How to get a stack trace for C++ using gcc with li

Question

We use stack traces in proprietary assert like macro to catch developer mistakes - when error is caught, stack trace is printed.

I find gcc's pair backtrace()/backtrace_symbols() methods insufficient:

1. Names are mangled
2. No line information

1st problem can be resolved by abi::__cxa_demangle.

However 2nd problem s more tough. I found replacement for backtrace_symbols(). This is better than gcc's backtrace_symbols(), since it can retrieve line numbers (if compiled with -g) and you don't need to compile with -rdynamic.

Hoverer the code is GNU licenced, so IMHO I can't use it in commercial code.

Any proposal?

P.S.

gdb is capable to print out arguments passed to functions. Probably it's already too much to ask for :)

PS 2

Similar question (thanks nobar)

Answer 1

Here's an alternative approach. A debug_assert() macro programmatically sets a conditional breakpoint. If you are running in a debugger, you will hit a breakpoint when the assert expression is false -- and you can analyze the live stack (the program doesn't terminate). If you are not running in a debugger, a failed debug_assert() causes the program to abort and you get a core dump from which you can analyze the stack (see my earlier answer).

The advantage of this approach, compared to normal asserts, is that you can continue running the program after the debug_assert is triggered (when running in a debugger). In other words, debug_assert() is slightly more flexible than assert().

   #include <iostream>
   #include <cassert>
   #include <sys/resource.h> 

// note: The assert expression should show up in
// stack trace as parameter to this function
void debug_breakpoint( char const * expression )
   {
   asm("int3"); // x86 specific
   }

#ifdef NDEBUG
   #define debug_assert( expression )
#else
// creates a conditional breakpoint
   #define debug_assert( expression ) \
      do { if ( !(expression) ) debug_breakpoint( #expression ); } while (0)
#endif

void recursive( int i=0 )
   {
   debug_assert( i < 5 );
   if ( i < 10 ) recursive(i+1);
   }

int main( int argc, char * argv[] )
   {
   rlimit core_limit = { RLIM_INFINITY, RLIM_INFINITY };
   setrlimit( RLIMIT_CORE, &core_limit ); // enable core dumps
   recursive();
   }

Note: Sometimes "conditional breakpoints" setup within debuggers can be slow. By establishing the breakpoint programmatically, the performance of this method should be equivalent to that of a normal assert().

Note: As written, this is specific to the Intel x86 architecture -- other processors may have different instructions for generating a breakpoint.

Answer 2

here is my solution:

#include <execinfo.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <stdlib.h>
#include <iostream>
#include <zconf.h>
#include "regex"

std::string getexepath() {
    char result[PATH_MAX];
    ssize_t count = readlink("/proc/self/exe", result, PATH_MAX);
    return std::string(result, (count > 0) ? count : 0);
}

std::string sh(std::string cmd) {
    std::array<char, 128> buffer;
    std::string result;
    std::shared_ptr<FILE> pipe(popen(cmd.c_str(), "r"), pclose);
    if (!pipe) throw std::runtime_error("popen() failed!");
    while (!feof(pipe.get())) {
        if (fgets(buffer.data(), 128, pipe.get()) != nullptr) {
            result += buffer.data();
        }
    }
    return result;
}


void print_backtrace(void) {
    void *bt[1024];
    int bt_size;
    char **bt_syms;
    int i;

    bt_size = backtrace(bt, 1024);
    bt_syms = backtrace_symbols(bt, bt_size);
    std::regex re("\\[(.+)\\]");
    auto exec_path = getexepath();
    for (i = 1; i < bt_size; i++) {
        std::string sym = bt_syms[i];
        std::smatch ms;
        if (std::regex_search(sym, ms, re)) {
            std::string addr = ms[1];
            std::string cmd = "addr2line -e " + exec_path + " -f -C " + addr;
            auto r = sh(cmd);
            std::regex re2("\\n$");
            auto r2 = std::regex_replace(r, re2, "");
            std::cout << r2 << std::endl;
        }
    }
    free(bt_syms);
}

void test_m() {
    print_backtrace();
}

int main() {
    test_m();
    return 0;
}

output:

/home/roroco/Dropbox/c/ro-c/cmake-build-debug/ex/test_backtrace_with_line_number
test_m()
/home/roroco/Dropbox/c/ro-c/ex/test_backtrace_with_line_number.cpp:57
main
/home/roroco/Dropbox/c/ro-c/ex/test_backtrace_with_line_number.cpp:61
??
??:0

"??" and "??:0" since this trace is in libc, not in my source

Answer 3

Use the google glog library for it. It has new BSD licence.

