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我的问题与其他询问故障地址的问题有些不同。我正在尝试实现一个可怕的黑客攻击，以确定信号是否中断了系统调用或普通用户代码，方法是检查保存的指令指针处的代码并将其与主机架构可能的系统调用入口指令进行比较继续运行。这是实现正确的 POSIX 线程取消的一部分，它不受我的旧问题中描述的竞争条件和资源泄漏的影响：

POSIX 取消点应该如何表现？

如果这种方法不可靠或有其他错误，我也想听听原因。

4

1 回答 1

16 
/* sigsegv.c */
/**
 * This source file is used to print out a stack-trace when your program
 * segfaults. It is relatively reliable and spot-on accurate.
 *
 * This code is in the public domain. Use it as you see fit, some credit
 * would be appreciated, but is not a prerequisite for usage. Feedback
 * on it's use would encourage further development and maintenance.
 *
 * Due to a bug in gcc-4.x.x you currently have to compile as C++ if you want
 * demangling to work.
 *
 * Please note that it's been ported into my ULS library, thus the check for
 * HAS_ULSLIB and the use of the sigsegv_outp macro based on that define.
 *
 * Author: Jaco Kroon <jaco@kroon.co.za>
 *
 * Copyright (C) 2005 - 2010 Jaco Kroon
 */
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif

/* Bug in gcc prevents from using CPP_DEMANGLE in pure "C" */
#if !defined(__cplusplus) && !defined(NO_CPP_DEMANGLE)
#define NO_CPP_DEMANGLE
#endif

#include <memory.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <signal.h>
#include <ucontext.h>
#include <dlfcn.h>
#ifndef NO_CPP_DEMANGLE
#include <cxxabi.h>
#ifdef __cplusplus
using __cxxabiv1::__cxa_demangle;
#endif
#endif

#ifdef HAS_ULSLIB
#include "uls/logger.h"
#define sigsegv_outp(x)         sigsegv_outp(,gx)
#else
#define sigsegv_outp(x, ...)    fprintf(stderr, x "\n", ##__VA_ARGS__)
#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"};

    int i, f = 0;
    ucontext_t *ucontext = (ucontext_t*)ptr;
    Dl_info dlinfo;
    void **bp = 0;
    void *ip = 0;

    sigsegv_outp("Segmentation Fault!");
    sigsegv_outp("info.si_signo = %d", signum);
    sigsegv_outp("info.si_errno = %d", info->si_errno);
    sigsegv_outp("info.si_code  = %d (%s)", info->si_code, si_codes[info->si_code]);
    sigsegv_outp("info.si_addr  = %p", info->si_addr);
    for(i = 0; i < NGREG; i++)
        sigsegv_outp("reg[%02d]       = 0x" REGFORMAT, i, ucontext->uc_mcontext.gregs[i]);

#ifndef SIGSEGV_NOSTACK
#if defined(SIGSEGV_STACK_IA64) || defined(SIGSEGV_STACK_X86)
#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

    sigsegv_outp("Stack trace:");
    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

        sigsegv_outp("% 2d: %p <%s+%lu> (%s)",
                 ++f,
                 ip,
                 symname,
                 (unsigned long)ip - (unsigned long)dlinfo.dli_saddr,
                 dlinfo.dli_fname);

#ifndef NO_CPP_DEMANGLE
        if (tmp)
            free(tmp);
#endif

        if(dlinfo.dli_sname && !strcmp(dlinfo.dli_sname, "main"))
            break;

        ip = bp[1];
        bp = (void**)bp[0];
    }
#else
    sigsegv_outp("Stack trace (non-dedicated):");
    sz = backtrace(bt, 20);
    strings = backtrace_symbols(bt, sz);
    for(i = 0; i < sz; ++i)
        sigsegv_outp("%s", strings[i]);
#endif
    sigsegv_outp("End of stack trace.");
#else
    sigsegv_outp("Not printing stack strace.");
#endif
    _exit (-1);
}

static void __attribute__((constructor)) setup_sigsegv() {
    struct sigaction action;
    memset(&action, 0, sizeof(action));
    action.sa_sigaction = signal_segv;
    action.sa_flags = SA_SIGINFO;
    if(sigaction(SIGSEGV, &action, NULL) < 0)
        perror("sigaction");
}

$ g++ -fPIC -shared -o libsigsegv.so -ldl sigsegv

$ export LD_PRELOAD=/path/to/libsigsegv.so

我在 LUG 上找到了这个代码。无法访问指向此处 URL 的页面，因此粘贴了整个代码。当 SIGSEGV 发生时，此代码会打印一个小的堆栈跟踪。不确定是否有其他方式不使用 ucontext_t。

于 2011-03-24T22:19:34.187 回答