C display stack trace on exception

Question

I want to have a way to report the stack trace to the user if an exception is thrown  What is the best way to do this  Does it take huge amounts of extra code   To answer questions   I d like it to be portable if possible  I want information to pop up  so the user can copy the stack trace and email it to me if an error comes up

User · Answer

Since the stack is already unwound when entering the catch block, the solution in my case was to not catch certain exceptions which then lead to a SIGABRT. In the signal handler for SIGABRT I then fork() and execl() either gdb (in debug builds) or Google breakpads stackwalk (in release builds). Also I try to only use signal handler safe functions.

GDB:

static const char BACKTRACE_START[] = "<2>--- backtrace of entire stack ---\n";
static const char BACKTRACE_STOP[] = "<2>--- backtrace finished ---\n";

static char *ltrim(char *s)
{
    while (' ' == *s) {
        s++;
    }
    return s;
}

void Backtracer::print()
{
    int child_pid = ::fork();
    if (child_pid == 0) {
        // redirect stdout to stderr
        ::dup2(2, 1);

        // create buffer for parent pid (2+16+1 spaces to allow up to a 64 bit hex parent pid)
        char pid_buf[32];
        const char* stem = "                   ";
        const char* s = stem;
        char* d = &pid_buf[0];
        while (static_cast<bool>(*s))
        {
            *d++ = *s++;
        }
        *d-- = '\0';
        char* hexppid = d;

        // write parent pid to buffer and prefix with 0x
        int ppid = getppid();
        while (ppid != 0) {
            *hexppid = ((ppid & 0xF) + '0');
            if(*hexppid > '9') {
                *hexppid += 'a' - '0' - 10;
            }
            --hexppid;
            ppid >>= 4;
        }
        *hexppid-- = 'x';
        *hexppid = '0';

        // invoke GDB
        char name_buf[512];
        name_buf[::readlink("/proc/self/exe", &name_buf[0], 511)] = 0;
        ssize_t r = ::write(STDERR_FILENO, &BACKTRACE_START[0], sizeof(BACKTRACE_START));
        (void)r;
        ::execl("/usr/bin/gdb",
                "/usr/bin/gdb", "--batch", "-n", "-ex", "thread apply all bt full", "-ex", "quit",
                &name_buf[0], ltrim(&pid_buf[0]), nullptr);
        ::exit(1); // if GDB failed to start
    } else if (child_pid == -1) {
        ::exit(1); // if forking failed
    } else {
        // make it work for non root users
        if (0 != getuid()) {
            ::prctl(PR_SET_PTRACER, PR_SET_PTRACER_ANY, 0, 0, 0);
        }
        ::waitpid(child_pid, nullptr, 0);
        ssize_t r = ::write(STDERR_FILENO, &BACKTRACE_STOP[0], sizeof(BACKTRACE_STOP));
        (void)r;
    }
}

minidump_stackwalk:

static bool dumpCallback(const google_breakpad::MinidumpDescriptor& descriptor, void* context, bool succeeded)
{
    int child_pid = ::fork();
    if (child_pid == 0) {
        ::dup2(open("/dev/null", O_WRONLY), 2); // ignore verbose output on stderr
        ssize_t r = ::write(STDOUT_FILENO, &MINIDUMP_STACKWALK_START[0], sizeof(MINIDUMP_STACKWALK_START));
        (void)r;
        ::execl("/usr/bin/minidump_stackwalk", "/usr/bin/minidump_stackwalk", descriptor.path(), "/usr/share/breakpad-syms", nullptr);
        ::exit(1); // if minidump_stackwalk failed to start
    } else if (child_pid == -1) {
        ::exit(1); // if forking failed
    } else {
        ::waitpid(child_pid, nullptr, 0);
        ssize_t r = ::write(STDOUT_FILENO, &MINIDUMP_STACKWALK_STOP[0], sizeof(MINIDUMP_STACKWALK_STOP));
        (void)r;
    }
    ::remove(descriptor.path()); // this is not signal safe anymore but should still work
    return succeeded;
}

Edit: To make it work for breakpad I also had to add this:

std::set_terminate([]()
{
    ssize_t r = ::write(STDERR_FILENO, EXCEPTION, sizeof(EXCEPTION));
    (void)r;
    google_breakpad::ExceptionHandler::WriteMinidump(std::string("/tmp"), dumpCallback, NULL);
    exit(1); // avoid creating a second dump by not calling std::abort
});

