libunwind-examples

This repo is just a bunch of tools and test code to help understand the behaviour of libunwind.

• unwind-pid - remote unwind example that uses ptrace to unwind the
  stack of an alien process, identified by PID
• unwind-local - local unwind example

Thanks to Eli Bendersky, whose blog post on libunwind is easy to find with a search engine and whose example code was a great help to get started.

Tests

The tests in this repo are not a full test suite, just a couple of simple smoke tests that check unwinding into, out of and through the (dynamically linked) C library.

test-bsearch has a stack the originates in application code, but whose stack includes a C library function before we reach main.

sh$ ./test-bsearch &
[1] 13219
sh$ ./unwind-pid $!
0x400502: (cmp+0xc)
0x7fb4de093677: (bsearch+0x57)
0x400556: (main+0x52)
0x7fb4de07c401: (__libc_start_main+0xf1)
0x40042a: (_start+0x2a)
sh$ kill %1
[1]+  Terminated              ./test-bsearch

test-cxx is quick test that shows backtracing out of C++ code. There is no dynamic link coverage in this test (all library code used is template instantiated).

linaro-alip$ ./test-cxx & p=$!; sleep 0.1; ./unwind-pid $p; kill $p
[1] 26683
0xaaaab96b6a3c:
(_ZNSt23mersenne_twister_engineImLm32ELm624ELm397ELm31ELm2567483615ELm11ELm4294967295ELm7ELm2636928640ELm15ELm4022730752ELm18ELm1812433253EEclEv+0xec)

0xaaaab96b6aa8: (_ZNSt24uniform_int_distributionIiEclISt23mersenne_twister_engineImLm32ELm624ELm397ELm31ELm2567483615ELm11ELm4294967295ELm7ELm2636928640ELm15ELm4022730752ELm18ELm1812433253EEEEiRT_RKNS0_10param_typeE+0x50) 0xaaaab96b6804: (main+0x28) 0xffffadeb5364: (__libc_start_main+0xdc) 0xffffadeb5364: (__libc_start_main+0xdc) [1]+ Terminated ./test-cxx

test-sleep has a stack that originates in the C library code to make a system call.

sh$ ./test-sleep &
[1] 13224
sh$ ./unwind-pid $!
0x7f5f3329a7b0: (__nanosleep_nocancel+0x7)
0x7f5f3329a71a: (sleep+0x2a)
0x40050f: (main+0x19)
0x7f5f331ee401: (__libc_start_main+0xf1)
0x40042a: (_start+0x2a)
sh$ kill %1
[1]+  Terminated              ./test-sleep

test-strlen has a stack that originates in regular C library code.

sh$ ./test-strlen &
[1] 13240
sh$ ./unwind-pid $!
0x7ffb6c47f09f: (strlen+0x13f)
0x4005c3: (main+0x2d)
0x7ffb6c412401: (__libc_start_main+0xf1)
0x4004ca: (_start+0x2a)
sh$ kill %1
sh$ 
[1]+  Terminated              ./test-strlen