                if (semihosting_redirect_read(semihosting, &c, 1) > 0)
                        return c;

                return EOF;
        }

        /* default getchar */
        return getchar();
}

/**
 * User operation parameter string storage buffer. Contains valid data when the
 * TARGET_EVENT_SEMIHOSTING_USER_CMD_xxxxx event callbacks are running.
 */
static char *semihosting_user_op_params;

/**
 * Portable implementation of ARM semihosting calls.
 * Performs the currently pending semihosting operation
 * encoded in target->semihosting.
 */
int semihosting_common(struct target *target)
{
        struct semihosting *semihosting = target->semihosting;
        if (!semihosting) {
                /* Silently ignore if the semihosting field was not set. */
                return ERROR_OK;
        }

        struct gdb_fileio_info *fileio_info = target->fileio_info;

        /*
         * By default return an error.
         * The actual result must be set by each function
         */
        semihosting->result = -1;

        /* Most operations are resumable, except the two exit calls. */
        semihosting->is_resumable = true;

        int retval;

        /* Enough space to hold 4 long words. */
        uint8_t fields[4*8];

        LOG_DEBUG("op=0x%x, param=0x%" PRIx64, semihosting->op,
                semihosting->param);

        switch (semihosting->op) {

                case SEMIHOSTING_SYS_CLOCK:     /* 0x10 */
                        /*
                         * Returns the number of centiseconds (hundredths of a second)
                         * since the execution started.
                         *
                         * Values returned can be of limited use for some benchmarking
                         * purposes because of communication overhead or other
                         * agent-specific factors. For example, with a debug hardware
                         * unit the request is passed back to the host for execution.
                         * This can lead to unpredictable delays in transmission and
                         * process scheduling.
                         *
                         * Use this function to calculate time intervals, by calculating
                         * differences between intervals with and without the code
                         * sequence to be timed.
                         *
                         * Entry
                         * The PARAMETER REGISTER must contain 0. There are no other
                         * parameters.
                         *
                         * Return
                         * On exit, the RETURN REGISTER contains:
                         * - The number of centiseconds since some arbitrary start
                         * point, if the call is successful.
                         * - –1 if the call is not successful. For example, because
                         * of a communications error.
                         */
                {
                        clock_t delta = clock() - semihosting->setup_time;

                        semihosting->result = delta / (CLOCKS_PER_SEC / 100);
                }
                break;

                case SEMIHOSTING_SYS_CLOSE:     /* 0x02 */
                        /*
                         * Closes a file on the host system. The handle must reference
                         * a file that was opened with SYS_OPEN.
                         *
                         * Entry
                         * On entry, the PARAMETER REGISTER contains a pointer to a
                         * one-field argument block:
                         * - field 1 Contains a handle for an open file.
                         *
                         * Return
                         * On exit, the RETURN REGISTER contains:
                         * - 0 if the call is successful
                         * - –1 if the call is not successful.
                         */
                        retval = semihosting_read_fields(target, 1, fields);
                        if (retval != ERROR_OK)
                                return retval;
                        else {
                                int fd = semihosting_get_field(target, 0, fields);
                                /* Do not allow to close OpenOCD's own standard streams */
                                if (fd == 0 || fd == 1 || fd == 2) {
                                        LOG_DEBUG("ignoring semihosting attempt to close %s",
                                                        (fd == 0) ? "stdin" :
                                                        (fd == 1) ? "stdout" : "stderr");
                                        /* Just pretend success */
                                        if (semihosting->is_fileio) {
                                                semihosting->result = 0;
                                        } else {
                                                semihosting->result = 0;
                                                semihosting->sys_errno = 0;
                                        }
                                        break;
                                }
                                /* Close the descriptor */
                                if (semihosting->is_fileio) {
                                        semihosting->hit_fileio = true;
                                        fileio_info->identifier = "close";
                                        fileio_info->param_1 = fd;
                                } else {
                                        semihosting->result = close(fd);
                                        semihosting->sys_errno = errno;
                                        LOG_DEBUG("close(%d)=%d", fd, (int)semihosting->result);
                                }
                        }
                        break;

                case SEMIHOSTING_SYS_ERRNO:     /* 0x13 */
                        /*
                         * Returns the value of the C library errno variable that is
                         * associated with the semihosting implementation. The errno
                         * variable can be set by a number of C library semihosted
                         * functions, including:
                         * - SYS_REMOVE
                         * - SYS_OPEN
                         * - SYS_CLOSE
                         * - SYS_READ
                         * - SYS_WRITE
                         * - SYS_SEEK.
                         *
                         * Whether errno is set or not, and to what value, is entirely
                         * host-specific, except where the ISO C standard defines the
                         * behavior.
                         *
                         * Entry
                         * There are no parameters. The PARAMETER REGISTER must be 0.
                         *
                         * Return
                         * On exit, the RETURN REGISTER contains the value of the C
                         * library errno variable.
                         */
                        semihosting->result = semihosting->sys_errno;
                        break;

                case SEMIHOSTING_SYS_EXIT:      /* 0x18 */
                        /*
                         * Note: SYS_EXIT was called angel_SWIreason_ReportException in
                         * previous versions of the documentation.
                         *
                         * An application calls this operation to report an exception
                         * to the debugger directly. The most common use is to report
                         * that execution has completed, using ADP_Stopped_ApplicationExit.
                         *
                         * Note: This semihosting operation provides no means for 32-bit
                         * callers to indicate an application exit with a specified exit
                         * code. Semihosting callers may prefer to check for the presence
                         * of the SH_EXT_EXTENDED_REPORT_EXCEPTION extension and use
                         * the SYS_REPORT_EXCEPTION_EXTENDED operation instead, if it
                         * is available.
                         *
                         * Entry (32-bit)
                         * On entry, the PARAMETER register is set to a reason code
                         * describing the cause of the trap. Not all semihosting client
                         * implementations will necessarily trap every corresponding
                         * event. Important reason codes are:
                         *
                         * - ADP_Stopped_ApplicationExit 0x20026
                         * - ADP_Stopped_RunTimeErrorUnknown 0x20023
                         *
                         * Entry (64-bit)
                         * On entry, the PARAMETER REGISTER contains a pointer to a
                         * two-field argument block:
                         * - field 1 The exception type, which is one of the set of
                         * reason codes in the above tables.
                         * - field 2 A subcode, whose meaning depends on the reason
                         * code in field 1.
                         * In particular, if field 1 is ADP_Stopped_ApplicationExit
                         * then field 2 is an exit status code, as passed to the C
                         * standard library exit() function. A simulator receiving
                         * this request must notify a connected debugger, if present,
                         * and then exit with the specified status.
                         *
                         * Return
                         * No return is expected from these calls. However, it is
                         * possible for the debugger to request that the application
                         * continues by performing an RDI_Execute request or equivalent.
                         * In this case, execution continues with the registers as they
                         * were on entry to the operation, or as subsequently modified
                         * by the debugger.
                         */
                        if (semihosting->word_size_bytes == 8) {
                                retval = semihosting_read_fields(target, 2, fields);
                                if (retval != ERROR_OK)
                                        return retval;
                                else {
                                        int type = semihosting_get_field(target, 0, fields);
                                        int code = semihosting_get_field(target, 1, fields);

