During a recent project, I've tested combinations of different compiler flags and sanitizers to evaluate the relevance for debugging my C-code. By testing the impact of these combinations, I stumbled across a behavior that I did not understand.
Reproducer
I use a small hello-world code-example that contains a memory leak to trigger the address sanitizer (ASAN):
#include<stdlib.h>
#include<stdio.h>
int main () {
int * memleak = calloc(1, sizeof(int)); // no free -> leaked memory
printf ("A memleaked memory: %d\n", *memleak);
printf ("Hello World\n"); // Note: I found that if I comment out this function, ASAN will also report again
}
Observation
I worked with different combinations of compiler- and linker-flags and sometimes I observed that the address sanitizer reported the memleak, while on other occasions it did not report the memleak. I've eliminated all potential compiler-flags until I found a minimal set of flags that influenced ASAN to either report or ignore the memory leak:
ASAN will report the memory leak when compiled with the commands
cc -fsanitize=address -fno-omit-frame-pointer -Og -o main.c.o -c ./main.c && cc -o hello main.c.o -fsanitize=address,undefined && ./hello # returns 1
cc -fsanitize=address,undefined -Og -o main.c.o -c ./main.c && cc -o hello main.c.o -fsanitize=address,undefined && ./hello # returns 1
cc -fsanitize=address,undefined -fno-omit-frame-pointer -o main.c.o -c ./main.c && cc -o hello main.c.o -fsanitize=address,undefined && ./hello # returns 1
ASAN will not report the memory leak when compiled with the command
cc -fsanitize=address,undefined -fno-omit-frame-pointer -Og -o main.c.o -c ./main.c && cc -o hello main.c.o -fsanitize=address,undefined && ./hello # returns 0
However
I observe the same behavior, independent of using GCC or clang. Therefore, I'm concerned that this is not a bug, caused by an unintended interference between the different sanitizers, optimization level and the flag -fno-omit-frame-pointer, but instead it is intended behavior that I just am not able to understand, because of my lack of knowledge what the impact of -fno-omit-frame-pointer is.
If anybody could summarize what -fno-omit-frame-pointer/-fomit-frame-pointer does and in which cases it works, or explain the impact of this flag on the given example, or point me to the place where to find this information, I would be grateful.
For completeness
I'm working on Arch-linux and have the following versions of software running:
- gcc 11.1.0-1
- clang 13.0.0-2
- glibc 2.33-5
However, I've just tested and verified that the example and observations will also work on the docker image gcc:bullseye for linux/amd64 from docker-hub.
