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AddressSanitizerCallStack

Alexander Potapenko edited this page Dec 2, 2015 · 3 revisions

AddressSanitizer collects call stacks on the following events:

  • malloc and free
  • thread creation
  • failure

malloc and free happen relatively frequently and it is important to unwind the call stack fast. AddressSanitizer uses a simple unwinder that relies on frame pointers.

If you don't care about malloc/free call stacks, simply disable the unwinder completely (use malloc_context_size=0 runtime flag).

Each stack frame needs to be symbolized (of course, if the binary is compiled with debug info). Given a PC, we need to print

  #0xabcdf function_name file_name.cc:1234

AddressSanitizer uses llvm-symbolizer binary from the Clang distribution to symbolize the stack traces (note that ideally the llvm-symbolizer version must match the version of ASan runtime library). Just make sure llvm-symbolizer is in PATH before running the binary or provide it in separate ASAN_SYMBOLIZER_PATH environment variable:

export ASAN_SYMBOLIZER_PATH=/path/to/llvm_build/bin/llvm-symbolizer
./a.out

If you want to disable symbolization for some reason, you may do so by providing empty string as ASAN_SYMBOLIZER_PATH value:

ASAN_SYMBOLIZER_PATH= ./a.out

You may also filter the log file through scripts/asan_symbolize.py to get the symbols. This script takes an optional parameter -- a file prefix. The substring .*prefix will be removed from the file names.

% ./a.out
    ...
    #0 0x402c77 (/home/you/address-sanitizer/asan/a.out+0x402c77)
    ...
% ./a.out 2>&1  | ../scripts/asan_symbolize.py
   ...
   #0 0x402c77 in main /home/you/address-sanitizer/asan/use-after-free.c:5
   ...
% ./a.out 2>&1  | ../scripts/asan_symbolize.py /you/
   ...
   #0 0x402c77 in main address-sanitizer/asan/use-after-free.c:5
   ...

To demangle functions names either add -d to asan_symbolize.py or use c++filt.

You may want to introduce your own format of the stack traces using stack_trace_format runtime flag. For example:

% ./a.out
    ...
    #0 0x4b615d in main /home/you/use-after-free.cc:12:3
    ...
% ASAN_OPTIONS='stack_trace_format="[frame=%n, function=%f, location=%S]"' ./a.out
    ...
    [frame=0, function=main, location=/home/you/use-after-free.cc:12:3]
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