29

我希望堆栈跟踪不仅适用于我的异常,也适用于任何后代std::exception

据我了解,由于堆栈展开(展开)而捕获异常时,堆栈跟踪将完全丢失。

所以我看到抓住它的唯一方法是在std::exception构造函数调用的地方注入代码保存上下文信息(堆栈跟踪)。我对吗?

如果是这样,请告诉我如何在 C++ 中进行代码注入(如果可以的话)。您的方法可能并不完全安全,因为我只需要它用于我的应用程序的调试版本。可能我需要使用汇编程序吗?

我只对 GCC 的解决方案感兴趣。它可以使用 c++0x 特性

4

5 回答 5

40

既然您提到您对特定于 GCC 的东西感到满意,我已经整理了一个示例,说明您可以执行此操作的方式。不过,这纯粹是邪恶的,它插入了 C++ 支持库的内部。我不确定我是否想在生产代码中使用它。反正:

#include <iostream>
#include <dlfcn.h>
#include <execinfo.h>
#include <typeinfo>
#include <string>
#include <memory>
#include <cxxabi.h>
#include <cstdlib>

namespace {
  void * last_frames[20];
  size_t last_size;
  std::string exception_name;

  std::string demangle(const char *name) {
    int status;
    std::unique_ptr<char,void(*)(void*)> realname(abi::__cxa_demangle(name, 0, 0, &status), &std::free);
    return status ? "failed" : &*realname;
  }
}

extern "C" {
  void __cxa_throw(void *ex, void *info, void (*dest)(void *)) {
    exception_name = demangle(reinterpret_cast<const std::type_info*>(info)->name());
    last_size = backtrace(last_frames, sizeof last_frames/sizeof(void*));

    static void (*const rethrow)(void*,void*,void(*)(void*)) __attribute__ ((noreturn)) = (void (*)(void*,void*,void(*)(void*)))dlsym(RTLD_NEXT, "__cxa_throw");
    rethrow(ex,info,dest);
  }
}

void foo() {
  throw 0;
}

int main() {
  try {
    foo();
  }
  catch (...) {
    std::cerr << "Caught a: " << exception_name << std::endl;
    // print to stderr
    backtrace_symbols_fd(last_frames, last_size, 2);
  }
}

我们基本上窃取了对 GCC 用于调度抛出异常的内部实现函数的调用。此时,我们获取堆栈跟踪并将其保存在全局变量中。然后,当我们稍后在 try/catch 中遇到该异常时,我们可以使用堆栈跟踪来打印/保存或您想做的任何事情。我们dlsym()用来查找真实版本的__cxa_throw.

我的示例抛出一个int来证明您可以使用任何类型来执行此操作,而不仅仅是您自己的用户定义的异常。

它使用type_info来获取被抛出的类型的名称,然后对其进行分解。

如果您愿意,可以更好地封装存储堆栈跟踪的全局变量。

我编译并测试了这个:

g++ -Wall -Wextra test.cc -g -O0 -rdynamic -ldl

运行时给出以下内容:

./a.out
抓到一个:int
./a.out(__cxa_throw+0x74)[0x80499be]
./a.out(main+0x0)[0x8049a61]
./a.out(main+0x10)[0x8049a71]
/lib/i686/cmov/libc.so.6(__libc_start_main+0xe6)[0xb75c2ca6]
./a.out[0x80497e1]

不过,请不要将此作为好的建议示例 - 这是您可以通过一些技巧来做的一个示例,并在内部四处寻找!

于 2012-07-26T17:33:16.330 回答
5

在 Linux 上,这可以通过backtrace()在异常构造函数中添加调用来实现,以将堆栈跟踪捕获到异常的成员变量中。不幸的是,它不适用于标准异常,仅适用于您定义的异常。

