Public bug reported:
When using the shared libclang_rt.asan-x86_64.so, __asan_default_options
aren't working. Consider the following example:
$ cat test_asan.c
const char *__asan_default_options() {
return "help=1";
}
int main() { return 0; }
$ clang -fsanitize=address -shared-libasan test_asan.c -o
test_asan.clang.shared.x
$
LD_PRELOAD=/usr/lib/llvm-10/lib/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.so
./test_asan.clang.shared.x
[no output]
The expected behavior would be:
$ clang -fsanitize=address -static-libsan test_asan.c -o
test_asan.clang.static.x
$ ./test_asan.clang.static.x |& head
Available flags for AddressSanitizer:
quarantine_size
- Deprecated, please use quarantine_size_mb. (Current Value: -1)
quarantine_size_mb
- Size (in Mb) of quarantine used to detect use-after-free
errors. Lower value may reduce memory usage but increase the chance of false
negatives. (Current Value: -1)
thread_local_quarantine_size_kb
- Size (in Kb) of thread local quarantine used to detect
use-after-free errors. Lower value may reduce memory usage but increase the
chance of false negatives. It is not advised to go lower than 64Kb, otherwise
frequent transfers to global quarantine might affect performance. (Current
Value: -1)
redzone
- Minimal size (in bytes) of redzones around heap objects.
Requirement: redzone >= 16, is a power of two. (Current Value: 16)
max_redzone
With GCC everything works fine:
$ gcc -fsanitize=address test_asan.c -o test_asan.gcc.shared.x
$ ldd test_asan.gcc.shared.x
linux-vdso.so.1 (0x00007ffd4938e000)
libasan.so.5 => /usr/lib/x86_64-linux-gnu/libasan.so.5
(0x00007f704ffd6000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f704fde4000)
libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f704fdde000)
librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f704fdd4000)
libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0
(0x00007f704fdb1000)
libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f704fc62000)
libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1
(0x00007f704fc45000)
/lib64/ld-linux-x86-64.so.2 (0x00007f7050a1a000)
$ ./test_asan.gcc.shared.x |& head
Available flags for AddressSanitizer:
quarantine_size
- Deprecated, please use quarantine_size_mb.
quarantine_size_mb
- Size (in Mb) of quarantine used to detect use-after-free
errors. Lower value may reduce memory usage but increase the chance of false
negatives.
thread_local_quarantine_size_kb
- Size (in Kb) of thread local quarantine used to detect
use-after-free errors. Lower value may reduce memory usage but increase the
chance of false negatives. It is not advised to go lower than 64Kb, otherwise
frequent transfers to global quarantine might affect performance.
redzone
- Minimal size (in bytes) of redzones around heap objects.
Requirement: redzone >= 16, is a power of two.
max_redzone
The reason seems to be that there is no relocation for the
__asan_default_options symbol:
$ readelf --relocs
/usr/lib/llvm-10/lib/clang/10.0.0/lib/linux/libclang_rt.asan-x86_64.so | grep
__asan_default_options
[no output]
The shared libasan.so used by GCC is fine:
$ readelf --relocs /usr/lib/x86_64-linux-gnu/libasan.so.5.0.0 | grep
__asan_default_options
000000188358 03fc00000007 R_X86_64_JUMP_SLO 00000000000365d0
__asan_default_options + 0
Note that some other symbols are not affected by this. For example,
__lsan_default_options works fine even with Clang's shared
libclang_rt.asan-x86_64.so.
** Affects: llvm-defaults (Ubuntu)
Importance: Undecided
Status: New
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https://bugs.launchpad.net/bugs/1964487
Title:
__asan_default_options not working with -shared-libasan
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