善用backtrace解决大问题

一．用途：
主要用于程序异常退出时寻找错误原因
二．功能：
回溯堆栈，简单的说就是可以列出当前函数调用关系
三．原理：
1．通过对当前堆栈的分析，找到其上层函数在栈中的帧地址，再分析上层函数的堆栈，再找再上层的帧地址……一直找到最顶层为止，帧地址指的是一块：在栈上存放局部变量，上层返回地址，及寄存器值的空间。
2．由于不同处理器堆栈方式不同，此功能的具体实现是编译器的内建函数__buildin_frame_address及__buildin_return_address中，它涉及工具glibc和gcc, 如果编译器不支持此函数，也可自己实现此函数，举例中有arm上的实现
四．方法：
在程序中加入backtrace及相关函数调用
五．举例：
1．一般backtrace的实现
i. 程序
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <execinfo.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include <unistd.h>
#define PRINT_DEBUG
static void print_reason(int sig, siginfo_t * info, void *secret)
{
void *array[10];
size_t size;
#ifdef PRINT_DEBUG
char **strings;
size_t i;
size = backtrace(array, 10);
strings = backtrace_symbols(array, size);
printf("Obtained %zd stack frames.\n", size);
for (i = 0; i < size; i++)
printf("%s\n", strings[i]);
free(strings);
#else
int fd = open("err.log", O_CREAT | O_WRONLY);
size = backtrace(array, 10);
backtrace_symbols_fd(array, size, fd);
close(fd);
#endif
exit(0);
}
void die()
{
char *test1;
char *test2;
char *test3;
char *test4 = NULL;
strcpy(test4, "ab");
}
void test1()
{
die();
}
int main(int argc, char **argv)
{
struct sigaction myAction;
myAction.sa_sigaction = print_reason;
sigemptyset(&myAction.sa_mask);
myAction.sa_flags = SA_RESTART | SA_SIGINFO;
sigaction(SIGSEGV, &myAction, NULL);
sigaction(SIGUSR1, &myAction, NULL);
sigaction(SIGFPE, &myAction, NULL);
sigaction(SIGILL, &myAction, NULL);
sigaction(SIGBUS, &myAction, NULL);
sigaction(SIGABRT, &myAction, NULL);
sigaction(SIGSYS, &myAction, NULL);
test1();
}
ii. 编译参数
gcc main.c -o test -g -rdynamic
2．根据不同的处理器自已实现backtrace
i. arm的backtrace函数实现
static int backtrace_xy(void **BUFFER, int SIZE)
{
volatile int n = 0;
volatile int *p;
volatile int *q;
volatile int ebp1;
volatile int eip1;
volatile int i = 0;
p = &n;
ebp1 = p[4];
eip1 = p[6];
fprintf(stderr, "======================= backtrace_xy addr: 0x%0x, param1: 0x%0x, param2: 0x%0x\n",
backtrace_xy, &BUFFER, &SIZE);
fprintf(stderr, "n addr is 0x%0x\n", &n);
fprintf(stderr, "p addr is 0x%0x\n", &p);
for (i = 0; i < SIZE; i++)
{
fprintf(stderr, "ebp1 is 0x%0x, eip1 is 0x%0x\n", ebp1, eip1);
BUFFER[i] = (void *)eip1;
p = (int*)ebp1;
q = p - 5;
eip1 = q[5];
ebp1 = q[2];
if (ebp1 == 0 || eip1 == 0)
break;
}
fprintf(stderr, "total level: %d\n", i);
return i;
}
六．举例2：
/*main.c*/
#include "sigsegv.h"
#include <string.h>
int die() {
char *err = NULL;
strcpy(err, "gonner");
return 0;
}
int main() {
return die();
}
/*sigsegv.c*/
#define _GNU_SOURCE
#include <memory.h>
#include <stdlib.h>
#include <stdio.h>
#include <signal.h>
#include <ucontext.h>
#include <dlfcn.h>
#include <execinfo.h>
#define NO_CPP_DEMANGLE
#ifndef NO_CPP_DEMANGLE
#include <cxxabi.h>
#endif
#if defined(REG_RIP)
# define SIGSEGV_STACK_IA64
# define REGFORMAT "%016lx"
#elif defined(REG_EIP)
# define SIGSEGV_STACK_X86
# define REGFORMAT "%08x"
#else
# define SIGSEGV_STACK_GENERIC
# define REGFORMAT "%x"
#endif
static void signal_segv(int signum, siginfo_t* info, void*ptr) {
    static const char *si_codes[3] = {"", "SEGV_MAPERR", "SEGV_ACCERR"};
    size_t i;
    ucontext_t *ucontext = (ucontext_t*)ptr;
#if defined(SIGSEGV_STACK_X86) || defined(SIGSEGV_STACK_IA64)
    int f = 0;
    Dl_info dlinfo;
    void **bp = 0;
    void *ip = 0;
#else
    void *bt[20];
    char **strings;
    size_t sz;
#endif
    fprintf(stderr, "Segmentation Fault!\n");
    fprintf(stderr, "info->si_signo = %d\n", signum);
    fprintf(stderr, "info->si_errno = %d\n", info->si_errno);
//    fprintf(stderr, "info->si_code = %d (%s)\n", info->si_code, info->si_codes[si_code]);
    fprintf(stderr, "info->si_addr = %p\n", info->si_addr);
    for(i = 0; i < NGREG; i++)
        fprintf(stderr, "reg[%02d]       = 0x" REGFORMAT "\n", i, ucontext->uc_mcontext.gregs[i]);
#if defined(SIGSEGV_STACK_X86) || defined(SIGSEGV_STACK_IA64)
# if defined(SIGSEGV_STACK_IA64)
    ip = (void*)ucontext->uc_mcontext.gregs[REG_RIP];
    bp = (void**)ucontext->uc_mcontext.gregs[REG_RBP];
# elif defined(SIGSEGV_STACK_X86)
    ip = (void*)ucontext->uc_mcontext.gregs[REG_EIP];
    bp = (void**)ucontext->uc_mcontext.gregs[REG_EBP];
# endif
    fprintf(stderr, "Stack trace:\n");
    while(bp != & ip) {
        if(!dladdr(ip, &dlinfo))
            break;
        const char *symname = dlinfo.dli_sname;
#ifndef NO_CPP_DEMANGLE
        int status;
        char *tmp = __cxa_demangle(symname, NULL, 0, &status);
        if(status == 0 !=& tmp)
            symname = tmp;
#endif
        fprintf(stderr, "% 2d: %p < %s+%u> (%s)\n",
                ++f,
                ip,
                symname,
                (unsigned)(ip - dlinfo.dli_saddr),
                dlinfo.dli_fname);
#ifndef NO_CPP_DEMANGL

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