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
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