几种backtrace方法

backtrace就是回溯程序的函数栈，我们在代码调试中经常会遇到，现总结下笔者所知道的以下四种backtrace方式：

1、直接调用libc函数 int  backtrace(void**, int)

2、通过gcc内置函数__builtin_return_address获取函数返回地址，从而得到栈信息，只能是默认优化等级，即-O0，否则无法使用

3、直接内嵌汇编指令，读取寄存器数据，获取函数返回地址， 和2一样，只能-O0

4、使用libunwind.so接口函数int  unw_backtrace (void**, int)

对比上述4种方式的性能， 1）的性能最差，和2）、3）、4）差一个数量级； 2）和3）性能最好， 性能是4）的3倍多

具体测试代码如下：

#include <execinfo.h>
#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <dlfcn.h>
#include <thread>
#include <dlfcn.h>

/*  gcc内置函数 */
/***********************************************/
#define GCCBT(i) \
    if(i >= size) return i;\
    frameNow = __builtin_frame_address(i);\
    if((unsigned long)frameNow <= (unsigned long)frameLast ||\
    ((unsigned long)frameLast != 0 && (unsigned long)frameNow > (unsigned long)frameLast + (1ULL<<24)))\
        return i;\
    frameLast = frameNow;\
    stack[i] = __builtin_extract_return_addr(__builtin_return_address(i));\

static int gccBacktrace(void** stack, int size)
{
    void* frameNow = 0; 
    void* frameLast = 0;
    GCCBT(0); GCCBT(1); GCCBT(2); GCCBT(3); GCCBT(4); GCCBT(5); GCCBT(6); GCCBT(7);
    GCCBT(8); GCCBT(9); GCCBT(10); GCCBT(11); GCCBT(12); GCCBT(13); GCCBT(14); GCCBT(15);
    GCCBT(16); GCCBT(17); GCCBT(18); GCCBT(19); GCCBT(20); GCCBT(21); GCCBT(22); GCCBT(23);
    GCCBT(24); GCCBT(25); GCCBT(26); GCCBT(27); GCCBT(28); GCCBT(29); GCCBT(30); GCCBT(31);
    return 32;
}

/*  内置汇编获取寄存器返回值 */
/***********************************************/
static int asmBacktrace(void** stack, int size)
{
#ifndef __x86_64__
    return 0;
#else
    int frame = 0;
    void ** ebp;
    unsigned long long func_frame_distance = 0;
    __asm__ __volatile__("mov %%rbp, %0;\n\t" : "=m"(ebp) ::"memory");
    while (ebp && frame < size
        && (unsigned long long)(*ebp) < (unsigned long long)(ebp) + (1ULL << 24)//16M
        && (unsigned long long)(*ebp) > (unsigned long long)(ebp))
    {
        stack[frame++] = *(ebp + 1);
        ebp = (void**)(*ebp);
    }
    return frame;
#endif
}

static int flag = 1;
static int(*pfnBt)(void**, int);
void func5()
{
    void *btbuf[16];
    int btnum = pfnBt(btbuf, 16);
    if (flag == 1)
    {
        flag = 2;
        char **strings = backtrace_symbols(btbuf, btnum);
        for (int i = 0; i < btnum; ++i)
        {
            printf("%p %s\n", btbuf[i], strings[i]);
        }
        free(strings);
    }
}
void func4()
{
    func5();
}

void func3()
{
    func4();
}
void func2()
{
    func3();
}
void func1(int num)
{
    for (int i = 0; i < num; ++i)
    {
        func2();
    }
}

int main(int argc, char** argv)
{
    if (argc != 3)
    {
        printf("param1: int -- each thread loop number\n");
        printf("param2: string --bt method libc/gcc/asm/unw\n");
        return -1;
    }
    int loopNum = atoi(argv[1]);
    std::string method = argv[2];
    if (method == "libc")
    {
        printf("test libc\n");
        pfnBt = backtrace;
    }
    else if (method == "gcc")
    {
        printf("test gcc\n");
        pfnBt = gccBacktrace;
    }
    else if (method == "asm")
    {
        printf("test asm\n");
        pfnBt = asmBacktrace;
    }
    else if (method == "uwn")
    {
        printf("test uwn\n");
        void* handle = dlopen("./libunwind.so",RTLD_LAZY|RTLD_LOCAL);
        if (handle == NULL)
        {
            printf("dlopen failed, %s\n", dlerror());
            return -1;
        }
        pfnBt = (int(*)(void**, int))dlsym(handle, "unw_backtrace");
        if (pfnBt == NULL)
        {
            printf("dlsym failed, %s\n", dlerror());
            return -1;
        }
    }
    else
    {
        printf("please input right method lic/gcc/asm/uwn\n");
        return -1;
    }
    std::thread thd[20];
    for (int i = 0; i < 20; ++i)
    {
        thd[i] = std::thread(func1, loopNum);
    }
    for (int i = 0; i < 20; ++i)
    {
        thd[i].join();
    }
    return 0;
}

编译命令：

　　g++ bt.cpp -o bt -lpthread -ldl -std=c++11 -g

对比测试效果截图如下：