                                        if (type == ADP_STOPPED_APPLICATION_EXIT) {
                                                if (!gdb_actual_connections)
                                                        exit(code);
                                                else {
                                                        fprintf(stderr,
                                                                "semihosting: *** application exited with %d ***\n",
                                                                code);
                                                }
                                        } else {
                                                fprintf(stderr,
                                                        "semihosting: application exception %#x\n",
                                                        type);
                                        }
                                }
                        } else {
                                if (semihosting->param == ADP_STOPPED_APPLICATION_EXIT) {
                                        if (!gdb_actual_connections)
                                                exit(0);
                                        else {
                                                fprintf(stderr,
                                                        "semihosting: *** application exited normally ***\n");
                                        }
                                } else if (semihosting->param == ADP_STOPPED_RUN_TIME_ERROR) {
                                        /* Chosen more or less arbitrarily to have a nicer message,
                                         * otherwise all other return the same exit code 1. */
                                        if (!gdb_actual_connections)
                                                exit(1);
                                        else {
                                                fprintf(stderr,
                                                        "semihosting: *** application exited with error ***\n");
                                        }
                                } else {
                                        if (!gdb_actual_connections)
                                                exit(1);
                                        else {
                                                fprintf(stderr,
                                                        "semihosting: application exception %#x\n",
                                                        (unsigned) semihosting->param);
                                        }
                                }
                        }
                        if (!semihosting->has_resumable_exit) {
                                semihosting->is_resumable = false;
                                return target_call_event_callbacks(target, TARGET_EVENT_HALTED);
                        }
                        break;

                case SEMIHOSTING_SYS_EXIT_EXTENDED:     /* 0x20 */
                        /*
                         * This operation is only supported if the semihosting extension
                         * SH_EXT_EXIT_EXTENDED is implemented. SH_EXT_EXIT_EXTENDED is
                         * reported using feature byte 0, bit 0. If this extension is
                         * supported, then the implementation provides a means to
                         * report a normal exit with a nonzero exit status in both 32-bit
                         * and 64-bit semihosting APIs.
                         *
                         * The implementation must provide the semihosting call
                         * SYS_EXIT_EXTENDED for both A64 and A32/T32 semihosting APIs.
                         *
                         * SYS_EXIT_EXTENDED is used by an application to report an
                         * exception or exit to the debugger directly. The most common
                         * use is to report that execution has completed, using
                         * ADP_Stopped_ApplicationExit.
                         *
                         * Entry
                         * On entry, the PARAMETER REGISTER contains a pointer to a
                         * two-field argument block:
                         * - field 1 The exception type, which should be one of the set
                         * of reason codes that are documented for the SYS_EXIT
                         * (0x18) call. For example, ADP_Stopped_ApplicationExit.
                         * - field 2 A subcode, whose meaning depends on the reason
                         * code in field 1. In particular, if field 1 is
                         * ADP_Stopped_ApplicationExit then field 2 is an exit status
                         * code, as passed to the C standard library exit() function.
                         * A simulator receiving this request must notify a connected
                         * debugger, if present, and then exit with the specified status.
                         *
                         * Return
                         * No return is expected from these calls.
                         *
                         * For the A64 API, this call is identical to the behavior of
                         * the mandatory SYS_EXIT (0x18) call. If this extension is
                         * supported, then both calls must be implemented.
                         */
                        retval = semihosting_read_fields(target, 2, fields);
                        if (retval != ERROR_OK)
                                return retval;
                        else {
                                int type = semihosting_get_field(target, 0, fields);
                                int code = semihosting_get_field(target, 1, fields);

                                if (type == ADP_STOPPED_APPLICATION_EXIT) {
                                        if (!gdb_actual_connections)
                                                exit(code);
                                        else {
                                                fprintf(stderr,
                                                        "semihosting: *** application exited with %d ***\n",
                                                        code);
                                        }
                                } else {
                                        fprintf(stderr, "semihosting: exception %#x\n",
                                                type);
                                }
                        }
                        if (!semihosting->has_resumable_exit) {
                                semihosting->is_resumable = false;
                                return target_call_event_callbacks(target, TARGET_EVENT_HALTED);
                        }
                        break;

                case SEMIHOSTING_SYS_FLEN:      /* 0x0C */
                        /*
                         * Returns the length of a specified file.
                         *
                         * Entry
                         * On entry, the PARAMETER REGISTER contains a pointer to a
                         * one-field argument block:
                         * - field 1 A handle for a previously opened, seekable file
                         * object.
                         *
                         * Return
                         * On exit, the RETURN REGISTER contains:
                         * - The current length of the file object, if the call is
                         * successful.
                         * - –1 if an error occurs.
                         */
                        if (semihosting->is_fileio) {
                                semihosting->result = -1;
                                semihosting->sys_errno = EINVAL;
                        }
                        retval = semihosting_read_fields(target, 1, fields);
                        if (retval != ERROR_OK)
                                return retval;
                        else {
                                int fd = semihosting_get_field(target, 0, fields);
                                struct stat buf;
                                semihosting->result = fstat(fd, &buf);
                                if (semihosting->result == -1) {
                                        semihosting->sys_errno = errno;
                                        LOG_DEBUG("fstat(%d)=%d", fd, (int)semihosting->result);
                                        break;
                                }
                                LOG_DEBUG("fstat(%d)=%d", fd, (int)semihosting->result);
                                semihosting->result = buf.st_size;
                        }
                        break;

                case SEMIHOSTING_SYS_GET_CMDLINE:       /* 0x15 */
                        /*
                         * Returns the command line that is used for the call to the
                         * executable, that is, argc and argv.
                         *
                         * Entry
                         * On entry, the PARAMETER REGISTER points to a two-field data
                         * block to be used for returning the command string and its length:
                         * - field 1 A pointer to a buffer of at least the size that is
                         * specified in field 2.
                         * - field 2 The length of the buffer in bytes.
                         *
                         * Return
                         * On exit:
                         * If the call is successful, then the RETURN REGISTER contains 0,
                         * the PARAMETER REGISTER is unchanged, and the data block is
                         * updated as follows:
                         * - field 1 A pointer to a null-terminated string of the command
                         * line.
                         * - field 2 The length of the string in bytes.
                         * If the call is not successful, then the RETURN REGISTER
                         * contains -1.
                         *
                         * Note: The semihosting implementation might impose limits on
                         * the maximum length of the string that can be transferred.
                         * However, the implementation must be able to support a
                         * command-line length of at least 80 bytes.
                         */
                        retval = semihosting_read_fields(target, 2, fields);
                        if (retval != ERROR_OK)
                                return retval;
                        else {
                                uint64_t addr = semihosting_get_field(target, 0, fields);
                                size_t size = semihosting_get_field(target, 1, fields);

                                char *arg = semihosting->cmdline ?
                                        semihosting->cmdline : "";
                                uint32_t len = strlen(arg) + 1;
                                if (len > size)
                                        semihosting->result = -1;
                                else {
                                        semihosting_set_field(target, len, 1, fields);
                                        retval = target_write_buffer(target, addr, len,
                                                        (uint8_t *)arg);
                                        if (retval != ERROR_OK)
                                                return retval;
                                        semihosting->result = 0;

                                        retval = semihosting_write_fields(target, 2, fields);
                                        if (retval != ERROR_OK)
                                                return retval;
                                }
                                LOG_DEBUG("SYS_GET_CMDLINE=[%s],%d", arg,
                                        (int)semihosting->result);
                        }
                        break;

                case SEMIHOSTING_SYS_HEAPINFO:  /* 0x16 */
                        /*
                         * Returns the system stack and heap parameters.
                         *
                         * Entry
                         * On entry, the PARAMETER REGISTER contains the address of a
                         * pointer to a four-field data block. The contents of the data
                         * block are filled by the function. The following C-like
                         * pseudocode describes the layout of the block:
                         * struct block {
                         *   void* heap_base;
                         *   void* heap_limit;
                         *   void* stack_base;
                         *   void* stack_limit;
                         * };
                         *
                         * Return
                         * On exit, the PARAMETER REGISTER is unchanged and the data
                         * block has been updated.
                         */
                        retval = semihosting_read_fields(target, 1, fields);
                        if (retval != ERROR_OK)
                                return retval;
                        else {
                                uint64_t addr = semihosting_get_field(target, 0, fields);
                                /* tell the remote we have no idea */
                                memset(fields, 0, 4 * semihosting->word_size_bytes);
                                retval = target_write_memory(target, addr, 4,
                                                semihosting->word_size_bytes,
                                                fields);
                                if (retval != ERROR_OK)
                                        return retval;
                                semihosting->result = 0;
                        }
                        break;

                case SEMIHOSTING_SYS_ISERROR:   /* 0x08 */
                        /*
                         * Determines whether the return code from another semihosting
                         * call is an error status or not.
                         *
                         * This call is passed a parameter block containing the error
                         * code to examine.
                         *
                         * Entry
                         * On entry, the PARAMETER REGISTER contains a pointer to a
                         * one-field data block:
                         * - field 1 The required status word to check.
                         *
                         * Return
                         * On exit, the RETURN REGISTER contains:
                         * - 0 if the status field is not an error indication
                         * - A nonzero value if the status field is an error indication.
                         */
                        retval = semihosting_read_fields(target, 1, fields);
                        if (retval != ERROR_OK)
                                return retval;

