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

[Dan Carpenter]

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.

regards,
dan carpenter