One useful set of gcc flags to consider when building a statically-linkable library/executable and aiming to reduce executable size is -Os -ffunction-sections -

One useful set of gcc flags to consider when building a statically-linkable library/executable and aiming to reduce executable size is -Os -ffunction-sections -fdata-sections -Wl,-gc-sections. This causes gcc to put each function in a separate section in the resulting object file, and the -gc-sections option makes ld strip the sections that are not reachable by calls from main (basically a tree-shaker).