Tamas K LengyelOct 18, 2024

What do you think happens when you compile this program with clang like this & run it?

// clang -O2 -o yikes yikes.c

#include <stdio.h>

int main(void)
{
int *yikes = NULL;
*yikes = 1;

fprintf(stdout, "Hello world!\n");

return 0;
}

Compiler warning
0%
Hello world
25%
Segmentation fault
37.5%
Nothing
37.5%
Poll ended at .
Show threadTamas K LengyelOct 19, 2024
The solution was: Nothing! It turns out that due to the undefined behavior of the NULL-pointer dereference in the beginning of main, clang's optimizer removes main entirely and you just get a call to _fini! No compile time warning, no runtime warning. All is fine in the land of C! 😜
Show threadTamas K Lengyel
Perhaps even worse, even if you ask clang to produce a compiler warning for the undefined behavior with -Wnull-dereference you get nothing. At least gcc still does the right thing there:
Oct 19, 2024 at 11:40pmWeb