riscv_semihosting.c

Go to the documentation of this file.

// SPDX-License-Identifier: GPL-2.0-or-later
 
/***************************************************************************
 *   Copyright (C) 2018 by Liviu Ionescu                                   *
 *   ilg@livius.net                                                        *
 *                                                                         *
 *   Copyright (C) 2009 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 <helper/log.h>
 
#include "target/target.h"
#include "riscv.h"
 
static int riscv_semihosting_setup(struct target *target, int enable);
static int riscv_semihosting_post_result(struct target *target);
 
void riscv_semihosting_init(struct target *target)
{
    semihosting_common_init(target, riscv_semihosting_setup,
        riscv_semihosting_post_result);
}
 
enum semihosting_result riscv_semihosting(struct target *target, int *retval)
{
    struct semihosting *semihosting = target->semihosting;
    if (!semihosting) {
        LOG_DEBUG("   -> NONE (!semihosting)");
        return SEMIHOSTING_NONE;
    }
 
    if (!semihosting->is_active) {
        LOG_DEBUG("   -> NONE (!semihosting->is_active)");
        return SEMIHOSTING_NONE;
    }
 
    riscv_reg_t pc;
    int result = riscv_get_register(target, &pc, GDB_REGNO_PC);
    if (result != ERROR_OK)
        return SEMIHOSTING_ERROR;
 
    uint8_t tmp_buf[12];
 
    /* Read three uncompressed instructions: The previous, the current one (pointed to by PC) and the next one */
    for (int i = 0; i < 3; i++) {
        /* Instruction memories may not support arbitrary read size. Use any size that will work. */
        *retval = riscv_read_by_any_size(target, (pc - 4) + 4 * i, 4, tmp_buf + 4 * i);
        if (*retval != ERROR_OK)
            return SEMIHOSTING_ERROR;
    }
 
    /*
     * The instructions that trigger a semihosting call,
     * always uncompressed, should look like:
     *
     * 01f01013              slli    zero,zero,0x1f
     * 00100073              ebreak
     * 40705013              srai    zero,zero,0x7
     */
    uint32_t pre = target_buffer_get_u32(target, tmp_buf);
    uint32_t ebreak = target_buffer_get_u32(target, tmp_buf + 4);
    uint32_t post = target_buffer_get_u32(target, tmp_buf + 8);
    LOG_DEBUG("check %08x %08x %08x from 0x%" PRIx64 "-4", pre, ebreak, post, pc);
 
    if (pre != 0x01f01013 || ebreak != 0x00100073 || post != 0x40705013) {
        /* Not the magic sequence defining semihosting. */
        LOG_DEBUG("   -> NONE (no magic)");
        return SEMIHOSTING_NONE;
    }
 
    /*
     * Perform semihosting call if we are not waiting on a fileio
     * operation to complete.
     */
    if (!semihosting->hit_fileio) {
        /* RISC-V uses A0 and A1 to pass function arguments */
        riscv_reg_t r0;
        riscv_reg_t r1;
 
        result = riscv_get_register(target, &r0, GDB_REGNO_A0);
        if (result != ERROR_OK) {
            LOG_DEBUG("   -> ERROR (couldn't read a0)");
            return SEMIHOSTING_ERROR;
        }
 
        result = riscv_get_register(target, &r1, GDB_REGNO_A1);
        if (result != ERROR_OK) {
            LOG_DEBUG("   -> ERROR (couldn't read a1)");
            return SEMIHOSTING_ERROR;
        }
 
        semihosting->op = r0;
        semihosting->param = r1;
        semihosting->word_size_bytes = riscv_xlen(target) / 8;
 
        /* Check for ARM operation numbers. */
        if ((semihosting->op >= 0 && semihosting->op <= 0x31) ||
            (semihosting->op >= 0x100 && semihosting->op <= 0x107)) {
 
            *retval = semihosting_common(target);
            if (*retval != ERROR_OK) {
                LOG_ERROR("Failed semihosting operation (0x%02X)", semihosting->op);
                return SEMIHOSTING_ERROR;
            }
        } else {
            /* Unknown operation number, not a semihosting call. */
            LOG_DEBUG("   -> NONE (unknown operation number)");
            return SEMIHOSTING_NONE;
        }
    }
 
    /* Resume right after the EBREAK 4 bytes instruction. */
    *retval = riscv_set_register(target, GDB_REGNO_PC, pc + 4);
    if (*retval != ERROR_OK)
        return SEMIHOSTING_ERROR;
 
    /*
     * Resume target if we are not waiting on a fileio
     * operation to complete.
     */
    if (semihosting->is_resumable && !semihosting->hit_fileio) {
        LOG_DEBUG("   -> HANDLED");
        return SEMIHOSTING_HANDLED;
    }
 
    LOG_DEBUG("   -> WAITING");
    return SEMIHOSTING_WAITING;
}
 
/* -------------------------------------------------------------------------
 * Local functions. */
 
static int riscv_semihosting_setup(struct target *target, int enable)
{
    LOG_DEBUG("[%s] enable=%d", target_name(target), enable);
 
    struct semihosting *semihosting = target->semihosting;
    if (semihosting)
        semihosting->setup_time = clock();
 
    return ERROR_OK;
}
 
static int riscv_semihosting_post_result(struct target *target)
{
    struct semihosting *semihosting = target->semihosting;
    if (!semihosting) {
        /* If not enabled, silently ignored. */
        return 0;
    }
 
    LOG_DEBUG("0x%" PRIx64, semihosting->result);
    riscv_set_register(target, GDB_REGNO_A0, semihosting->result);
    return 0;
}