// Copyright 2016 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BACKTRACE_REQUEST_BACKTRACE_REQUEST_H_
#define BACKTRACE_REQUEST_BACKTRACE_REQUEST_H_

#include <stdint.h>

// Special value we put in the first register to let the exception handler know
// that we are just requesting a backtrace and we should resume the thread.
#define BACKTRACE_REQUEST_MAGIC ((uint64_t)0xee726573756d65ee)

// Prints a backtrace, resuming the thread without killing the process.
static inline void backtrace_request(void) {
    // Two instructions: one that sets a software breakpoint ("int3" on x64,
    // "brk" on arm64) and one that writes the "magic" value in the first
    // register ("a" on x64, "x0" on arm64).
    //
    // We set a software breakpoint to trigger the exception handling in
    // crashsvc, which will print the debug info, including the backtrace.
    //
    // We write the "magic" value in the first register so that the exception
    // handler can check for it and resume the thread if present.
#ifdef __x86_64__
    __asm__("int3"
            :
            : "a"(BACKTRACE_REQUEST_MAGIC));
#endif
#ifdef __aarch64__
    // This is what gdb uses.
    __asm__("mov x0, %0\n"
            "\tbrk 0"
            :
            : "r"(BACKTRACE_REQUEST_MAGIC)
            : "x0");
#endif
}

#endif // BACKTRACE_REQUEST_BACKTRACE_REQUEST_H_