PING [PATCH v2] implement -Winfinite-recursion [PR88232]

Martin Sebor msebor@gmail.com
Fri Nov 19 15:11:12 GMT 2021


Ping:
https://gcc.gnu.org/pipermail/gcc-patches/2021-November/584205.html

On 11/11/21 2:46 PM, Martin Sebor wrote:
> Attached is a v2 of the solution I posted earlier this week
> with a few tweaks made after a more careful consideration of
> the problem and possible false negatives and positives.
> 
> 1) It avoids warning for [apparently infinitely recursive] calls
>     in noreturn functions where the recursion may be prevented by
>     a call to a noreturn function.
> 2) It avoids warning for calls where the recursion may be prevented
>     by a call to a longjmp or siglongjmp.
> 3) It warns for recursive calls to built-ins in definitions of
>     the corresponding library functions (e.g., for a call to
>     __builtin_malloc in malloc).
> 4) It warns for calls to C++ functions even if they call other
>     functions that might throw and so break out of the infinite
>     recursion.  (E.g., operator new.)  This is the same as Clang.
> 5) It doesn't warn for calls to C++ functions with the throw
>     expression.
> 
> Besides these changes to the warning itself, I've also improved
> the code a bit by making the workhorse function a member of
> the pass so recursive calls don't need to pass as many arguments
> to itself.
> 
> Retested on x86_64-linux and by building Glibc and Binutils/GDB.
> 
> A possible enhancement is to warn for calls to calloc, malloc,
> or realloc from within the definition of one of the other two
> functions.  That might be a mistake made in code that tries
> naively to replace the allocator with its own implementation.
> 
> On 11/9/21 9:28 PM, Martin Sebor wrote:
>> The attached patch adds support to the middle end for detecting
>> infinitely recursive calls.  The warning is controlled by the new
>> -Winfinite-recursion option.  The option name is the same as
>> Clang's.
>>
>> I scheduled the warning pass to run after early inlining to
>> detect mutually recursive calls but before tail recursion which
>> turns some recursive calls into infinite loops and so makes
>> the two indistinguishable.
>>
>> The warning detects a superset of problems detected by Clang
>> (based on its tests).  It detects the problem in PR88232
>> (the feature request) as well as the one in PR 87742,
>> an unrelated problem report that was root-caused to bug due
>> to infinite recursion.
>>
>> This initial version doesn't attempt to deal with superimposed
>> symbols, so those might trigger false positives.  I'm not sure
>> that's something to worry about.
>>
>> The tests are very light, but those for the exceptional cases
>> are exceedingly superficial, so it's possible those might harbor
>> some false positives and negatives.
>>
>> Tested on x86_64-linux.
>>
>> Martin
>>
> 



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