On 10/26/22 01:58, Ian Abbott via tz wrote:
Also in 7.22.5 Searching and sorting utilities, paragraph 1:
[...] Pointer arguments on such a call shall still have valid values, as described in 7.1.4.
Yes, that's why portable C code can't call qsort(NULL, 0, ...). It's not just an academic point. Without the patch, 'zic /dev/null' dumps core on Fedora 36 x86-64, when tzcode is built via "make CFLAGS='$(GCC_DEBUG_FLAGS)'". That's how I discovered the need for the patch. The core dump occurred because GCC translates this: qsort(links, nlinks, sizeof *links, qsort_linkcmp); as if it were this: if (nlinks == 0) __builtin_trap(); qsort(links, nlinks, sizeof *links, qsort_linkcmp); That is, if qsort's second argument is zero, the code generated by GCC doesn't call the qsort library function. Instead, it directly executes the ud2 instruction <https://www.felixcloutier.com/x86/ud>, which raises the invalid opcode exception. Presumably this is because the GCC maintainers are in the faction that says a null pointer cannot be used to pass a size-zero object to a library function. This is likely the same faction that says "char *p = NULL; return p + 0;" has undefined behavior.