[llvm-dev] Why leaked memory is not shown with -fsanitize=address set on macOS?

[Vitaly Buka via llvm-dev]

In this trivial example leak check happens soon after return from main().
So even if malloc was called, the pointer may still survive somewhere in
uninitialized bytes of the active stack.

I suspect at least one of leaks will be detected in this case:
int main(int argc, char *argv[]) {
        void *p = malloc(100);
        printf("%p\n", p);
        p = malloc(100);
        printf("%p\n", p);
        return 0;
}



On Wed, 12 May 2021 at 11:58, Sterling Augustine via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> I'm not set up to test lsan on macos, but I would guess that clang is
> somehow not actually generating the call to malloc. Don't know how that
> would happen, exactly.
>
> Does the call to malloc actually occur?
>
>
> On Tue, May 11, 2021 at 2:15 PM Peng Yu via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> See below. I don't see a memory leak error on macOS for the following
>> program.
>>
>> What on macOS that is different from Linux makes the compiled program
>> behaves differently?
>>
>> $ cat main.c
>> #include <stdlib.h>
>> #include <stdio.h>
>>
>> int main(int argc, char *argv[]) {
>>         void *p = malloc(100);
>>         printf("%p\n", p);
>>         return 0;
>> }
>> $ clang --version
>> Debian clang version 11.0.1-2
>> Target: x86_64-pc-linux-gnu
>> Thread model: posix
>> InstalledDir: /usr/bin
>> $ clang -fsanitize=address main.c
>> $ ./a.out
>> 0x60b0000000f0
>>
>> =================================================================
>> ==132039==ERROR: LeakSanitizer: detected memory leaks
>>
>> Direct leak of 100 byte(s) in 1 object(s) allocated from:
>>     #0 0x49832d in malloc (/tmp/a.out+0x49832d)
>>     #1 0x4c7f6f in main (/tmp/a.out+0x4c7f6f)
>>     #2 0x7fb6966a7d09 in __libc_start_main csu/../csu/libc-start.c:308:16
>>
>> SUMMARY: AddressSanitizer: 100 byte(s) leaked in 1 allocation(s).
>>
>> $ clang --version
>> Apple clang version 12.0.0 (clang-1200.0.32.28)
>> Target: x86_64-apple-darwin19.6.0
>> Thread model: posix
>> InstalledDir:
>> /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
>> $ ./a.out
>> 0x60b000000040
>>
>> --
>> Regards,
>> Peng
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>>
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