UndefinedBehaviorSanitizer should no longer report an error about adding a NULL pointer and a 0 integer

[bhaible]

According to https://sourceware.org/pipermail/libc-alpha/2024-October/160375.html, N3322 has been accepted for inclusion in ISO C.

In particular, adding a NULL pointer and a 0 integer is no longer undefined behaviour. clang's UBSAN should therefore no longer report a "runtime error" about it.

How to reproduce:

1. Save this file as n3322-1.c:

/* This program exercises functionality allowed by
   https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3322.pdf */

#include <stddef.h>

int main ()
{
  char *volatile p1 = NULL;
  char *volatile p2 = NULL;
  ptrdiff_t n = p1 - p2;
  char *q = p1 + n;
  (void) q;
}

2. Compile it:

$ clang -fsanitize=undefined,address -O0 -fno-omit-frame-pointer -ggdb n3322-1.c

3. Run it:

$ ASAN_OPTIONS="detect_leaks=0 abort_on_error=0 allocator_may_return_null=1" ./a.out
n3322-1.c:11:16: runtime error: applying zero offset to null pointer
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior n3322-1.c:11:16 

This runtime error, seen with clang 19, should go away.

[cor3ntin]

@AaronBallman

[AaronBallman]

Note, while the proposal was for C2y, the paper was adopted as applying to older language standard modes (https://www.open-std.org/JTC1/SC22/WG14/www/previous.html).

[davidben]

I think this was fixed with #120719. (CC @nikic)

[AaronBallman]

Agreed, this is fixed: https://godbolt.org/z/n7x58fsGY