Source: How to get a stack trace for C++ using gcc with line number information? and Is it possible to attach gdb to a crashed process (a.k.a "just-in-time" debugging)

User · Answer

on linux with g   check out this lib  https   sourceforge net projects libcsdbg  it does all the work for you

User · Answer

I would like to add a standard library option  i e  cross-platform  how to generate exception backtraces  which has become available with C  11   Use std  nested exception and std  throw with nested  This won t give you a stack unwind  but in my opinion the next best thing  It is described on StackOverflow here and here  how you can get a backtrace on your exceptions inside your code without need for a debugger or cumbersome logging  by simply writing a proper exception handler which will rethrow nested exceptions   Since you can do this with any derived exception class  you can add a lot of information to such a backtrace  You may also take a look at my MWE on GitHub  where a backtrace would look something like this   Library API  Exception caught in function  api function  Backtrace    Git mwe-cpp-exception src detail Library cpp 17   library function failed   Git mwe-cpp-exception src detail Library cpp 13   could not open file  nonexistent txt

User · Answer

Poppy can gather not only the stack trace  but also parameter values  local variables  etc  - everything leading to the crash

User · Answer

I have a similar problem  and though I like portability  I only need gcc support   In gcc  execinfo h and the backtrace calls are available   To demangle the function names  Mr  Bingmann has a nice piece of code  To dump a backtrace on an exception  I create an exception that prints the backtrace in the constructor   If I were expecting this to work with an exception thrown in a library  it might require rebuilding linking so that the backtracing exception is used                                                Makefile with flags for printing backtrace with function names   compile with symbols for backtrace CXXFLAGS -g   add symbols to dynamic symbol table for backtrace LDFLAGS -rdynamic turducken  turducken cc                                               include  lt cstdio gt   include  lt stdexcept gt   include  lt execinfo h gt   include  stacktrace h     https   panthema net 2008 0901-stacktrace-demangled         simple exception that prints backtrace when constructed class btoverflow error  public std  overflow error       public      btoverflow error  const std  string amp  arg             std  overflow error  arg                 print stacktrace                void chicken void        throw btoverflow error   too big        void duck void        chicken       void turkey void        duck       int main  int argc  char  argv          try               turkey              catch  btoverflow error e                printf   caught exception   s n   e what                Compiling and running this with gcc 4 8 4 yields a backtrace with nicely unmangled C   function names   stack trace     turducken   btoverflow error  btoverflow error std  string const amp   0x43    turducken   chicken   0x48    turducken   duck   0x9    turducken   turkey   0x9    turducken   main   0x15   lib x86 64-linux-gnu libc so 6     libc start main   0xf5    turducken    0x401629

User · Answer

The following code stops the execution right after an exception is thrown  You need to set a windows exception handler along with a termination handler   I tested this in MinGW 32bits    void beforeCrash void    static const bool SET TERMINATE   std  set terminate beforeCrash    void beforeCrash           asm  int3       int main int argc  char  argv      SetUnhandledExceptionFilter windows exception handler           Check the following code for the windows exception handler function  http   www codedisqus com 0ziVPgVPUk exception-handling-and-stacktrace-under-windows-mingwgcc html

User · Answer

AFAIK libunwind is quite portable and so far I haven t found anything easier to use

User · Answer

I recommend http   stacktrace sourceforge net  project  It support Windows  Mac OS and also Linux

User · Answer

On Windows  check out BugTrap  Its not longer at the original link  but its still available on CodeProject