                        uint64_t code = semihosting_get_field(target, 0, fields);
                        semihosting->result = (code != 0);
                        break;

                case SEMIHOSTING_SYS_ISTTY:     /* 0x09 */
                        /*
                         * Checks whether a file is connected to an interactive device.
                         *
                         * Entry
                         * On entry, the PARAMETER REGISTER contains a pointer to a
                         * one-field argument block:
                         * field 1 A handle for a previously opened file object.
                         *
                         * Return
                         * On exit, the RETURN REGISTER contains:
                         * - 1 if the handle identifies an interactive device.
                         * - 0 if the handle identifies a file.
                         * - A value other than 1 or 0 if an error occurs.
                         */
                        if (semihosting->is_fileio) {
                                semihosting->hit_fileio = true;
                                fileio_info->identifier = "isatty";
                                fileio_info->param_1 = semihosting->param;
                        } else {
                                retval = semihosting_read_fields(target, 1, fields);
                                if (retval != ERROR_OK)
                                        return retval;
                                int fd = semihosting_get_field(target, 0, fields);
                                semihosting->result = isatty(fd);
                                semihosting->sys_errno = errno;
                                LOG_DEBUG("isatty(%d)=%d", fd, (int)semihosting->result);
                        }
                        break;

                case SEMIHOSTING_SYS_OPEN:      /* 0x01 */
                        /*
                         * Opens a file on the host system.
                         *
                         * The file path is specified either as relative to the current
                         * directory of the host process, or absolute, using the path
                         * conventions of the host operating system.
                         *
                         * Semihosting implementations must support opening the special
                         * path name :semihosting-features as part of the semihosting
                         * extensions reporting mechanism.
                         *
                         * ARM targets interpret the special path name :tt as meaning
                         * the console input stream, for an open-read or the console
                         * output stream, for an open-write. Opening these streams is
                         * performed as part of the standard startup code for those
                         * applications that reference the C stdio streams. The
                         * semihosting extension SH_EXT_STDOUT_STDERR allows the
                         * semihosting caller to open separate output streams
                         * corresponding to stdout and stderr. This extension is
                         * reported using feature byte 0, bit 1. Use SYS_OPEN with
                         * the special path name :semihosting-features to access the
                         * feature bits.
                         *
                         * If this extension is supported, the implementation must
                         * support the following additional semantics to SYS_OPEN:
                         * - If the special path name :tt is opened with an fopen
                         * mode requesting write access (w, wb, w+, or w+b), then
                         * this is a request to open stdout.
                         * - If the special path name :tt is opened with a mode
                         * requesting append access (a, ab, a+, or a+b), then this is
                         * a request to open stderr.
                         *
                         * Entry
                         * On entry, the PARAMETER REGISTER contains a pointer to a
                         * three-field argument block:
                         * - field 1 A pointer to a null-terminated string containing
                         * a file or device name.
                         * - field 2 An integer that specifies the file opening mode.
                         * - field 3 An integer that gives the length of the string
                         * pointed to by field 1.
                         *
                         * The length does not include the terminating null character
                         * that must be present.
                         *
                         * Return
                         * On exit, the RETURN REGISTER contains:
                         * - A nonzero handle if the call is successful.
                         * - –1 if the call is not successful.
                         */
                        retval = semihosting_read_fields(target, 3, fields);
                        if (retval != ERROR_OK)
                                return retval;
                        else {
                                uint64_t addr = semihosting_get_field(target, 0, fields);
                                uint32_t mode = semihosting_get_field(target, 1, fields);
                                size_t len = semihosting_get_field(target, 2, fields);

                                if (mode > 11) {
                                        semihosting->result = -1;
                                        semihosting->sys_errno = EINVAL;
                                        break;
                                }
                                size_t basedir_len = semihosting->basedir ? strlen(semihosting->basedir) : 0;
                                uint8_t *fn = malloc(basedir_len + len + 2);
                                if (!fn) {
                                        semihosting->result = -1;
                                        semihosting->sys_errno = ENOMEM;
                                } else {
                                        if (basedir_len > 0) {
                                                strcpy((char *)fn, semihosting->basedir);
                                                if (fn[basedir_len - 1] != '/')
                                                        fn[basedir_len++] = '/';
                                        }
                                        retval = target_read_memory(target, addr, 1, len, fn + basedir_len);
                                        if (retval != ERROR_OK) {
                                                free(fn);
                                                return retval;
                                        }
                                        fn[basedir_len + len] = 0;
                                        /* TODO: implement the :semihosting-features special file.
                                         * */
                                        if (semihosting->is_fileio) {
                                                if (strcmp((char *)fn, ":semihosting-features") == 0) {
                                                        semihosting->result = -1;
                                                        semihosting->sys_errno = EINVAL;
                                                } else if (strcmp((char *)fn, ":tt") == 0) {
                                                        if (mode == 0)
                                                                semihosting->result = 0;
                                                        else if (mode == 4)
                                                                semihosting->result = 1;
                                                        else if (mode == 8)
                                                                semihosting->result = 2;
                                                        else
                                                                semihosting->result = -1;
                                                } else {
                                                        semihosting->hit_fileio = true;
                                                        fileio_info->identifier = "open";
                                                        fileio_info->param_1 = addr;
                                                        fileio_info->param_2 = len;
                                                        fileio_info->param_3 = open_gdb_modeflags[mode];
                                                        fileio_info->param_4 = 0644;
                                                }
                                        } else {
                                                if (strcmp((char *)fn, ":tt") == 0) {
                                                        /* Mode is:
                                                         * - 0-3 ("r") for stdin,
                                                         * - 4-7 ("w") for stdout,
                                                         * - 8-11 ("a") for stderr */
                                                        if (mode < 4) {
                                                                int fd = dup(STDIN_FILENO);
                                                                semihosting->result = fd;
                                                                semihosting->stdin_fd = fd;
                                                                semihosting->sys_errno = errno;
                                                                LOG_DEBUG("dup(STDIN)=%d",
                                                                        (int)semihosting->result);
                                                        } else if (mode < 8) {
                                                                int fd = dup(STDOUT_FILENO);
                                                                semihosting->result = fd;
                                                                semihosting->stdout_fd = fd;
                                                                semihosting->sys_errno = errno;
                                                                LOG_DEBUG("dup(STDOUT)=%d",
                                                                        (int)semihosting->result);
                                                        } else {
                                                                int fd = dup(STDERR_FILENO);
                                                                semihosting->result = fd;
                                                                semihosting->stderr_fd = fd;
                                                                semihosting->sys_errno = errno;
                                                                LOG_DEBUG("dup(STDERR)=%d",
                                                                        (int)semihosting->result);
                                                        }
                                                } else {
                                                        /* cygwin requires the permission setting
                                                         * otherwise it will fail to reopen a previously
                                                         * written file */
                                                        semihosting->result = open((char *)fn,
                                                                        open_host_modeflags[mode],
                                                                        0644);
                                                        semihosting->sys_errno = errno;
                                                        LOG_DEBUG("open('%s')=%d", fn,
                                                                (int)semihosting->result);
                                                }
                                        }
                                        free(fn);
                                }
                        }
                        break;

