[llvm-dev] ASAN not finding any bugs?

[Tobias Hieta via llvm-dev]

Hello Alex,

Thanks for the hint. It was actually not the -O flag that created the
problem. But it pointed me in the right direction, when I passed
-fno-experimental-new-pass-manager it started to show the error. My
guess is that the new pass manager is more aggressive in removing UB?

Thanks,
Tobias

On Mon, Feb 3, 2020 at 5:29 PM Alex Brachet-Mialot
<alexbrachetmialot at gmail.com> wrote:
>
> I haven’t looked at the code gen yet because I’m not on my computer right now but I suspect that at -Os the compiler is optimizing this away because it knows it to be undefined behavior. Try with -O0.
>
> On Mon, Feb 3, 2020 at 10:53 AM Tobias Hieta via llvm-dev <llvm-dev at lists.llvm.org> wrote:
>>
>> Hello,
>>
>> I am building sanitizers for our different platforms and trying to use
>> it in an example program, but while it seems like ASAN is running it's
>> init functions (see stdout below with ASAN_OPTIONS=verbosity=1) it
>> never catches anything in the program. This is LLVM 8.0.1 btw.
>>
>> I was using this small test case:
>>
>> int main(int argc, char** argv) {
>>   int *array = new int[100];
>>   delete [] array;
>>   return array[argc];  // BOOM
>> }
>>
>> I am compiling with:
>>
>>
>> clang++ -resource-dir <path to sanitizers> -fsanitize=address
>> -shared-libasan -fno-omit-frame-pointer -Os -g -Wl,-rpath,<path to
>> sanitizers> -o hello hello.cpp
>>
>> This is the output from setting verbosity=1 - how can I debug this issue?
>>
>> ==3401806==AddressSanitizer: libc interceptors initialized
>> || `[0x10007fff8000, 0x7fffffffffff]` || HighMem ||
>> || `[0x02008fff7000, 0x10007fff7fff]` || HighShadow ||
>> || `[0x00008fff7000, 0x02008fff6fff]` || ShadowGap ||
>> || `[0x00007fff8000, 0x00008fff6fff]` || LowShadow ||
>> || `[0x000000000000, 0x00007fff7fff]` || LowMem ||
>> MemToShadow(shadow): 0x00008fff7000 0x000091ff6dff 0x004091ff6e00 0x02008fff6fff
>> redzone=16
>> max_redzone=2048
>> quarantine_size_mb=256M
>> thread_local_quarantine_size_kb=1024K
>> malloc_context_size=30
>> SHADOW_SCALE: 3
>> SHADOW_GRANULARITY: 8
>> SHADOW_OFFSET: 0x7fff8000
>> ==3401806==Installed the sigaction for signal 11
>> ==3401806==Installed the sigaction for signal 7
>> ==3401806==Installed the sigaction for signal 8
>> ==3401806==T0: stack [0x7fff3bf5c000,0x7fff3c75c000) size 0x800000;
>> local=0x7fff3c759244
>> ==3401806==AddressSanitizer Init done
>>
>> ➜ readelf -d hello
>>
>> Dynamic section at offset 0xe18 contains 25 entries:
>> Tag Type Name/Value
>> 0x0000000000000001 (NEEDED) Shared library: [libclang_rt.asan-x86_64.so]
>> 0x0000000000000001 (NEEDED) Shared library: [libstdc++.so.6]
>> 0x0000000000000001 (NEEDED) Shared library: [libm.so.6]
>> 0x0000000000000001 (NEEDED) Shared library: [libgcc_s.so.1]
>> 0x0000000000000001 (NEEDED) Shared library: [libc.so.6]
>> 0x000000000000000c (INIT) 0x400570
>> 0x000000000000000d (FINI) 0x4007b8
>> 0x0000000000000004 (HASH) 0x400278
>> 0x0000000000000005 (STRTAB) 0x400318
>> 0x0000000000000006 (SYMTAB) 0x4002a0
>> 0x000000000000000a (STRSZ) 462 (bytes)
>> 0x000000000000000b (SYMENT) 24 (bytes)
>> 0x0000000000000015 (DEBUG) 0x0
>> 0x0000000000000003 (PLTGOT) 0x601000
>> 0x0000000000000002 (PLTRELSZ) 72 (bytes)
>> 0x0000000000000014 (PLTREL) RELA
>> 0x0000000000000017 (JMPREL) 0x400528
>> 0x0000000000000007 (RELA) 0x400510
>> 0x0000000000000008 (RELASZ) 24 (bytes)
>> 0x0000000000000009 (RELAENT) 24 (bytes)
>> 0x000000006ffffffe (VERNEED) 0x4004f0
>> 0x000000006fffffff (VERNEEDNUM) 1
>> 0x000000006ffffff0 (VERSYM) 0x4004e6
>> 0x0000000000000000 (NULL) 0x0
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