#include <stdio.h> #include "header.h" void foo(union u *ptr, int flag) { union u local; local.i = ptr->i; printf("Calling printf to trash r0..r3\n"); /* * Clang 3.1 generates the following instructions to store flag into * local.s.x. Because str is paired with ldrh, the high half-word in r0 is * uninitialized and the corresponding positions in local.s.i will be * clobbered. * * 1a: f8bd 0004 ldrh.w r0, [sp, #4] * 1e: f005 0101 and.w r1, r5, #1 * 22: f020 0001 bic.w r0, r0, #1 * 26: 4308 orrs r0, r1 * 28: 9001 str r0, [sp, #4] */ local.s.x = flag; ptr->i = local.i; }