                case SEMIHOSTING_SYS_READ:      /* 0x06 */
                        /*
                         * Reads the contents of a file into a buffer. The file position
                         * is specified either:
                         * - Explicitly by a SYS_SEEK.
                         * - Implicitly one byte beyond the previous SYS_READ or
                         * SYS_WRITE request.
                         *
                         * The file position is at the start of the file when it is
                         * opened, and is lost when the file is closed. Perform the
                         * file operation as a single action whenever possible. For
                         * example, do not split a read of 16KB into four 4KB chunks
                         * unless there is no alternative.
                         *
                         * Entry
                         * On entry, the PARAMETER REGISTER contains a pointer to a
                         * three-field data block:
                         * - field 1 Contains a handle for a file previously opened
                         * with SYS_OPEN.
                         * - field 2 Points to a buffer.
                         * - field 3 Contains the number of bytes to read to the buffer
                         * from the file.
                         *
                         * Return
                         * On exit, the RETURN REGISTER contains the number of bytes not
                         * filled in the buffer (buffer_length - bytes_read) as follows:
                         * - If the RETURN REGISTER is 0, the entire buffer was
                         * successfully filled.
                         * - If the RETURN REGISTER is the same as field 3, no bytes
                         * were read (EOF can be assumed).
                         * - If the RETURN REGISTER contains a value smaller than
                         * field 3, the read succeeded but the buffer was only partly
                         * filled. For interactive devices, this is the most common
                         * return value.
                         */
                        retval = semihosting_read_fields(target, 3, fields);
                        if (retval != ERROR_OK)
                                return retval;
                        else {
                                int fd = semihosting_get_field(target, 0, fields);
                                uint64_t addr = semihosting_get_field(target, 1, fields);
                                size_t len = semihosting_get_field(target, 2, fields);
                                if (semihosting->is_fileio) {
                                        semihosting->hit_fileio = true;
                                        fileio_info->identifier = "read";
                                        fileio_info->param_1 = fd;
                                        fileio_info->param_2 = addr;
                                        fileio_info->param_3 = len;
                                } else {
                                        uint8_t *buf = malloc(len);
                                        if (!buf) {
                                                semihosting->result = -1;
                                                semihosting->sys_errno = ENOMEM;
                                        } else {
                                                semihosting->result = semihosting_read(semihosting, fd, buf, len);
                                                LOG_DEBUG("read(%d, 0x%" PRIx64 ", %zu)=%d",
                                                        fd,
                                                        addr,
                                                        len,
                                                        (int)semihosting->result);
                                                if (semihosting->result >= 0) {
                                                        retval = target_write_buffer(target, addr,
                                                                        semihosting->result,
                                                                        buf);
                                                        if (retval != ERROR_OK) {
                                                                free(buf);
                                                                return retval;
                                                        }
                                                        /* the number of bytes NOT filled in */
                                                        semihosting->result = len -
                                                                semihosting->result;
                                                }
                                                free(buf);
                                        }
                                }
                        }
                        break;

                case SEMIHOSTING_SYS_READC:     /* 0x07 */
                        /*
                         * Reads a byte from the console.
                         *
                         * Entry
                         * The PARAMETER REGISTER must contain 0. There are no other
                         * parameters or values possible.
                         *
                         * Return
                         * On exit, the RETURN REGISTER contains the byte read from
                         * the console.
                         */
                        if (semihosting->is_fileio) {
                                LOG_ERROR("SYS_READC not supported by semihosting fileio");
                                return ERROR_FAIL;
                        }
                        semihosting->result = semihosting_getchar(semihosting, semihosting->stdin_fd);
                        LOG_DEBUG("getchar()=%d", (int)semihosting->result);
                        break;

                case SEMIHOSTING_SYS_REMOVE:    /* 0x0E */
                        /*
                         * Deletes a specified file on the host filing system.
                         *
                         * Entry
                         * On entry, the PARAMETER REGISTER contains a pointer to a
                         * two-field argument block:
                         * - field 1 Points to a null-terminated string that gives the
                         * path name of the file to be deleted.
                         * - field 2 The length of the string.
                         *
                         * Return
                         * On exit, the RETURN REGISTER contains:
                         * - 0 if the delete is successful
                         * - A nonzero, host-specific error code if the delete fails.
                         */
                        retval = semihosting_read_fields(target, 2, fields);
                        if (retval != ERROR_OK)
                                return retval;
                        else {
                                uint64_t addr = semihosting_get_field(target, 0, fields);
                                size_t len = semihosting_get_field(target, 1, fields);
                                if (semihosting->is_fileio) {
                                        semihosting->hit_fileio = true;
                                        fileio_info->identifier = "unlink";
                                        fileio_info->param_1 = addr;
                                        fileio_info->param_2 = len;
                                } else {
                                        uint8_t *fn = malloc(len+1);
                                        if (!fn) {
                                                semihosting->result = -1;
                                                semihosting->sys_errno = ENOMEM;
                                        } else {
                                                retval =
                                                        target_read_memory(target, addr, 1, len,
                                                                fn);
                                                if (retval != ERROR_OK) {
                                                        free(fn);
                                                        return retval;
                                                }
                                                fn[len] = 0;
                                                semihosting->result = remove((char *)fn);
                                                semihosting->sys_errno = errno;
                                                LOG_DEBUG("remove('%s')=%d", fn,
                                                        (int)semihosting->result);

                                                free(fn);
                                        }
                                }
                        }
                        break;

                case SEMIHOSTING_SYS_RENAME:    /* 0x0F */
                        /*
                         * Renames a specified file.
                         *
                         * Entry
                         * On entry, the PARAMETER REGISTER contains a pointer to a
                         * four-field data block:
                         * - field 1 A pointer to the name of the old file.
                         * - field 2 The length of the old filename.
                         * - field 3 A pointer to the new filename.
                         * - field 4 The length of the new filename. Both strings are
                         * null-terminated.
                         *
                         * Return
                         * On exit, the RETURN REGISTER contains:
                         * - 0 if the rename is successful.
                         * - A nonzero, host-specific error code if the rename fails.
                         */
                        retval = semihosting_read_fields(target, 4, fields);
                        if (retval != ERROR_OK)
                                return retval;
                        else {
                                uint64_t addr1 = semihosting_get_field(target, 0, fields);
                                size_t len1 = semihosting_get_field(target, 1, fields);
                                uint64_t addr2 = semihosting_get_field(target, 2, fields);
                                size_t len2 = semihosting_get_field(target, 3, fields);
                                if (semihosting->is_fileio) {
                                        semihosting->hit_fileio = true;
                                        fileio_info->identifier = "rename";
                                        fileio_info->param_1 = addr1;
                                        fileio_info->param_2 = len1;
                                        fileio_info->param_3 = addr2;
                                        fileio_info->param_4 = len2;
                                } else {
                                        uint8_t *fn1 = malloc(len1+1);
                                        uint8_t *fn2 = malloc(len2+1);
                                        if (!fn1 || !fn2) {
                                                free(fn1);
                                                free(fn2);
                                                semihosting->result = -1;
                                                semihosting->sys_errno = ENOMEM;
                                        } else {
                                                retval = target_read_memory(target, addr1, 1, len1,
                                                                fn1);
                                                if (retval != ERROR_OK) {
                                                        free(fn1);
                                                        free(fn2);
                                                        return retval;
                                                }
                                                retval = target_read_memory(target, addr2, 1, len2,
                                                                fn2);
                                                if (retval != ERROR_OK) {
                                                        free(fn1);
                                                        free(fn2);
                                                        return retval;
                                                }
                                                fn1[len1] = 0;
                                                fn2[len2] = 0;
                                                semihosting->result = rename((char *)fn1,
                                                                (char *)fn2);
                                                semihosting->sys_errno = errno;
                                                LOG_DEBUG("rename('%s', '%s')=%d", fn1, fn2,
                                                        (int)semihosting->result);

