semihosting_common.c

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// SPDX-License-Identifier: GPL-2.0-or-later
 
/***************************************************************************
 *   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>                               *
 ***************************************************************************/
 
#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 <server/gdb_server.h>
#include <sys/stat.h>
 
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 void semihosting_set_field(struct target *target, uint64_t value, size_t index, uint8_t *fields);
static int semihosting_write_fields(struct target *target, size_t number, uint8_t *fields);
 
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;
    semihosting->user_command_extension = NULL;
 
    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 */
    int result = write(fd, buf, size);
    if (result == -1)
        semihosting->sys_errno = errno;
    return result;
}
 
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);
    if (result == -1)
        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();
}
 
static char *semihosting_user_op_params;
 
static const char *semihosting_opcode_to_str(const uint64_t opcode)
{
    switch (opcode) {
    case SEMIHOSTING_SYS_CLOSE:
        return "CLOSE";
    case SEMIHOSTING_SYS_CLOCK:
        return "CLOCK";
    case SEMIHOSTING_SYS_ELAPSED:
        return "ELAPSED";
    case SEMIHOSTING_SYS_ERRNO:
        return "ERRNO";
    case SEMIHOSTING_SYS_EXIT:
        return "EXIT";
    case SEMIHOSTING_SYS_EXIT_EXTENDED:
        return "EXIT_EXTENDED";
    case SEMIHOSTING_SYS_FLEN:
        return "FLEN";
    case SEMIHOSTING_SYS_GET_CMDLINE:
        return "GET_CMDLINE";
    case SEMIHOSTING_SYS_HEAPINFO:
        return "HEAPINFO";
    case SEMIHOSTING_SYS_ISERROR:
        return "ISERROR";
    case SEMIHOSTING_SYS_ISTTY:
        return "ISTTY";
    case SEMIHOSTING_SYS_OPEN:
        return "OPEN";
    case SEMIHOSTING_SYS_READ:
        return "READ";
    case SEMIHOSTING_SYS_READC:
        return "READC";
    case SEMIHOSTING_SYS_REMOVE:
        return "REMOVE";
    case SEMIHOSTING_SYS_RENAME:
        return "RENAME";
    case SEMIHOSTING_SYS_SEEK:
        return "SEEK";
    case SEMIHOSTING_SYS_SYSTEM:
        return "SYSTEM";
    case SEMIHOSTING_SYS_TICKFREQ:
        return "TICKFREQ";
    case SEMIHOSTING_SYS_TIME:
        return "TIME";
    case SEMIHOSTING_SYS_TMPNAM:
        return "TMPNAM";
    case SEMIHOSTING_SYS_WRITE:
        return "WRITE";
    case SEMIHOSTING_SYS_WRITEC:
        return "WRITEC";
    case SEMIHOSTING_SYS_WRITE0:
        return "WRITE0";
    case SEMIHOSTING_USER_CMD_0X100 ... SEMIHOSTING_USER_CMD_0X1FF:
        return "USER_CMD";
    case SEMIHOSTING_ARM_RESERVED_START ... SEMIHOSTING_ARM_RESERVED_END:
        return "ARM_RESERVED_CMD";
    default:
        return "<unknown>";
    }
}
 
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 (%s), param=0x%" PRIx64, semihosting->op,
              semihosting_opcode_to_str(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;
 
        {
            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 */
                semihosting->result = 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);
                if (semihosting->result == -1)
                    semihosting->sys_errno = errno;
                LOG_DEBUG("close(%d)=%" PRId64, fd, 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;
 
            int type = semihosting_get_field(target, 0, fields);
            int code = semihosting_get_field(target, 1, fields);
 
            if (type == ADP_STOPPED_APPLICATION_EXIT) {
                if (!gdb_get_actual_connections())
                    exit(code);
 
                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_get_actual_connections())
                    exit(0);
 
                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_get_actual_connections())
                    exit(1);
 
                fprintf(stderr,
                    "semihosting: *** application exited with error ***\n");
            } else {
                if (!gdb_get_actual_connections())
                    exit(1);
 
                fprintf(stderr,
                    "semihosting: application exception %#x\n",
                    (unsigned int)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;
 
        {
            int type = semihosting_get_field(target, 0, fields);
            int code = semihosting_get_field(target, 1, fields);
 
            if (type == ADP_STOPPED_APPLICATION_EXIT) {
                if (!gdb_get_actual_connections())
                    exit(code);
 
