How to make static executable without unnecessary libraries functions?

Question

For example, we have a code:

#include <stdio.h>

int main()
{
    printf("Hello, Stack Overflow!\n");
    
    return 0;
}

And we want to get statically linked executable:

$ gcc -o main main.c -static

Everything is going well, but there is one nuance:

$ du -h main
768K    main

Isn't it too much for such simple program? Let's take a list of symbols, that used in executable:

$ nm main
00000000004010f4 T abort
00000000004aec70 B __abort_msg
0000000000444be0 t add_alias2.part.0
000000000047e240 t add_fdes
000000000040163a t add_fdes.cold
0000000000444c70 t add_module.constprop.0
0000000000463570 t add_name_to_object.isra.0
0000000000462e30 t add_path.constprop.0.isra.0
00000000004adb28 d adds.1
000000000044fb70 T __add_to_environ
0000000000474210 t add_to_global_resize
00000000004741f0 t add_to_global_resize_failure.isra.0
0000000000474080 t add_to_global_update
0000000000409f50 t adjust_wide_data
00000000004af150 V __after_morecore_hook
0000000000405bd0 t alias_compare
0000000000481358 r aliasfile.0
00000000004166d0 W aligned_alloc
00000000004af178 b aligned_heap_area
0000000000461b40 T __alloc_dir
00000000004117b0 t alloc_perturb
00000000004af9c8 b any_objects_registered
0000000000486c40 r archfname
00000000004af520 b archive_stat
00000000004af500 b archloaded
00000000004af5c8 b archmapped
0000000000413780 t arena_get2.part.0
0000000000413ea0 t arena_get_retry
000000000045f8a0 T __argz_add_sep
000000000045f8a0 W argz_add_sep
000000000045f7c0 T __argz_create_sep
000000000045f7c0 W argz_create_sep
0000000000408c30 T ___asprintf
0000000000408c30 T __asprintf
0000000000408c30 W asprintf
0000000000402cd0 T __assert_fail
0000000000402b70 T __assert_fail_base
00000000004010e0 t __assert_fail_base.cold
000000000047fca0 t base_of_encoded_value
0000000000401658 t base_of_encoded_value.cold
0000000000417e60 i bcmp
0000000000495330 r blanks
00000000004953a0 r blanks
0000000000462250 T __brk
0000000000462250 W brk
00000000004ae230 B __bss_start
00000000004609d0 T __btowc
00000000004609d0 W btowc
00000000004afa00 b buf
...

In my case nm main | wc gives 1726 lines, almost of which relate to libraries like libc. So, how we can eliminate unused code in statically linked files?

There is already a similar question, but instructions in it answers work only for functions, used in project, not for libraries functions.

I do not understand the question. Unused code has been eliminated. `There is already a similar question, but instructions in it answers work only for functions, used in project, not for libraries functions` No, it works for "libraries functions" too. — KamilCuk, Aug 04 '21 at 12:36
@KamilCuk, I tried to compile with `gcc -o main main.c -static -fdata-sections -ffunction-sections -Wl,--gc-sections`, but executable is still too large - 744 KBytes — Somebody, Aug 04 '21 at 12:39
@KamilCuk, for example, I see function `brk()` - how does it relate to the program code? — Somebody, Aug 04 '21 at 12:41
It allocates memory, `printf` (and `stdio`) needs memory allocation. Anyway, inspect assembly and find out. — KamilCuk, Aug 04 '21 at 12:41
@KamilCuk, OK, but do we need all the other functions for such simple program? I understand, that many functions are needed for bootstrapping, but are there really all functions needed?.. — Somebody, Aug 04 '21 at 12:44
@KamilCuk, you're right, there are really only the necessary functions... Incredible... — Somebody, Aug 04 '21 at 12:57
What's the size if you strip all symbol information with `-s`? — ssbssa, Aug 05 '21 at 13:01

score 2 · Accepted Answer · answered Aug 19 '21 at 15:35

So, how we can eliminate unused code in statically linked files?

GLIBC is not optimized for static linkinig. If you want small statically linked binaries, use some other libc, e.g. dietlibc. See this comparison of available options.

While it could be argued that your sample program does use printf, and therefore linking all the associated support code is justified, the same can not be said for this program:

int main() { return 0; }

And yet that program (when statically linked) weights in at 765KiB on my system using Debian GLIBC 2.31-13:

$ gcc tt.c -static
$ ls -l a.out
-rwxr-x--- 1 user user 782648 Aug 19 08:28 a.out

How to make static executable without unnecessary libraries functions?

1 Answers1