                                                free(fn1);
                                                free(fn2);
                                        }
                                }
                        }
                        break;

                case SEMIHOSTING_SYS_SEEK:      /* 0x0A */
                        /*
                         * Seeks to a specified position in a file using an offset
                         * specified from the start of the file. The file is assumed
                         * to be a byte array and the offset is given in bytes.
                         *
                         * Entry
                         * On entry, the PARAMETER REGISTER contains a pointer to a
                         * two-field data block:
                         * - field 1 A handle for a seekable file object.
                         * - field 2 The absolute byte position to seek to.
                         *
                         * Return
                         * On exit, the RETURN REGISTER contains:
                         * - 0 if the request is successful.
                         * - A negative value if the request is not successful.
                         * Use SYS_ERRNO to read the value of the host errno variable
                         * describing the error.
                         *
                         * Note: The effect of seeking outside the current extent of
                         * the file object is undefined.
                         */
                        retval = semihosting_read_fields(target, 2, fields);
                        if (retval != ERROR_OK)
                                return retval;
                        else {
                                int fd = semihosting_get_field(target, 0, fields);
                                off_t pos = semihosting_get_field(target, 1, fields);
                                if (semihosting->is_fileio) {
                                        semihosting->hit_fileio = true;
                                        fileio_info->identifier = "lseek";
                                        fileio_info->param_1 = fd;
                                        fileio_info->param_2 = pos;
                                        fileio_info->param_3 = SEEK_SET;
                                } else {
                                        semihosting->result = lseek(fd, pos, SEEK_SET);
                                        semihosting->sys_errno = errno;
                                        LOG_DEBUG("lseek(%d, %d)=%d", fd, (int)pos,
                                                (int)semihosting->result);
                                        if (semihosting->result == pos)
                                                semihosting->result = 0;
                                }
                        }
                        break;

                case SEMIHOSTING_SYS_SYSTEM:    /* 0x12 */
                        /*
                         * Passes a command to the host command-line interpreter.
                         * This enables you to execute a system command such as dir,
                         * ls, or pwd. The terminal I/O is on the host, and is not
                         * visible to the target.
                         *
                         * Entry
                         * On entry, the PARAMETER REGISTER contains a pointer to a
                         * two-field argument block:
                         * - field 1 Points to a string to be passed to the host
                         * command-line interpreter.
                         * - field 2 The length of the string.
                         *
                         * Return
                         * On exit, the RETURN REGISTER contains the return status.
                         */

                        /* Provide SYS_SYSTEM functionality.  Uses the
                         * libc system command, there may be a reason *NOT*
                         * to use this, but as I can't think of one, I
                         * implemented it this way.
                         */
                        retval = semihosting_read_fields(target, 2, fields);
                        if (retval != ERROR_OK)
                                return retval;
                        else {
                                uint64_t addr = semihosting_get_field(target, 0, fields);
                                size_t len = semihosting_get_field(target, 1, fields);
                                if (semihosting->is_fileio) {
                                        semihosting->hit_fileio = true;
                                        fileio_info->identifier = "system";
                                        fileio_info->param_1 = addr;
                                        fileio_info->param_2 = len;
                                } else {
                                        uint8_t *cmd = malloc(len+1);
                                        if (!cmd) {
                                                semihosting->result = -1;
                                                semihosting->sys_errno = ENOMEM;
                                        } else {
                                                retval = target_read_memory(target,
                                                                addr,
                                                                1,
                                                                len,
                                                                cmd);
                                                if (retval != ERROR_OK) {
                                                        free(cmd);
                                                        return retval;
                                                } else {
                                                        cmd[len] = 0;
                                                        semihosting->result = system(
                                                                        (const char *)cmd);
                                                        LOG_DEBUG("system('%s')=%d",
                                                                cmd,
                                                                (int)semihosting->result);
                                                }

                                                free(cmd);
                                        }
                                }
                        }
                        break;

                case SEMIHOSTING_SYS_TIME:      /* 0x11 */
                        /*
                         * Returns the number of seconds since 00:00 January 1, 1970.
                         * This value is real-world time, regardless of any debug agent
                         * configuration.
                         *
                         * Entry
                         * There are no parameters.
                         *
                         * Return
                         * On exit, the RETURN REGISTER contains the number of seconds.
                         */
                        semihosting->result = time(NULL);
                        break;

                case SEMIHOSTING_SYS_WRITE:     /* 0x05 */
                        /*
                         * Writes the contents of a buffer to a specified file at the
                         * current file position. The file position is specified either:
                         * - Explicitly, by a SYS_SEEK.
                         * - Implicitly as one byte beyond the previous SYS_READ or
                         * SYS_WRITE request.
                         *
                         * The file position is at the start of the file when the file
                         * is opened, and is lost when the file is closed.
                         *
                         * Perform the file operation as a single action whenever
                         * possible. For example, do not split a write of 16KB into
                         * four 4KB chunks unless there is no alternative.
                         *
                         * Entry
                         * On entry, the PARAMETER REGISTER contains a pointer to a
                         * three-field data block:
                         * - field 1 Contains a handle for a file previously opened
                         * with SYS_OPEN.
                         * - field 2 Points to the memory containing the data to be written.
                         * - field 3 Contains the number of bytes to be written from
                         * the buffer to the file.
                         *
                         * Return
                         * On exit, the RETURN REGISTER contains:
                         * - 0 if the call is successful.
                         * - The number of bytes that are not written, if there is an error.
                         */
                        retval = semihosting_read_fields(target, 3, fields);
                        if (retval != ERROR_OK)
                                return retval;
                        else {
                                int fd = semihosting_get_field(target, 0, fields);
                                uint64_t addr = semihosting_get_field(target, 1, fields);
                                size_t len = semihosting_get_field(target, 2, fields);
                                if (semihosting->is_fileio) {
                                        semihosting->hit_fileio = true;
                                        fileio_info->identifier = "write";
                                        fileio_info->param_1 = fd;
                                        fileio_info->param_2 = addr;
                                        fileio_info->param_3 = len;
                                } else {
                                        uint8_t *buf = malloc(len);
                                        if (!buf) {
                                                semihosting->result = -1;
                                                semihosting->sys_errno = ENOMEM;
                                        } else {
                                                retval = target_read_buffer(target, addr, len, buf);
                                                if (retval != ERROR_OK) {
                                                        free(buf);
                                                        return retval;
                                                }
                                                semihosting->result = semihosting_write(semihosting, fd, buf, len);
                                                semihosting->sys_errno = errno;
                                                LOG_DEBUG("write(%d, 0x%" PRIx64 ", %zu)=%d",
                                                        fd,
                                                        addr,
                                                        len,
                                                        (int)semihosting->result);
                                                if (semihosting->result >= 0) {
                                                        /* The number of bytes that are NOT written.
                                                         * */
                                                        semihosting->result = len -
                                                                semihosting->result;
                                                }

