debugbreak.h

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/* Copyright (c) 2013, Scott Tsai
 *
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#ifndef DEBUG_BREAK_H
#define DEBUG_BREAK_H

#if defined(_MSC_VER) || defined(__MINGW32__)

#define debug_break __debugbreak

#else

#include <signal.h>
#include <unistd.h>
#include <sys/syscall.h>

#ifdef __cplusplus
extern "C" {
#endif

enum {
        /* gcc optimizers consider code after __builtin_trap() dead.
         * Making __builtin_trap() unsuitable for breaking into the debugger */
        DEBUG_BREAK_PREFER_BUILTIN_TRAP_TO_SIGTRAP = 0,
};

#if defined(__i386__) || defined(__x86_64__)
enum { HAVE_TRAP_INSTRUCTION = 1, };
__attribute__((gnu_inline, always_inline))
static void __inline__ trap_instruction(void)
{
        __asm__ volatile("int $0x03");
}
#elif defined(__thumb__)
enum { HAVE_TRAP_INSTRUCTION = 1, };
/* FIXME: handle __THUMB_INTERWORK__ */
__attribute__((gnu_inline, always_inline))
static void __inline__ trap_instruction(void)
{
        /* See 'arm-linux-tdep.c' in GDB source.
         * Both instruction sequences below works. */
#if 1
        /* 'eabi_linux_thumb_le_breakpoint' */
        __asm__ volatile(".inst 0xde01");
#else
        /* 'eabi_linux_thumb2_le_breakpoint' */
        __asm__ volatile(".inst.w 0xf7f0a000");
#endif

        /* Known problem:
         * After a breakpoint hit, can't stepi, step, or continue in GDB.
         * 'step' stuck on the same instruction.
         *
         * Workaround: a new GDB command,
         * 'debugbreak-step' is defined in debugbreak-gdb.py
         * that does:
         * (gdb) set $instruction_len = 2
         * (gdb) tbreak *($pc + $instruction_len)
         * (gdb) jump   *($pc + $instruction_len)
         */
}
#elif defined(__arm__) && !defined(__thumb__)
enum { HAVE_TRAP_INSTRUCTION = 1, };
__attribute__((gnu_inline, always_inline))
static void __inline__ trap_instruction(void)
{
        /* See 'arm-linux-tdep.c' in GDB source,
         * 'eabi_linux_arm_le_breakpoint' */
        __asm__ volatile(".inst 0xe7f001f0");
        /* Has same known problem and workaround
         * as Thumb mode */
}
#else
enum { HAVE_TRAP_INSTRUCTION = 0, };
#endif

__attribute__((gnu_inline, always_inline))
static void __inline__ debug_break(void)
{
#ifdef FASC_BUILD
    __builtin_trap();
#else
        if (HAVE_TRAP_INSTRUCTION) {
#if defined(ETH_EMSCRIPTEN)
                asm("debugger");
#else
                trap_instruction();
#endif
        } else if (DEBUG_BREAK_PREFER_BUILTIN_TRAP_TO_SIGTRAP) {
                 /* raises SIGILL on Linux x86{,-64}, to continue in gdb:
                  * (gdb) handle SIGILL stop nopass
                  * */
                __builtin_trap();
        } else {
                raise(SIGTRAP);
        }
#endif
}

#ifdef __cplusplus
}
#endif

#endif

#endif