Re: [PATCH] gimple-ssa-warn-access: Fix up asan_test.C -Wdangling-pointer regression [PR104103]

[Richard Biener via Gcc-patches]

> Am 19.01.2022 um 01:04 schrieb Martin Sebor via Gcc-patches 
> <gcc-patches@gcc.gnu.org>:
> 
> On 1/18/22 16:56, Jakub Jelinek wrote:
>> Hi!
>> As reported in the PR or as I've seen since the weekend, asan_test.C fails
>> because of many warnings like:
>> /home/jakub/src/gcc/gcc/testsuite/g++.dg/asan/asan_test.cc:1157:10: error: 
>> using a dangling pointer to an unnamed temporary [-Werror=dangling-pointer=]
>> /home/jakub/src/gcc/gcc/testsuite/g++.dg/asan/asan_test.cc:1157:10: error: 
>> using a dangling pointer to an unnamed temporary [-Werror=dangling-pointer=]
>> /home/jakub/src/gcc/gcc/testsuite/g++.dg/asan/asan_test.cc:1162:27: error: 
>> using a dangling pointer to an unnamed temporary [-Werror=dangling-pointer=]
>> ...
>> (lots of them).
>> There are no dangling pointers though, the warning pass sees:
>>   some_automatic_var ={v} {CLOBBER};
>>   .ASAN_MARK (POISON, &some_automatic_var, 8);
>> and warns on that (both on user vars and on e.g. TARGET_EXPR temporaries).
>> There is nothing wrong on that, .ASAN_MARK is compiler instrumentation,
>> which doesn't even touch the variable in any way nor make it escaped.
>> What it instead does is change bytes in the shadow memory corresponding
>> to the variable to reflect that the variable is out of scope and make
>> sure that access to it would be diagnosed at runtime.
>> So, for all purposes of the -Wdangling-pointer and -Wuse-after-free
>> warnings, we should ignore this internal call.
>> Bootstrapped/regtested on x86_64-linux and i686-linux, fixes asan_test.C
>> FAIL (so no new test has been added), ok for trunk?

Ok.

Richard 

> This is in line with what's done for -Wmaybe-uninitialized so it makes
> sense to do it here as well.  -Wmaybe-uninitialized also exempts calls
> to sanitizer built-ins from checking.  I don't know if they might come
> up here but if it can't be ruled out, moving the code from
> tree-ssa-uninit.cc into a utility helper and calling it from both
> places might be a good idea.
> 
> Martin
> 
>> 2022-01-18  Jakub Jelinek  <ja...@redhat.com>
>>    PR middle-end/104103
>>    * gimple-ssa-warn-access.cc (pass_waccess::check_call): Don't check
>>    .ASAN_MARK calls.
>> --- gcc/gimple-ssa-warn-access.cc.jj    2022-01-16 20:55:46.783932110 +0100
>> +++ gcc/gimple-ssa-warn-access.cc    2022-01-18 20:56:13.697780325 +0100
>> @@ -4232,6 +4232,11 @@ pass_waccess::check_call (gcall *stmt)
>>    if (gimple_call_builtin_p (stmt, BUILT_IN_NORMAL))
>>      check_builtin (stmt);
>>  +  /* .ASAN_MARK doesn't access any vars, only modifies shadow memory.  */
>> +  if (gimple_call_internal_p (stmt)
>> +      && gimple_call_internal_fn (stmt) == IFN_ASAN_MARK)
>> +    return;
>> +
>>    if (!m_early_checks_p)
>>      if (tree callee = gimple_call_fndecl (stmt))
>>        {
>>    Jakub
>