于 2012-07-26T09:05:38.590 回答
3

几年前我写过这个:Unchaining chained exceptions in C++

基本上,一些宏会记录抛出异常时堆栈展开的位置。

可以在库 Imebra ( http://imebra.com ) 中找到该框架的更新版本。

我会重新实现它的某些部分(比如将堆栈跟踪存储在线程本地存储中)。

于 2012-07-26T09:19:09.473 回答
2

Flexo 的解决方案非常好,而且效果很好。它还具有从回溯地址到过程名称的转换仅在catch部分中执行的好处,因此它取决于异常的接收者是否关心回溯。

然而,在某些情况下,基于 libunwind 的解决方案可能更受欢迎,即因为 libunwind 在某些情况下可以收集backtrace函数无法收集的过程名称。

在这里,我根据 Flexo 的回答提出了一个想法,但有几个扩展。它使用 libunwind 在 throw 时生成回溯,并直接打印到 stderr。它使用 libDL 来识别共享对象文件名。它使用来自 elfutils 的 DWARF 调试信息来收集源代码文件名和行号。它使用 C++ API 来消除 C++ 异常。用户可以设置mExceptionStackTrace变量来临时启用/禁用堆栈跟踪。

关于所有拦截解决方案的重要一点__cxa_throw是,它们可能会增加遍历堆栈的开销。对于我的解决方案尤其如此,它增加了访问调试器符号以收集源文件名的大量开销。这在您希望代码不会抛出的自动测试中可能是可以接受的,并且您希望对抛出的(失败的)测试拥有强大的堆栈跟踪。

// Our stack unwinding is a GNU C extension:
#if defined(__GNUC__)
// include elfutils to parse debugger information:
#include <elfutils/libdwfl.h>

// include libunwind to gather the stack trace:
#define UNW_LOCAL_ONLY
#include <libunwind.h>

#include <dlfcn.h>
#include <cxxabi.h>
#include <typeinfo>
#include <stdio.h>
#include <stdlib.h>

#define LIBUNWIND_MAX_PROCNAME_LENGTH 4096

static bool mExceptionStackTrace = false;


// We would like to print a stacktrace for every throw (even in
// sub-libraries and independent of the object thrown). This works
// only for gcc and only with a bit of trickery
extern "C" {
    void print_exception_info(const std::type_info* aExceptionInfo) {
        int vDemangleStatus;
        char* vDemangledExceptionName;

        if (aExceptionInfo != NULL) {
            // Demangle the name of the exception using the GNU C++ ABI:
            vDemangledExceptionName = abi::__cxa_demangle(aExceptionInfo->name(), NULL, NULL, &vDemangleStatus);
            if (vDemangledExceptionName != NULL) {
                fprintf(stderr, "\n");
                fprintf(stderr, "Caught exception %s:\n", vDemangledExceptionName);

                // Free the memory from __cxa_demangle():
                free(vDemangledExceptionName);
            } else {
                // NOTE: if the demangle fails, we do nothing, so the
                // non-demangled name will be printed. Thats ok.
                fprintf(stderr, "\n");
                fprintf(stderr, "Caught exception %s:\n", aExceptionInfo->name());
            }
        } else {
            fprintf(stderr, "\n");
            fprintf(stderr, "Caught exception:\n");
        }
    }

    void libunwind_print_backtrace(const int aFramesToIgnore) {
        unw_cursor_t vUnwindCursor;
        unw_context_t vUnwindContext;
        unw_word_t ip, sp, off;
        unw_proc_info_t pip;
        int vUnwindStatus, vDemangleStatus, i, n = 0;
        char vProcedureName[LIBUNWIND_MAX_PROCNAME_LENGTH];
        char* vDemangledProcedureName;
        const char* vDynObjectFileName;
        const char* vSourceFileName;
        int vSourceFileLineNumber;

        // This is from libDL used for identification of the object file names:
        Dl_info dlinfo;

        // This is from DWARF for accessing the debugger information:
        Dwarf_Addr addr;
        char* debuginfo_path = NULL;
        Dwfl_Callbacks callbacks = {};
        Dwfl_Line* vDWARFObjLine;


        // initialize the DWARF handling:
        callbacks.find_elf = dwfl_linux_proc_find_elf;
        callbacks.find_debuginfo = dwfl_standard_find_debuginfo;
        callbacks.debuginfo_path = &debuginfo_path;
        Dwfl* dwfl = dwfl_begin(&callbacks);
        if (dwfl == NULL) {
            fprintf(stderr, "libunwind_print_backtrace(): Error initializing DWARF.\n");
        }
        if ((dwfl != NULL) && (dwfl_linux_proc_report(dwfl, getpid()) != 0)) {
            fprintf(stderr, "libunwind_print_backtrace(): Error initializing DWARF.\n");
            dwfl = NULL;
        }
        if ((dwfl != NULL) && (dwfl_report_end(dwfl, NULL, NULL) != 0)) {
            fprintf(stderr, "libunwind_print_backtrace(): Error initializing DWARF.\n");
            dwfl = NULL;
        }


