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