c++ - Android NDK: getting the backtrace

Question

I'm developing the native application that works with Android via the NDK. I need to call the backtrace() function when there is a crash. The problem is that there is no <execinfo.h> for the NDK.

Is there any other way to get that back trace?

Answer 1

Android have no backtrace(), but unwind.h is here to serve. Symbolization is possible via dladdr().

The following code is my simple implementation of backtrace (with no demangling):

#include <iostream>
#include <iomanip>

#include <unwind.h>
#include <dlfcn.h>

namespace {

struct BacktraceState
{
    void** current;
    void** end;
};

static _Unwind_Reason_Code unwindCallback(struct _Unwind_Context* context, void* arg)
{
    BacktraceState* state = static_cast<BacktraceState*>(arg);
    uintptr_t pc = _Unwind_GetIP(context);
    if (pc) {
        if (state->current == state->end) {
            return _URC_END_OF_STACK;
        } else {
            *state->current++ = reinterpret_cast<void*>(pc);
        }
    }
    return _URC_NO_REASON;
}

}

size_t captureBacktrace(void** buffer, size_t max)
{
    BacktraceState state = {buffer, buffer + max};
    _Unwind_Backtrace(unwindCallback, &state);

    return state.current - buffer;
}

void dumpBacktrace(std::ostream& os, void** buffer, size_t count)
{
    for (size_t idx = 0; idx < count; ++idx) {
        const void* addr = buffer[idx];
        const char* symbol = "";

        Dl_info info;
        if (dladdr(addr, &info) && info.dli_sname) {
            symbol = info.dli_sname;
        }

        os << "  #" << std::setw(2) << idx << ": " << addr << "  " << symbol << "
";
    }
}

It may be used for backtracing into LogCat like

#include <sstream>
#include <android/log.h>

void backtraceToLogcat()
{
    const size_t max = 30;
    void* buffer[max];
    std::ostringstream oss;

    dumpBacktrace(oss, buffer, captureBacktrace(buffer, max));

    __android_log_print(ANDROID_LOG_INFO, "app_name", "%s", oss.str().c_str());
}