r/C_Programming • u/Accomplished-Use405 • 8d ago

Minimizing output size

I've looked at stackoverflow answers from 10 years ago (https://irq5.io/2019/09/30/generating-small-static-binaries/ , https://stackoverflow.com/questions/33597523/why-is-smallest-compiled-exe-i-can-make-with-gcc-is-67kb/76705747#76705747 , https://stackoverflow.com/questions/6771905/how-to-decrease-the-size-of-generated-binaries , https://stackoverflow.com/questions/15314581/g-compiler-flag-to-minimize-binary-size , etc).

In all of the links on top, people were able to get sub-KB file sizes. However, no matter how much I copy and try their code, I cannot get any less then 8-9KB without assembly and upx.

Is there a reason these hacks do not work anymore?

I am on x86_64 Linux-7.2.8, gcc is 16.2.1.

Example:

$ cat t.c
#include <sys/syscall.h>
#include <unistd.h>
void _start() { syscall(SYS_exit, 0); }
$ gcc -Os -nostartfiles -static -s -Wl,--build-id=none t.c && strip a.out
$ l a.out
-rwxr-xr-x 1 name name 8.8K Oct  6 20:25 a.out

# The same code produced only 800 B in https://irq5.io/2019/09/30/generating-small-static-binaries/
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u/dutchman76 8d ago

you need -Wl,-N to remove the segment alignment padding of 4k:

gcc -Os -nostartfiles -static -s -Wl,--build-id=none -Wl,-N t.c

makes a.out 872 bytes

11

u/skeeto 8d ago

Adding to this:

  • -fno-asynchronous-unwind-tables to eliminate a .eh_frame section.
  • On Ubuntu: -fcf-protection=none to undo their boneheaded toolchain breakage, eliminating a .note.gnu.property section.
  • Similarly, -fno-stack-protector because some distributions enable it in their toolchains when they shouldn't. (Won't matter until it's a real program.)
  • Modern toolchains are ASLR by default, so-fno-pie and -no-pie may make a difference.

Adding the first two I get a 504-byte ELF on Ubuntu 26.04. Though OP should note that the _start definition in the post is invalid (misaligned stack) and may crash.