Re: [PATCH] staging: rtl8723bs: hal: Fix memcpy calls

[Denis Efremov <efremov@linux.com>]

On 01.10.2019 21:58, Dan Carpenter wrote:
> On Tue, Oct 01, 2019 at 06:13:21PM +0300, Denis Efremov wrote:
>> Just found an official documentation to this issue:
>> https://gcc.gnu.org/gcc-4.9/porting_to.html
>> "Null pointer checks may be optimized away more aggressively
>> ...
>> The pointers passed to memmove (and similar functions in <string.h>) must be non-null
>> even when nbytes==0, so GCC can use that information to remove the check after the
>> memmove call. Calling copy(p, NULL, 0) can therefore deference a null pointer and crash."
>>
> 
> Correct.  In glibc those functions are annotated as non-NULL.
> 
> extern void *memcpy (void *__restrict __dest, const void *__restrict __src,
>                      size_t __n) __THROW __nonnull ((1, 2));
> 
> We aren't going to do that in the kernel.  A second difference is that
> in the kernel we use -fno-delete-null-pointer-checks so it doesn't
> delete the NULL checks.
> 

Thank you for the clarification. This is really helpful.

Best regards,
Denis