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 _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
