How do I get line numbers in the debug output with clang's -fsanitize=address?

Question

I am trying to debug a memory error detected by clang with asan, but missed by valgrind. But I cannot get my clang built binary to give me any useful debugging information. I can demonstrate this with a short test program:

#include <stdlib.h>
#include <string.h>

int main(void)
{
    char *a = malloc(8);
    memset(a, 0, 9);
    free(a);
    return 0;
}

(Obviously this error will be picked up by valgrind, it's purely to show the problem with clang.)

I compile it with Clang 3.4-1ubuntu1 like so:

clang -fsanitize=address -fno-sanitize-recover -o test -O0 -g test.c

Sure enough, ./test aborts and I see some debugging info:

==3309==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60200000eff8 at pc 0x43e950 bp 0x7fff168724f0 sp 0x7fff168724e8
WRITE of size 9 at 0x60200000eff8 thread T0
    #0 0x43e94f (/home/jason/Code/astest/test+0x43e94f)
    #1 0x7faa43c47de4 (/lib/x86_64-linux-gnu/libc.so.6+0x21de4)
    #2 0x43e6ac (/home/jason/Code/astest/test+0x43e6ac)
0x60200000eff8 is located 0 bytes to the right of 8-byte region [0x60200000eff0,0x60200000eff8)
allocated by thread T0 here:
    #0 0x42cc25 (/home/jason/Code/astest/test+0x42cc25)
    #1 0x43e874 (/home/jason/Code/astest/test+0x43e874)
    #2 0x7faa43c47de4 (/lib/x86_64-linux-gnu/libc.so.6+0x21de4)

But what I really want to know are the line numbers where the error occurred, and where the memory was allocated.

How do I get this information from clang+asan?

Answer 1

If we look at the clang AddressSanitizer documentation it says:

To make AddressSanitizer symbolize its output you need to set the ASAN_SYMBOLIZER_PATH environment variable to point to the llvm-symbolizer binary (or make sure llvm-symbolizer is in your $PATH):

and shows the the following example:

ASAN_SYMBOLIZER_PATH=/usr/local/bin/llvm-symbolizer ./a.out

As the OP noted, the install location may vary, but once you know where llvm-symbolizer is located the steps are the same.