[PATCH v2 2/3] winex11.drv: avoid passing NULL to memcpy (clang)

[Matteo Bruni]

2016-07-09 8:42 GMT+02:00 Alexandre Julliard <julliard at winehq.org>:
> Kirill Smirnov <kirill.k.smirnov at gmail.com> writes:
>
>> According to the standard, memcpy() and its friends
>> should never accept NULL as argument, otherwise
>> the behavior is undefined and optimizer takes this
>> into account.
>>
>> Below in the same file (line 206) caller passes
>> NULL as lpComp argument triggering this case.
>>
>> This patch is of the same nature as the following:
>>
>> commit 5a3ad0ecf08c00fc0b7b2f24e55be27b7c3f5da0
>> Author: Kirill Smirnov <kirill.k.smirnov at gmail.com>
>> Date:   Mon May 9 18:56:14 2016 +0300
>>
>>     winhlp32: Do not pass NULL to strchr() (spotted by clang).
>
> strchr has to access the pointer so obviously it can't take NULL, but
> memcpy with a zero length shouldn't, so it's not very useful compiler
> behavior IMO. Sadly it seems the standard does allow it...

Yeah and gcc has also been exploiting that for more aggressive
optimizations for a while (see
https://gcc.gnu.org/gcc-4.9/porting_to.html).
deb274226783ab886bdb44876944e156757efe2b was probably the one
significant precedent for Wine.