        // Begin stack unwinding with libunwnd:
        vUnwindStatus = unw_getcontext(&vUnwindContext);
        if (vUnwindStatus) {
            fprintf(stderr, "libunwind_print_backtrace(): Error in unw_getcontext: %d\n", vUnwindStatus);
            return;
        }

        vUnwindStatus = unw_init_local(&vUnwindCursor, &vUnwindContext);
        if (vUnwindStatus) {
            fprintf(stderr, "libunwind_print_backtrace(): Error in unw_init_local: %d\n", vUnwindStatus);
            return;
        }

        vUnwindStatus = unw_step(&vUnwindCursor);
        for (i = 0; ((i < aFramesToIgnore) && (vUnwindStatus > 0)); ++i) {
            // We ignore the first aFramesToIgnore stack frames:
            vUnwindStatus = unw_step(&vUnwindCursor);
        }


        while (vUnwindStatus > 0) {
            pip.unwind_info = NULL;
            vUnwindStatus = unw_get_proc_info(&vUnwindCursor, &pip);
            if (vUnwindStatus) {
                fprintf(stderr, "libunwind_print_backtrace(): Error in unw_get_proc_info: %d\n", vUnwindStatus);
                break;
            }

            // Resolve the address of the stack frame using libunwind:
            unw_get_reg(&vUnwindCursor, UNW_REG_IP, &ip);
            unw_get_reg(&vUnwindCursor, UNW_REG_SP, &sp);

            // Resolve the name of the procedure using libunwind:
            // unw_get_proc_name() returns 0 on success, and returns UNW_ENOMEM
            // if the procedure name is too long to fit in the buffer provided and
            // a truncated version of the name has been returned:
            vUnwindStatus = unw_get_proc_name(&vUnwindCursor, vProcedureName, LIBUNWIND_MAX_PROCNAME_LENGTH, &off);
            if (vUnwindStatus == 0) {
                // Demangle the name of the procedure using the GNU C++ ABI:
                vDemangledProcedureName = abi::__cxa_demangle(vProcedureName, NULL, NULL, &vDemangleStatus);
                if (vDemangledProcedureName != NULL) {
                    strncpy(vProcedureName, vDemangledProcedureName, LIBUNWIND_MAX_PROCNAME_LENGTH);
                    // Free the memory from __cxa_demangle():
                    free(vDemangledProcedureName);
                } else {
                    // NOTE: if the demangle fails, we do nothing, so the
                    // non-demangled name will be printed. Thats ok.
                }
            } else if (vUnwindStatus == UNW_ENOMEM) {
                // NOTE: libunwind could resolve the name, but could not store
                // it in a buffer of only LIBUNWIND_MAX_PROCNAME_LENGTH characters.
                // So we have a truncated procedure name that can not be demangled.
                // We ignore the problem and the truncated non-demangled name will
                // be printed.
            } else {
                vProcedureName[0] = '?';
                vProcedureName[1] = '?';
                vProcedureName[2] = '?';
                vProcedureName[3] = 0;
            }


            // Resolve the object file name using dladdr:
            if (dladdr((void *)(pip.start_ip + off), &dlinfo) && dlinfo.dli_fname && *dlinfo.dli_fname) {
                vDynObjectFileName = dlinfo.dli_fname;
            } else {
                vDynObjectFileName = "???";
            }