It contains a GetStackTrace function in the stacktrace.h file.

EDIT

I found here http://blog.bigpixel.ro/2010/09/09/stack-unwinding-stack-trace-with-gcc/ that there is an utility called addr2line that translates program addresses into file names and line numbers.

http://linuxcommand.org/man_pages/addr2line1.html

Answer 4

The one of solutions is to start a gdb with "bt"-script in failed assert handler. It is not very easy to integrate such gdb-starting, but It will give you both backtrace and args and demangle names (or you can pass gdb output via c++filt programm).

Both programms (gdb and c++filt) will be not linked into your application, so GPL will not require you to opensource complete application.

The same approach (exec a GPL programme) you can use with backtrace-symbols. Just generate ascii list of %eip's and map of exec file (/proc/self/maps) and pass it to separate binary.

Answer 5

You can use DeathHandler - small C++ class which does everything for you, reliable.

Answer 6

So you want a stand-alone function that prints a stack trace with all of the features that gdb stack traces have and that doesn't terminate your application. The answer is to automate the launch of gdb in a non-interactive mode to perform just the tasks that you want.

This is done by executing gdb in a child process, using fork(), and scripting it to display a stack-trace while your application waits for it to complete. This can be performed without the use of a core-dump and without aborting the application. I learned how to do this from looking at this question: How it's better to invoke gdb from program to print it's stacktrace?

The example posted with that question didn't work for me exactly as written, so here's my "fixed" version (I ran this on Ubuntu 9.04).

#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
#include <unistd.h>

void print_trace() {
    char pid_buf[30];
    sprintf(pid_buf, "%d", getpid());
    char name_buf[512];
    name_buf[readlink("/proc/self/exe", name_buf, 511)]=0;
    int child_pid = fork();
    if (!child_pid) {           
        dup2(2,1); // redirect output to stderr
        fprintf(stdout,"stack trace for %s pid=%s\n",name_buf,pid_buf);
        execlp("gdb", "gdb", "--batch", "-n", "-ex", "thread", "-ex", "bt", name_buf, pid_buf, NULL);
        abort(); /* If gdb failed to start */
    } else {
        waitpid(child_pid,NULL,0);
    }
}

As shown in the referenced question, gdb provides additional options that you could use. For example, using "bt full" instead of "bt" produces an even more detailed report (local variables are included in the output). The manpages for gdb are kind of light, but complete documentation is available here.

Since this is based on gdb, the output includes demangled names, line-numbers, function arguments, and optionally even local variables. Also, gdb is thread-aware, so you should be able to extract some thread-specific metadata.

Here's an example of the kind of stack traces that I see with this method.

0x00007f97e1fc2925 in waitpid () from /lib/libc.so.6
[Current thread is 0 (process 15573)]
#0  0x00007f97e1fc2925 in waitpid () from /lib/libc.so.6
#1  0x0000000000400bd5 in print_trace () at ./demo3b.cpp:496
2  0x0000000000400c09 in recursive (i=2) at ./demo3b.cpp:636
3  0x0000000000400c1a in recursive (i=1) at ./demo3b.cpp:646
4  0x0000000000400c1a in recursive (i=0) at ./demo3b.cpp:646
5  0x0000000000400c46 in main (argc=1, argv=0x7fffe3b2b5b8) at ./demo3b.cpp:70

Note: I found this to be incompatible with the use of valgrind (probably due to Valgrind's use of a virtual machine). It also doesn't work when you are running the program inside of a gdb session (can't apply a second instance of "ptrace" to a process).