User · Answer

If you are using C   and don t want can t use Boost  you can print backtrace with demangled names using the following code  link to the original site    Note  this solution is specific to Linux  It uses GNU s libc functions backtrace   backtrace symbols    from execinfo h  to get the backtraces and then uses   cxa demangle    from cxxabi h  for demangling the backtrace symbol names      stacktrace h  c  2008  Timo Bingmann from http   idlebox net     published under the WTFPL v2 0   ifndef  STACKTRACE H   define  STACKTRACE H    include  lt stdio h gt   include  lt stdlib h gt   include  lt execinfo h gt   include  lt cxxabi h gt       Print a demangled stack backtrace of the caller function to FILE  out     static inline void print stacktrace FILE  out   stderr  unsigned int max frames   63        fprintf out   stack trace  n            storage array for stack trace address data     void  addrlist max frames 1           retrieve current stack addresses     int addrlen   backtrace addrlist  sizeof addrlist    sizeof void          if  addrlen    0        fprintf out      lt empty  possibly corrupt gt  n        return                resolve addresses into strings containing  filename function address           this array must be free  -ed     char   symbollist   backtrace symbols addrlist  addrlen           allocate string which will be filled with the demangled function name     size t funcnamesize   256      char  funcname    char  malloc funcnamesize           iterate over the returned symbol lines  skip the first  it is the        address of this function      for  int i   1  i  lt  addrlen  i              char  begin name   0   begin offset   0   end offset   0          find parentheses and  address offset surrounding the mangled name           module function 0x15c   0x8048a6d      for  char  p   symbollist i    p    p                if   p                 begin name   p          else if   p                 begin offset   p          else if   p         amp  amp  begin offset            end offset   p          break                       if  begin name  amp  amp  begin offset  amp  amp  end offset          amp  amp  begin name  lt  begin offset                 begin name       0            begin offset       0            end offset     0               mangled name is now in  begin name  begin offset  and caller            offset in  begin offset  end offset   now apply              cxa demangle             int status          char  ret   abi    cxa demangle begin name                          funcname   amp funcnamesize   amp status           if  status    0            funcname   ret     use possibly realloc  -ed string         fprintf out      s    s  s n               symbollist i   funcname  begin offset                     else              demangling failed  Output function name as a C function with            no arguments          fprintf out      s    s    s n               symbollist i   begin name  begin offset                       else                  couldn t parse the line  print the whole line          fprintf out      s n   symbollist i                     free funcname       free symbollist       endif     STACKTRACE H    HTH

User · Answer

If you are using Boost 1 65 or higher  you can use boost  stacktrace    include  lt boost stacktrace hpp gt          somewhere inside the bar int  function that is called recursively  std  cout  lt  lt  boost  stacktrace  stacktrace

User · Answer

Andrew Grant s answer does not help getting a stack trace of the throwing function  at least not with GCC  because a throw statement does not save the current stack trace on its own  and the catch handler won t have access to the stack trace at that point any more   The only way - using GCC - to solve this is to make sure to generate a stack trace at the point of the throw instruction  and save that with the exception object   This method requires  of course  that every code that throws an exception uses that particular Exception class   Update 11 July 2017  For some helpful code  take a look at cahit beyaz s answer  which points to http   stacktrace sourceforge net - I haven t used it yet but it looks promising

User · Answer

A working example for OSX  tested right now on Catalina 10 15   Not portable to linux windows obviously  Probably it will be usefull to somebody  In the  quot Mew-exception quot  string you can use backtrace and or backtrace symbols functions  include  lt stdexcept gt   include  lt typeinfo gt   include  lt dlfcn h gt   extern  quot C quot  void   cxa throw void  thrown object  std  type info  tinfo  void   dest  void      static void     cxa throw orig  void  thrown object  std  type info  tinfo  void   dest  void      extern  quot C quot  void luna cxa throw void  thrown object  std  type info  tinfo  void   dest  void           printf  quot Mew-exception you can catch your backtrace here  quot          cxa throw orig thrown object  tinfo  dest           attribute     used       attribute     section   quot   DATA   interpose quot     static struct replace pair t       void  replacement   replacee    replace pair      void  luna cxa throw   void    cxa throw     extern  quot C quot  const struct mach header   dso handle  extern  quot C quot  void dyld dynamic interpose const struct mach header                                  const replace pair t replacements                                   size t count    int fn         int a   10    a      throw std  runtime error  quot Mew  quot       int main int argc  const char   argv            cxa throw orig    void     void  thrown object  std  type info  tinfo  void   dest  void     dlsym RTLD DEFAULT   quot   cxa throw quot         dyld dynamic interpose  amp   dso handle   amp replace pair  1        fn        return 0

User · Answer

Unix   backtrace  Mac   backtrace  Windows  CaptureBackTrace

User · Answer

It depends which platform    On GCC it s pretty trivial  see this post for more details   On MSVC then you can use the StackWalker library that handles all of the underlying API calls needed for Windows   You ll have to figure out the best way to integrate this functionality into your app  but the amount of code you need to write should be minimal

User · Answer

Cpp-tool ex diag - easyweight  multiplatform  minimal resource using  simple and flexible at trace

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