                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;
 
        {
            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)=%" PRId64, fd, semihosting->result);
                break;
            }
            LOG_DEBUG("fstat(%d)=%" PRId64, fd, 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;
 
        {
            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], %" PRId64, arg, 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;
 
        {
            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);
            // isatty() on Windows may return any non-zero value if fd is a terminal
            semihosting->result = isatty(fd) ? 1 : 0;
            if (semihosting->result == 0)
                semihosting->sys_errno = errno;
            LOG_DEBUG("isatty(%d)=%" PRId64, fd, 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;
 
        {
            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;
                            semihosting->sys_errno = EINVAL;
                        }
                    } 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 */
                        int fd;
                        if (mode < 4) {
                            fd = dup(STDIN_FILENO);
                            semihosting->stdin_fd = fd;
                            LOG_DEBUG("dup(STDIN)=%d", fd);
                        } else if (mode < 8) {
                            fd = dup(STDOUT_FILENO);
                            semihosting->stdout_fd = fd;
                            LOG_DEBUG("dup(STDOUT)=%d", fd);
                        } else {
                            fd = dup(STDERR_FILENO);
                            semihosting->stderr_fd = fd;
                            LOG_DEBUG("dup(STDERR)=%d", fd);
                        }
                        semihosting->result = fd;
                        if (fd == -1)
                            semihosting->sys_errno = errno;
                    } 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);
                        if (semihosting->result == -1)
                            semihosting->sys_errno = errno;
                        LOG_DEBUG("open('%s')=%" PRId64, fn, 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;
 
        {
            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)=%" PRId64,
                        fd,
                        addr,
                        len,
                        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()=%" PRId64, 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;
 
        {
            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);
                    if (semihosting->result == -1)
                        semihosting->sys_errno = errno;
                    LOG_DEBUG("remove('%s')=%" PRId64, fn, 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;
 
        {
            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);
                    // rename() on Windows returns nonzero on error
                    if (semihosting->result != 0)
                        semihosting->sys_errno = errno;
                    LOG_DEBUG("rename('%s', '%s')=%" PRId64 " %d", fn1, fn2, semihosting->result, errno);
                    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;
 
        {
            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);
                if (semihosting->result == -1)
                    semihosting->sys_errno = errno;
                LOG_DEBUG("lseek(%d, %d)=%" PRId64, fd, (int)pos, 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;
 
        {
            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;
                    }
                    cmd[len] = 0;
                    semihosting->result = system((const char *)cmd);
                    LOG_DEBUG("system('%s')=%" PRId64, cmd, 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;
 
        {
            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);
                    LOG_DEBUG("write(%d, 0x%" PRIx64 ", %zu)=%" PRId64,
                        fd,
                        addr,
                        len,
                        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:
        if (semihosting->user_command_extension) {
            retval = semihosting->user_command_extension(target);
            if (retval != ERROR_NOT_IMPLEMENTED)
                break;
            /* If custom user command not handled, we are looking for the TCL handler */
        }
 
        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 (%s)",
                    semihosting->op,
                    semihosting_opcode_to_str(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 int)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;
 
    /*
     * 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 */
    case SEMIHOSTING_SYS_READ:  /* 0x06 */
        if (result < 0)
            semihosting->result = fileio_info->param_3;  /* Zero bytes read/written. */
        else
            semihosting->result = (int64_t)fileio_info->param_3 - result;
        break;
 
    case SEMIHOSTING_SYS_SEEK:  /* 0x0a */
        if (result > 0)
            semihosting->result = 0;
        break;
    }
 
    bool fileio_failed = false;
    if (semihosting->op == SEMIHOSTING_SYS_ISTTY)
        fileio_failed = (semihosting->result == 0);
    else if (semihosting->op == SEMIHOSTING_SYS_RENAME)
        fileio_failed = (semihosting->result != 0);
    else
        fileio_failed = (semihosting->result == -1);
 
    if (fileio_failed)
        semihosting->sys_errno = fileio_errno;
 
    return semihosting->post_result(target);
}
 
/* -------------------------------------------------------------------------
 * Utility functions. */
 
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);
}
 
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);
}
 
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));
}
 
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);
 
    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) {
        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
};