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char B[256 * sizeof(void *)]; typedef void *FILE; typedef struct globals { int c; FILE *l; } __attribute__((may_alias)) T; void add_input_file(FILE *file) { (*(T*)&B).l[0] = file; } extern void abort (void); int main() { FILE x; (*(T*)&B).l = &x; add_input_file ((void *)-1); if ((*(T*)&B).l[0] != (void *)-1) abort (); return 0; }