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