            // Resolve the source file name using DWARF:
            if (dwfl != NULL) {
                addr = (uintptr_t)(ip - 4);
                Dwfl_Module* module = dwfl_addrmodule(dwfl, addr);
                // Here we could also ask for the procedure name:
                //const char* vProcedureName = dwfl_module_addrname(module, addr);
                // Here we could also ask for the object file name:
                //vDynObjectFileName = dwfl_module_info(module, NULL, NULL, NULL, NULL, NULL, NULL, NULL);
                vDWARFObjLine = dwfl_getsrc(dwfl, addr);
                if (vDWARFObjLine != NULL) {
                    vSourceFileName = dwfl_lineinfo(vDWARFObjLine, &addr, &vSourceFileLineNumber, NULL, NULL, NULL);
                    //fprintf(stderr, " %s:%d", strrchr(vSourceFileName, '/')+1, vSourceFileLineNumber);
                }
            }
            if (dwfl == NULL || vDWARFObjLine == NULL || vSourceFileName == NULL) {
                vSourceFileName = "???";
                vSourceFileLineNumber = 0;
            }


            // Print the stack frame number:
            fprintf(stderr, "#%2d:", ++n);

            // Print the stack addresses:
            fprintf(stderr, " 0x%016" PRIxPTR " sp=0x%016" PRIxPTR, static_cast<uintptr_t>(ip), static_cast<uintptr_t>(sp));

            // Print the source file name:
            fprintf(stderr, " %s:%d", vSourceFileName, vSourceFileLineNumber);

            // Print the dynamic object file name (that is the library name).
            // This is typically not interesting if we have the source file name.
            //fprintf(stderr, " %s", vDynObjectFileName);

            // Print the procedure name:
            fprintf(stderr, " %s", vProcedureName);

            // Print the procedure offset:
            //fprintf(stderr, " + 0x%" PRIxPTR, static_cast<uintptr_t>(off));

            // Print a newline to terminate the output:
            fprintf(stderr, "\n");


            // Stop the stack trace at the main method (there are some
            // uninteresting higher level functions on the stack):
            if (strcmp(vProcedureName, "main") == 0) {
                break;
            }

            vUnwindStatus = unw_step(&vUnwindCursor);
            if (vUnwindStatus < 0) {
                fprintf(stderr, "libunwind_print_backtrace(): Error in unw_step: %d\n", vUnwindStatus);
            }
        }
    }

    void __cxa_throw(void *thrown_exception, std::type_info *info, void (*dest)(void *)) {
        // print the stack trace to stderr:
        if (mExceptionStackTrace) {
            print_exception_info(info);
            libunwind_print_backtrace(1);
        }

        // call the real __cxa_throw():
        static void (*const rethrow)(void*,void*,void(*)(void*)) __attribute__ ((noreturn)) = (void (*)(void*,void*,void(*)(void*)))dlsym(RTLD_NEXT, "__cxa_throw");
        rethrow(thrown_exception,info,dest);
    }
}
#endif
于 2017-07-12T12:15:04.453 回答
0

backward-cpp向后检查它做得很好并且维护得很好

示例代码

在 trace.hxx 中

#define BACKWARD_HAS_DW 1 // or #define BACKWARD_HAS_BFD 1 check docs
#include <backward.hpp>

class recoverable_err final: std::runtime_error
  {
    backward::StackTrace stacktrace_;

  public:
    explicit recoverable_err(std::string msg) noexcept;

    auto
    print_stacktrace(std::ostream &stream)const noexcept -> void;

    [[nodiscard]] auto
    what() const noexcept -> const char * final;
  };

在 trace.cxx 中

  #include "trace.hxx"
  
  recoverable_err::recoverable_err(std::string msg) noexcept
      : std::runtime_error{ msg }
      , stacktrace_{ backward::StackTrace() }
  {
    stacktrace_.load_here();
  }

  auto
  recoverable_err::print_stacktrace(std::ostream &stream)const  noexcept -> void
  {
    using namespace backward;
    Printer p;
    p.object = true;
    p.color_mode = ColorMode::always;
    p.address = true;
    p.print(stacktrace_, stream);
  }

  auto
  recoverable_err::what() const noexcept -> const char *
  {
    return std::runtime_error::what();
  }

主要用途

auto
main() -> int
{
  try
    {
      throw recoverable_err("Recover from nasty error");
    }
  catch (recoverable_err const &ex)
    {
      std::cerr << ex.what();
      ex.print_stacktrace(std::cerr);
    }
  catch (std::exception const &ex)
    {
      std::cerr << "Using default class\n";
      std::cerr << ex.what();
    }
}
于 2021-07-12T22:58:47.773 回答