                                                free(buf);
                                        }
                                }
                        }
                        break;

                case SEMIHOSTING_SYS_WRITEC:    /* 0x03 */
                        /*
                         * Writes a character byte, pointed to by the PARAMETER REGISTER,
                         * to the debug channel. When executed under a semihosting
                         * debugger, the character appears on the host debugger console.
                         *
                         * Entry
                         * On entry, the PARAMETER REGISTER contains a pointer to the
                         * character.
                         *
                         * Return
                         * None. The RETURN REGISTER is corrupted.
                         */
                        if (semihosting->is_fileio) {
                                semihosting->hit_fileio = true;
                                fileio_info->identifier = "write";
                                fileio_info->param_1 = 1;
                                fileio_info->param_2 = semihosting->param;
                                fileio_info->param_3 = 1;
                        } else {
                                uint64_t addr = semihosting->param;
                                unsigned char c;
                                retval = target_read_memory(target, addr, 1, 1, &c);
                                if (retval != ERROR_OK)
                                        return retval;
                                semihosting_putchar(semihosting, semihosting->stdout_fd, c);
                                semihosting->result = 0;
                        }
                        break;

                case SEMIHOSTING_SYS_WRITE0:    /* 0x04 */
                        /*
                         * Writes a null-terminated string to the debug channel.
                         * When executed under a semihosting debugger, the characters
                         * appear on the host debugger console.
                         *
                         * Entry
                         * On entry, the PARAMETER REGISTER contains a pointer to the
                         * first byte of the string.
                         *
                         * Return
                         * None. The RETURN REGISTER is corrupted.
                         */
                        if (semihosting->is_fileio) {
                                size_t count = 0;
                                uint64_t addr = semihosting->param;
                                for (;; addr++) {
                                        unsigned char c;
                                        retval = target_read_memory(target, addr, 1, 1, &c);
                                        if (retval != ERROR_OK)
                                                return retval;
                                        if (c == '\0')
                                                break;
                                        count++;
                                }
                                semihosting->hit_fileio = true;
                                fileio_info->identifier = "write";
                                fileio_info->param_1 = 1;
                                fileio_info->param_2 = semihosting->param;
                                fileio_info->param_3 = count;
                        } else {
                                uint64_t addr = semihosting->param;
                                do {
                                        unsigned char c;
                                        retval = target_read_memory(target, addr++, 1, 1, &c);
                                        if (retval != ERROR_OK)
                                                return retval;
                                        if (!c)
                                                break;
                                        semihosting_putchar(semihosting, semihosting->stdout_fd, c);
                                } while (1);
                                semihosting->result = 0;
                        }
                        break;

                case SEMIHOSTING_USER_CMD_0x100 ... SEMIHOSTING_USER_CMD_0x107:
                        /**
                         * This is a user defined operation (while user cmds 0x100-0x1ff
                         * are possible, only 0x100-0x107 are currently implemented).
                         *
                         * Reads the user operation parameters from target, then fires the
                         * corresponding target event. When the target callbacks returned,
                         * cleans up the command parameter buffer.
                         *
                         * Entry
                         * On entry, the PARAMETER REGISTER contains a pointer to a
                         * two-field data block:
                         * - field 1 Contains a pointer to the bound command parameter
                         * string
                         * - field 2 Contains the command parameter string length
                         *
                         * Return
                         * On exit, the RETURN REGISTER contains the return status.
                         */
                {
                        assert(!semihosting_user_op_params);

                        retval = semihosting_read_fields(target, 2, fields);
                        if (retval != ERROR_OK) {
                                LOG_ERROR("Failed to read fields for user defined command"
                                                " op=0x%x", semihosting->op);
                                return retval;
                        }

                        uint64_t addr = semihosting_get_field(target, 0, fields);

                        size_t len = semihosting_get_field(target, 1, fields);
                        if (len > SEMIHOSTING_MAX_TCL_COMMAND_FIELD_LENGTH) {
                                LOG_ERROR("The maximum length for user defined command "
                                                "parameter is %u, received length is %zu (op=0x%x)",
                                                SEMIHOSTING_MAX_TCL_COMMAND_FIELD_LENGTH,
                                                len,
                                                semihosting->op);
                                return ERROR_FAIL;
                        }

                        semihosting_user_op_params = malloc(len + 1);
                        if (!semihosting_user_op_params)
                                return ERROR_FAIL;
                        semihosting_user_op_params[len] = 0;

                        retval = target_read_buffer(target, addr, len,
                                        (uint8_t *)(semihosting_user_op_params));
                        if (retval != ERROR_OK) {
                                LOG_ERROR("Failed to read from target, semihosting op=0x%x",
                                                semihosting->op);
                                free(semihosting_user_op_params);
                                semihosting_user_op_params = NULL;
                                return retval;
                        }

                        target_handle_event(target, semihosting->op);
                        free(semihosting_user_op_params);
                        semihosting_user_op_params = NULL;

                        semihosting->result = 0;
                        break;
                }


                case SEMIHOSTING_SYS_ELAPSED:   /* 0x30 */
                /*
                 * Returns the number of elapsed target ticks since execution
                 * started.
                 * Use SYS_TICKFREQ to determine the tick frequency.
                 *
                 * Entry (32-bit)
                 * On entry, the PARAMETER REGISTER points to a two-field data
                 * block to be used for returning the number of elapsed ticks:
                 * - field 1 The least significant field and is at the low address.
                 * - field 2 The most significant field and is at the high address.
                 *
                 * Entry (64-bit)
                 * On entry the PARAMETER REGISTER points to a one-field data
                 * block to be used for returning the number of elapsed ticks:
                 * - field 1 The number of elapsed ticks as a 64-bit value.
                 *
                 * Return
                 * On exit:
                 * - On success, the RETURN REGISTER contains 0, the PARAMETER
                 * REGISTER is unchanged, and the data block pointed to by the
                 * PARAMETER REGISTER is filled in with the number of elapsed
                 * ticks.
                 * - On failure, the RETURN REGISTER contains -1, and the
                 * PARAMETER REGISTER contains -1.
                 *
                 * Note: Some semihosting implementations might not support this
                 * semihosting operation, and they always return -1 in the
                 * RETURN REGISTER.
                 */

                case SEMIHOSTING_SYS_TICKFREQ:  /* 0x31 */
                /*
                 * Returns the tick frequency.
                 *
                 * Entry
                 * The PARAMETER REGISTER must contain 0 on entry to this routine.
                 *
                 * Return
                 * On exit, the RETURN REGISTER contains either:
                 * - The number of ticks per second.
                 * - –1 if the target does not know the value of one tick.
                 *
                 * Note: Some semihosting implementations might not support
                 * this semihosting operation, and they always return -1 in the
                 * RETURN REGISTER.
                 */

                case SEMIHOSTING_SYS_TMPNAM:    /* 0x0D */
                /*
                 * Returns a temporary name for a file identified by a system
                 * file identifier.
                 *
                 * Entry
                 * On entry, the PARAMETER REGISTER contains a pointer to a
                 * three-word argument block:
                 * - field 1 A pointer to a buffer.
                 * - field 2 A target identifier for this filename. Its value
                 * must be an integer in the range 0-255.
                 * - field 3 Contains the length of the buffer. The length must
                 * be at least the value of L_tmpnam on the host system.
                 *
                 * Return
                 * On exit, the RETURN REGISTER contains:
                 * - 0 if the call is successful.
                 * - –1 if an error occurs.
                 *
                 * The buffer pointed to by the PARAMETER REGISTER contains
                 * the filename, prefixed with a suitable directory name.
                 * If you use the same target identifier again, the same
                 * filename is returned.
                 *
                 * Note: The returned string must be null-terminated.
                 */

                default:
                        fprintf(stderr, "semihosting: unsupported call %#x\n",
                                (unsigned) semihosting->op);
                        semihosting->result = -1;
                        semihosting->sys_errno = ENOTSUP;
        }

        if (!semihosting->hit_fileio) {
                retval = semihosting->post_result(target);
                if (retval != ERROR_OK) {
                        LOG_ERROR("Failed to post semihosting result");
                        return retval;
                }
        }

        return ERROR_OK;
}

/* -------------------------------------------------------------------------
 * Local functions. */

static int semihosting_common_fileio_info(struct target *target,
        struct gdb_fileio_info *fileio_info)
{
        struct semihosting *semihosting = target->semihosting;
        if (!semihosting)
                return ERROR_FAIL;

