I thought of a cute problem: what is the smallest (size) ./a.out binary I can create?
Here are some rules the program should follow:

./a.out must run successfully.
$? must deterministically be 0.
The binary must be produced by GCC only; no post-processing with objcopy, hex editors, or manual patching.

We begin with the simplest program possible:
// compiled with gcc empty.c
int main() {
    return 0;
}
This gives us a file size of 15816 bytes (from stat). Not too shabby, but we will need four of the RAM used in the Apollo guidance computer to fit our binary that does nothing.

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A step-by-step exploration of minimizing a GCC-compiled C binary on Linux, starting from 15,816 bytes and reaching 400 bytes. Each optimization step is explained: stripping symbols (-s), removing startup files (-nostartfiles), eliminating libc and dynamic linking (-nostdlib -static -no-pie), dropping the .comment section (-fno-ident), removing stack unwind tables (-fno-asynchronous-unwind-tables -fno-exceptions), stripping GNU property notes (-Wa,-mx86-used-note=no), and finally removing page-alignment padding (-Wl,--nmagic). The final binary contains only the ELF header, two program headers, 11 bytes of x86-64 instructions (a direct syscall to exit(0)), and section metadata — totaling 400 bytes.

The smallest C binary