Breakpad Functioning

This is an Illustration of how Breakpad works.... just to illustrate how the Library behaves etc....

The code I am using is pretty trivial hence the trace etc shall be pretty small newayz....

Here's a simple program that crashes relentlessly :P

include

#include

#include

#include

#include

#include

#include "client/linux/handler/exception_handler.h"

#include "client/linux/handler/linux_thread.h"

using namespace google_breakpad;

static ExceptionHandler* handler_process=NULL;

// Callback when minidump written.

static bool MinidumpCallback(const char *dump_path,

const char *minidump_id,

void *context,

bool succeeded) {

printf("%s is dumped\n", minidump_id);

return true;

}

static void *thread_crash(void *) {

ExceptionHandler handler_process(".", NULL, MinidumpCallback,

NULL, true);

while(true) sleep(1);

}

static void CreateCrashThread() {

pthread_t h;

pthread_create(&h, NULL, thread_crash, NULL);

pthread_detach(h);

}

int main(int argc, char *argv[]) {

int handler_index = 0;

CreateCrashThread();

int *a=NULL;

*a=0; //crash

while (true)

sleep(10);

return 0;

}

What i'll do is compile this code via linking it through the Breakpad Library! I had to compile the code bit by bit.... most of the tools etc were not built by default and were left for( i dunno ) exercise? Newayz......

sanket@sanket-desktop:~/.subversion/google-breakpad-read-only/src/client/linux/handler$ gcc -c -gstabs -I ../../../ myCrash.cc

sanket@sanket-desktop:~/.subversion/google-breakpad-read-only/src/client/linux/handler$ g++ -gstabs -lpthread myCrash.o exception_handler.o linux_thread.o minidump_generator.o ../../minidump_file_writer.o ../../../common/convert_UTF.o ../../../common/string_conversion.o ../../../common/linux/file_id.o ../../../common/linux/guid_creator.o md5.o -o output

sanket@sanket-desktop:~/.subversion/google-breakpad-read-only/src/client/linux/handler$ ./output

5012fabe-5cd6-0ede-35eb05fb-77e2564c is dumped

sanket@sanket-desktop:~/.subversion/google-breakpad-read-only/src/client/linux/handler$ ls -lh 5012fabe-5cd6-0ede-35eb05fb-77e2564c.dmp

-rw------- 1 sanket sanket 18K 2009-03-30 16:55 5012fabe-5cd6-0ede-35eb05fb-77e2564c.dmp

Hence we have a dump which will invariably be of size of 10-20 Kb. There can be optimization here based on local processing so as to reduce server load... but i'll defer from treating that topic here :)

The important thing is the generation of meaningful data from this dump. As I have used the normal libs( libstdc++ etc ) which dont have symbol information the output might not be that well percieved;

sanket@sanket-desktop:~/.subversion/google-breakpad-read-only/src/tools/linux/dump_syms$ ./dump_syms ../../../client/linux/handler/myCrash.o > myCrashSyms.sym

There's a python code which i searched and it's pretty good when creating Symbols from files in a very systematic File Hierarchy i shall use that code as a Part of a larger project that might need more tweaking... here's the link..

http://crashopensource.files.wordpress.com/2007/12/symbolstore12_07_2007.txt

Continuing i shall show you the result after running minidump_stackwalk on the minidump file along with the symbols file we just created:

Here's the o/p when run with minidump_stackwalk bin.

------------------------------------------------------------------------------------------------------------------------

Operating system: Linux

0.0.0 Linux 2.6.27-11-generic #1 SMP Thu Jan 29 19:24:39 UTC 2009 i686 GNU/Linux

CPU: x86

GenuineIntel family 6 model 6 stepping 5

2 CPUs

Crash reason: SIGSEGV

Crash address: 0x80497d1

Thread 0 (crashed)

0 output + 0x17d1

eip = 0x080497d1 esp = 0xbfe87360 ebp = 0xbfe87378 ebx = 0xb7e14ff4

esi = 0x08053650 edi = 0x080496c0 eax = 0x00000000 ecx = 0x00005045

edx = 0xb7cb9b90 efl = 0x00010246

1 libc-2.8.90.so + 0x16684

eip = 0xb7cd1685 esp = 0xbfe87380 ebp = 0xbfe873e8

Thread 1

0 0xb7f87430

eip = 0xb7f87430 esp = 0xb7cb6d50 ebp = 0xb7cb6f28 ebx = 0xb7cb6f14

esi = 0xb7cb6f14 edi = 0xb7cb6f14 eax = 0xfffffdfc ecx = 0xb7cb6f14

edx = 0xb7e14ff4 efl = 0x00000246

1 output + 0x1929

eip = 0x0804992a esp = 0xb7cb6f30 ebp = 0xb7cb93b8

2 libpthread-2.8.90.so + 0x650e

eip = 0xb7f4350f esp = 0xb7cb93c0 ebp = 0xb7cb94b8

Loaded modules:

0x08048000 - 0x08056fff output ??? (main)

0x08057000 - 0x08057fff output ???

0x08058000 - 0x08058fff output ???

0xb7cbb000 - 0xb7e12fff libc-2.8.90.so ???

0xb7e13000 - 0xb7e14fff libc-2.8.90.so ???

0xb7e15000 - 0xb7e15fff libc-2.8.90.so ???

0xb7e19000 - 0xb7e25fff libgcc_s.so.1 ???

0xb7e26000 - 0xb7e26fff libgcc_s.so.1 ???

0xb7e27000 - 0xb7e27fff libgcc_s.so.1 ???

0xb7e28000 - 0xb7e4bfff libm-2.8.90.so ???

0xb7e4c000 - 0xb7e4cfff libm-2.8.90.so ???

0xb7e4d000 - 0xb7e4dfff libm-2.8.90.so ???

0xb7e4f000 - 0xb7f31fff libstdc++.so.6.0.10 ???

0xb7f32000 - 0xb7f35fff libstdc++.so.6.0.10 ???

0xb7f36000 - 0xb7f36fff libstdc++.so.6.0.10 ???

0xb7f3d000 - 0xb7f51fff libpthread-2.8.90.so ???

0xb7f52000 - 0xb7f52fff libpthread-2.8.90.so ???

0xb7f53000 - 0xb7f53fff libpthread-2.8.90.so ???

0xb7f6d000 - 0xb7f86fff ld-2.8.90.so ???

0xb7f88000 - 0xb7f88fff ld-2.8.90.so ???

0xb7f89000 - 0xb7f89fff ld-2.8.90.so ???

------------------------------------------------------------------------------------------------------------------------

It sums it all.... we can now start creating symbol compiled library and compile them with -gstabs etc to produce the appropriate symbols etc.

Chao :-)