        /*
         * To avoid unnecessary duplication, semihosting prepares the
         * fileio_info structure out-of-band when the target halts. See
         * do_semihosting for more detail.
         */
        if (!semihosting->is_fileio || !semihosting->hit_fileio)
                return ERROR_FAIL;

        return ERROR_OK;
}

static int semihosting_common_fileio_end(struct target *target, int result,
        int fileio_errno, bool ctrl_c)
{
        struct gdb_fileio_info *fileio_info = target->fileio_info;
        struct semihosting *semihosting = target->semihosting;
        if (!semihosting)
                return ERROR_FAIL;

        /* clear pending status */
        semihosting->hit_fileio = false;

        semihosting->result = result;
        semihosting->sys_errno = fileio_errno;

        /*
         * Some fileio results do not match up with what the semihosting
         * operation expects; for these operations, we munge the results
         * below:
         */
        switch (semihosting->op) {
                case SEMIHOSTING_SYS_WRITE:     /* 0x05 */
                        if (result < 0)
                                semihosting->result = fileio_info->param_3;
                        else
                                semihosting->result = 0;
                        break;

                case SEMIHOSTING_SYS_READ:      /* 0x06 */
                        if (result == (int)fileio_info->param_3)
                                semihosting->result = 0;
                        if (result <= 0)
                                semihosting->result = fileio_info->param_3;
                        break;

                case SEMIHOSTING_SYS_SEEK:      /* 0x0a */
                        if (result > 0)
                                semihosting->result = 0;
                        break;
        }

        return semihosting->post_result(target);
}

/**
 * Read all fields of a command from target to buffer.
 */
static int semihosting_read_fields(struct target *target, size_t number,
        uint8_t *fields)
{
        struct semihosting *semihosting = target->semihosting;
        /* Use 4-byte multiples to trigger fast memory access. */
        return target_read_memory(target, semihosting->param, 4,
                        number * (semihosting->word_size_bytes / 4), fields);
}

/**
 * Write all fields of a command from buffer to target.
 */
static int semihosting_write_fields(struct target *target, size_t number,
        uint8_t *fields)
{
        struct semihosting *semihosting = target->semihosting;
        /* Use 4-byte multiples to trigger fast memory access. */
        return target_write_memory(target, semihosting->param, 4,
                        number * (semihosting->word_size_bytes / 4), fields);
}

/**
 * Extract a field from the buffer, considering register size and endianness.
 */
static uint64_t semihosting_get_field(struct target *target, size_t index,
        uint8_t *fields)
{
        struct semihosting *semihosting = target->semihosting;
        if (semihosting->word_size_bytes == 8)
                return target_buffer_get_u64(target, fields + (index * 8));
        else
                return target_buffer_get_u32(target, fields + (index * 4));
}

/**
 * Store a field in the buffer, considering register size and endianness.
 */
static void semihosting_set_field(struct target *target, uint64_t value,
        size_t index,
        uint8_t *fields)
{
        struct semihosting *semihosting = target->semihosting;
        if (semihosting->word_size_bytes == 8)
                target_buffer_set_u64(target, fields + (index * 8), value);
        else
                target_buffer_set_u32(target, fields + (index * 4), value);
}

/* -------------------------------------------------------------------------
 * Semihosting redirect over TCP structs and functions */

static int semihosting_service_new_connection_handler(struct connection *connection)
{
        struct semihosting_tcp_service *service = connection->service->priv;
        service->semihosting->tcp_connection = connection;

        return ERROR_OK;
}

static int semihosting_service_input_handler(struct connection *connection)
{
        struct semihosting_tcp_service *service = connection->service->priv;

        if (!connection->input_pending) {
                /* consume received data, not for semihosting IO */
                const int buf_len = 100;
                char buf[buf_len];
                int bytes_read = connection_read(connection, buf, buf_len);

                if (bytes_read == 0) {
                        return ERROR_SERVER_REMOTE_CLOSED;
                } else if (bytes_read == -1) {
                        LOG_ERROR("error during read: %s", strerror(errno));
                        return ERROR_SERVER_REMOTE_CLOSED;
                }
        } else if (service->error != ERROR_OK) {
                return ERROR_SERVER_REMOTE_CLOSED;
        }

        return ERROR_OK;
}

static int semihosting_service_connection_closed_handler(struct connection *connection)
{
        struct semihosting_tcp_service *service = connection->service->priv;
        if (service) {
                free(service->name);
                free(service);
        }

        return ERROR_OK;
}

static void semihosting_tcp_close_cnx(struct semihosting *semihosting)
{
        if (!semihosting->tcp_connection)
                return;

        struct service *service = semihosting->tcp_connection->service;
        remove_service(service->name, service->port);
        semihosting->tcp_connection = NULL;

}

static const struct service_driver semihosting_service_driver = {
        .name = "semihosting",
        .new_connection_during_keep_alive_handler = NULL,
        .new_connection_handler = semihosting_service_new_connection_handler,
        .input_handler = semihosting_service_input_handler,
        .connection_closed_handler = semihosting_service_connection_closed_handler,
        .keep_client_alive_handler = NULL,
};

/* -------------------------------------------------------------------------
 * Common semihosting commands handlers. */

COMMAND_HANDLER(handle_common_semihosting_command)
{
        struct target *target = get_current_target(CMD_CTX);

        if (!target) {
                LOG_ERROR("No target selected");
                return ERROR_FAIL;
        }

        struct semihosting *semihosting = target->semihosting;
        if (!semihosting) {
                command_print(CMD, "semihosting not supported for current target");
                return ERROR_FAIL;
        }

        if (CMD_ARGC > 0) {
                int is_active;

                COMMAND_PARSE_ENABLE(CMD_ARGV[0], is_active);

                if (!target_was_examined(target)) {
                        LOG_ERROR("Target not examined yet");
                        return ERROR_FAIL;
                }

                if (semihosting && semihosting->setup(target, is_active) != ERROR_OK) {
                        LOG_ERROR("Failed to Configure semihosting");
                        return ERROR_FAIL;
                }

                /* FIXME never let that "catch" be dropped! (???) */
                semihosting->is_active = is_active;
        }

        command_print(CMD, "semihosting is %s",
                semihosting->is_active
                ? "enabled" : "disabled");

        return ERROR_OK;
}

COMMAND_HANDLER(handle_common_semihosting_redirect_command)
{
        struct target *target = get_current_target(CMD_CTX);

        if (target == NULL) {
                LOG_ERROR("No target selected");
                return ERROR_FAIL;
        }

        struct semihosting *semihosting = target->semihosting;
        if (!semihosting) {
                command_print(CMD, "semihosting not supported for current target");
                return ERROR_FAIL;
        }

        if (!semihosting->is_active) {
                command_print(CMD, "semihosting not yet enabled for current target");
                return ERROR_FAIL;
        }

        enum semihosting_redirect_config cfg;
        const char *port;

        if (CMD_ARGC < 1)
                return ERROR_COMMAND_SYNTAX_ERROR;

        if (strcmp(CMD_ARGV[0], "disable") == 0) {
                cfg = SEMIHOSTING_REDIRECT_CFG_NONE;
                if (CMD_ARGC > 1)
                        return ERROR_COMMAND_SYNTAX_ERROR;
        } else if (strcmp(CMD_ARGV[0], "tcp") == 0) {
                if (CMD_ARGC < 2 || CMD_ARGC > 3)
                        return ERROR_COMMAND_SYNTAX_ERROR;

                port = CMD_ARGV[1];

