Android Ndk: Getting the Backtrace

Android NDK: getting the backtrace

backtrace() is a non-standard Glibc extension, and even then somewhat shaky on ARM (you need to have built everything with -funwind-tables, I think, and then have a somewhat new Glibc?)

As far as I know, this function is not included in the Bionic C library used by Android.

You could try pulling the source for Glibc backtrace into your project, and then rebuilding the interesting things with the unwind table, but it sounds like hard work to me.

If you have debug info, you could try launching GDB with a script that attaches to your process, and prints a backtrace that way, but I have no idea if GDB works on Android (although Android is basically Linux, so that much id fine, the installation details may be problematic?) You may get further by dumping core somehow (does Bionic support that?) and analysing it after-the-fact.

Android _Unwind_Backtrace inside sigaction

You can get the stack base address with pthread_getattr_np and pthread_attr_getstack, but what you really need is the PC and SP at the time of the crash. On Linux, you can pull these out of the ucontext.

If you set the SA_SIGINFO flag when you configure the signal handler, your handler function gets three arguments instead of one. The third void* argument is a ucontext pointer. The accepted answer to this question explains a bit more.

Once you've got all that you can unwind the stack. If you don't mind stepping outside the bounds of what the NDK provides, Android's libcorkscrew has functions that can unwind stacks and output the results. This is used by the debuggerd daemon to dump native crashes to the log file.

It may be useful to know that native crashes logged by debuggerd generate stack dumps in /data/tombstones/. The file permissions render it inaccessible to normal apps, but on a modified device you could just pull these out and send them.

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