https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93052
--- Comment #2 from Alexander Cherepanov <ch3root at openwall dot com> ---
Example with a dead malloc (phiopt2):
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#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
__attribute__((noipa,optnone)) // imagine it in a separate TU
static void *opaque(void *p) { return p; }
static int been_there = 0;
static uintptr_t f(uintptr_t ip, uintptr_t iq)
{
if (ip == iq) {
been_there = 1;
return ip;
} else {
been_there = 0;
return iq;
}
}
int main()
{
int *q = malloc(sizeof(int));
opaque(q);
uintptr_t iq = (uintptr_t)(void *)q;
free(q);
int *p = malloc(sizeof(int));
opaque(p);
uintptr_t ip = (uintptr_t)(void *)p;
uintptr_t ir = f(ip, iq);
if (been_there) {
*p = 1;
*(int *)(void *)ir = 2;
printf("result: %d\n", *p);
}
}
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$ gcc -std=c11 -pedantic -Wall -Wextra -Wno-attributes test.c && ./a.out
result: 2
$ gcc -std=c11 -pedantic -Wall -Wextra -Wno-attributes -O3 test.c && ./a.out
result: 1
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gcc x86-64 version: gcc (GCC) 10.0.0 20191223 (experimental)
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