                cfg = SEMIHOSTING_REDIRECT_CFG_ALL;
                if (CMD_ARGC == 3) {
                        if (strcmp(CMD_ARGV[2], "debug") == 0)
                                cfg = SEMIHOSTING_REDIRECT_CFG_DEBUG;
                        else if (strcmp(CMD_ARGV[2], "stdio") == 0)
                                cfg = SEMIHOSTING_REDIRECT_CFG_STDIO;
                        else if (strcmp(CMD_ARGV[2], "all") != 0)
                                return ERROR_COMMAND_SYNTAX_ERROR;
                }
        } else {
                return ERROR_COMMAND_SYNTAX_ERROR;
        }

        semihosting_tcp_close_cnx(semihosting);
        semihosting->redirect_cfg = SEMIHOSTING_REDIRECT_CFG_NONE;

        if (cfg != SEMIHOSTING_REDIRECT_CFG_NONE) {
                struct semihosting_tcp_service *service =
                                calloc(1, sizeof(struct semihosting_tcp_service));
                if (!service) {
                        LOG_ERROR("Failed to allocate semihosting TCP service.");
                        return ERROR_FAIL;
                }

                service->semihosting = semihosting;

                service->name = alloc_printf("%s semihosting service", target_name(target));
                if (!service->name) {
                        LOG_ERROR("Out of memory");
                        free(service);
                        return ERROR_FAIL;
                }

                int ret = add_service(&semihosting_service_driver,
                                port, 1, service);

                if (ret != ERROR_OK) {
                        LOG_ERROR("failed to initialize %s", service->name);
                        free(service->name);
                        free(service);
                        return ERROR_FAIL;
                }
        }

        semihosting->redirect_cfg = cfg;

        return ERROR_OK;
}

COMMAND_HANDLER(handle_common_semihosting_fileio_command)
{
        struct target *target = get_current_target(CMD_CTX);

        if (!target) {
                LOG_ERROR("No target selected");
                return ERROR_FAIL;
        }

        struct semihosting *semihosting = target->semihosting;
        if (!semihosting) {
                command_print(CMD, "semihosting not supported for current target");
                return ERROR_FAIL;
        }

        if (!semihosting->is_active) {
                command_print(CMD, "semihosting not yet enabled for current target");
                return ERROR_FAIL;
        }

        if (CMD_ARGC > 0)
                COMMAND_PARSE_ENABLE(CMD_ARGV[0], semihosting->is_fileio);

        command_print(CMD, "semihosting fileio is %s",
                semihosting->is_fileio
                ? "enabled" : "disabled");

        return ERROR_OK;
}

COMMAND_HANDLER(handle_common_semihosting_cmdline)
{
        struct target *target = get_current_target(CMD_CTX);
        unsigned int i;

        if (!target) {
                LOG_ERROR("No target selected");
                return ERROR_FAIL;
        }

        struct semihosting *semihosting = target->semihosting;
        if (!semihosting) {
                command_print(CMD, "semihosting not supported for current target");
                return ERROR_FAIL;
        }

        free(semihosting->cmdline);
        semihosting->cmdline = CMD_ARGC > 0 ? strdup(CMD_ARGV[0]) : NULL;

        for (i = 1; i < CMD_ARGC; i++) {
                char *cmdline = alloc_printf("%s %s", semihosting->cmdline, CMD_ARGV[i]);
                if (!cmdline)
                        break;
                free(semihosting->cmdline);
                semihosting->cmdline = cmdline;
        }

        command_print(CMD, "semihosting command line is [%s]",
                semihosting->cmdline);

        return ERROR_OK;
}

COMMAND_HANDLER(handle_common_semihosting_resumable_exit_command)
{
        struct target *target = get_current_target(CMD_CTX);

        if (!target) {
                LOG_ERROR("No target selected");
                return ERROR_FAIL;
        }

        struct semihosting *semihosting = target->semihosting;
        if (!semihosting) {
                command_print(CMD, "semihosting not supported for current target");
                return ERROR_FAIL;
        }

        if (!semihosting->is_active) {
                command_print(CMD, "semihosting not yet enabled for current target");
                return ERROR_FAIL;
        }

        if (CMD_ARGC > 0)
                COMMAND_PARSE_ENABLE(CMD_ARGV[0], semihosting->has_resumable_exit);

        command_print(CMD, "semihosting resumable exit is %s",
                semihosting->has_resumable_exit
                ? "enabled" : "disabled");

        return ERROR_OK;
}

COMMAND_HANDLER(handle_common_semihosting_read_user_param_command)
{
        struct target *target = get_current_target(CMD_CTX);
        struct semihosting *semihosting = target->semihosting;

        if (CMD_ARGC)
                return ERROR_COMMAND_SYNTAX_ERROR;

        if (!semihosting->is_active) {
                LOG_ERROR("semihosting not yet enabled for current target");
                return ERROR_FAIL;
        }

        if (!semihosting_user_op_params) {
                LOG_ERROR("This command is usable only from a registered user "
                                "semihosting event callback.");
                return ERROR_FAIL;
        }

        command_print_sameline(CMD, "%s", semihosting_user_op_params);

        return ERROR_OK;
}

COMMAND_HANDLER(handle_common_semihosting_basedir_command)
{
        struct target *target = get_current_target(CMD_CTX);

        if (CMD_ARGC > 1)
                return ERROR_COMMAND_SYNTAX_ERROR;

        if (!target) {
                LOG_ERROR("No target selected");
                return ERROR_FAIL;
        }

        struct semihosting *semihosting = target->semihosting;
        if (!semihosting) {
                command_print(CMD, "semihosting not supported for current target");
                return ERROR_FAIL;
        }

        if (!semihosting->is_active) {
                command_print(CMD, "semihosting not yet enabled for current target");
                return ERROR_FAIL;
        }

        if (CMD_ARGC > 0) {
                free(semihosting->basedir);
                semihosting->basedir = strdup(CMD_ARGV[0]);
                if (!semihosting->basedir) {
                        command_print(CMD, "semihosting failed to allocate memory for basedir!");
                        return ERROR_FAIL;
                }
        }

        command_print(CMD, "semihosting base dir: %s",
                semihosting->basedir ? semihosting->basedir : "");

        return ERROR_OK;
}

const struct command_registration semihosting_common_handlers[] = {
        {
                .name = "semihosting",
                .handler = handle_common_semihosting_command,
                .mode = COMMAND_EXEC,
                .usage = "['enable'|'disable']",
                .help = "activate support for semihosting operations",
        },
        {
                .name = "semihosting_redirect",
                .handler = handle_common_semihosting_redirect_command,
                .mode = COMMAND_EXEC,
                .usage = "(disable | tcp <port> ['debug'|'stdio'|'all'])",
                .help = "redirect semihosting IO",
        },
        {
                .name = "semihosting_cmdline",
                .handler = handle_common_semihosting_cmdline,
                .mode = COMMAND_EXEC,
                .usage = "arguments",
                .help = "command line arguments to be passed to program",
        },
        {
                .name = "semihosting_fileio",
                .handler = handle_common_semihosting_fileio_command,
                .mode = COMMAND_EXEC,
                .usage = "['enable'|'disable']",
                .help = "activate support for semihosting fileio operations",
        },
        {
                .name = "semihosting_resexit",
                .handler = handle_common_semihosting_resumable_exit_command,
                .mode = COMMAND_EXEC,
                .usage = "['enable'|'disable']",
                .help = "activate support for semihosting resumable exit",
        },
        {
                .name = "semihosting_read_user_param",
                .handler = handle_common_semihosting_read_user_param_command,
                .mode = COMMAND_EXEC,
                .usage = "",
                .help = "read parameters in semihosting-user-cmd-0x10X callbacks",
        },
        {
                .name = "semihosting_basedir",
                .handler = handle_common_semihosting_basedir_command,
                .mode = COMMAND_EXEC,
                .usage = "[dir]",
                .help = "set the base directory for semihosting I/O operations",
        },
        COMMAND_REGISTRATION_DONE
};