3 ms·
I actually encountered it a couple weeks ago. Can you spot the infinite loop in this function? char* strcpy(char* restrict d, const char* restrict s) {
by ncruces 5mo ago
I actually encountered it a couple weeks ago.
Can you spot the infinite loop in this function?
char* strcpy(char* restrict d, const char* restrict s) {
stpcpy(d, s);
return d;
}
I'll help. A call to `stpcpy` that ignores the return value can be swapped with a call to the (more likely to be optimized) `strcpy`. Since that's infinite recursion, and there is no forward progress, it's undefined behavior and anything goes.
This isn't just theory, it actually broke things in practice for me.
- rssoconnor 5mo agoNaming an externally linked function with the prefix "str" is by itself UB since that prefix is reserved for <string.h>.
- ncruces 5mo agoRight. I am doing a standard library replacement, and forgot I needed to compile freestanding. Oops. My bad. So `str` and `mem` are reserved. But then so are `to` and `is` (by <ctype.h>). Just forget about having a function named `is_valid_user`. And so are `mtx_`, `cnd_`, `thrd_`, `atomic_`, `memory_`... Which is why... everything in C is UB.