Nov 202016

Did you know that when you compile a C file and use external libraries ALL the library code gets put into your binary? Even function that you don’t use? This is the default for gcc, but there is a way to remove them:

Instead of doing
gcc h.c -o h-in-c

You would do:
gcc -s -Os -ffunction-sections -fdata-sections -fno-ident h.c -o h-in-c

Using gcc 6.2.0 a simple hello world was 8kb without optimizing and 6kb with optimizations! For dnsmasq the filesize dropped from 320kb to 282kb (and after UPX packing to 174kb)!