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

[Dan Carpenter]

On Tue, Oct 01, 2019 at 09:58:55PM +0300, 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));

I was wrong on this.  It's built into GCC so it doesn't matter how it's
annotated.

> 
> 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.

But it's true that the kernel has -fno-delete-null-pointer-checks so I
don't think this is worth patching.

regards,
dan carpenter