On 2016.12.20 at 03:10 -0800, H. Peter Anvin wrote: > On 12/20/16 02:00, Markus Trippelsdorf wrote: > > On 2016.12.20 at 01:30 -0800, H. Peter Anvin wrote: > >> I'd strongly prefer a non-data-dependent solution, specifically adding > >> at the top of sort_relocs(): > >> > >> if (!r->count) > >> return; > >> > >> However, by my reading of the C and POSIX standards, this is a gcc > >> error: qsort() should do nothing if the count is zero. > > > > No, it is invoking undefined behavior. > > > Notice the nonnull attribute in /usr/include/stdlib.h: > > > > 739 /* Sort NMEMB elements of BASE, of SIZE bytes each, > > 740 using COMPAR to perform the comparisons. */ > > 741 extern void qsort (void *__base, size_t __nmemb, size_t __size, > > 742 __compar_fn_t __compar) __nonnull ((1, 4)); > > > > But feel free to revert my patch and add your solution. > > Well, s/gcc/glibc/ then. > > > The qsort() function shall sort an array of nel objects, the > > initial element of which is pointed to by base
NULL does not point to any object, therefore it is UB. -- Markus
