posts: add m32.md
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---
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title: "Compiling C programs using -m32 on Arch in 2023"
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description: "Compiling C programs for 32bit on Arch in 2023"
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date: 2023-06-14T12:32:52+02:00
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author: wanderer - https://git.dotya.ml/wanderer
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draft: false
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toc: true
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enableGitInfo: true
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images:
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tags:
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- archlinux
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- compilation
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- 32bit
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---
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## Intro
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> **Preliminary:** To be clear, this short post is not primarily concerned with
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> *running* the 32bit programs, instead specifically *compiling C programs for
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> 32bit (x86)*.
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Compiling a `C` program for a 32bit architecture in 2023?
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Well, one might still want to poke at reversing smaller address-space programs,
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*even in 2023*, and contrary to the popular belief, there still exist pieces of
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software not ported to 64bit and architectures in use that are 32bit. Whatever
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the motivation, the *compilation* process might not be as straight-forward on
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Arch as one would maybe expect, so this post shows how it can be done. Unless
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specified otherwise, the `x86` architecture is assumed.
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### Example program
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> Just show the example program already!
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Nothing fancy, just saying hi and printing the value of `esp`. All that is
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needed is to compile this into a 32bit binary.
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```c
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/* 32ftw.c */
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#include <stdio.h>
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int main() {
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printf("hey 32!\n");
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register int e asm("esp");
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printf("esp: 0x%08x\n", e);
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return 0;
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}
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```
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For reference, the`GCC` version used was `gcc (GCC) 13.1.1 20230429`.
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## TL;DR
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To compile a 32bit `C` program on
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[64bit-only](https://wiki.archlinux.org/title/Frequently_asked_questions#What_architectures_does_Arch_support?)
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Arch, additional packages (on top of compilers/linkers) are required. As of
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2023-06-14 these are:
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* `core/lib32-glibc`
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* `core/libr32-gcc-libs`,
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which are the GNU C library (could also use [musl libc](https://musl.libc.org/)
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but that would probably necessitate compiler wrapping as GCC seems to prefer
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the GNU versions), and the 32bit version of the GCC libraries, respectively.
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### Installing deps and calling it a day
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```sh
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~ % sudo pacman -S lib32-glibc lib32-gcc-libs
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resolving dependencies...
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looking for conflicting packages...
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Package (2) New Version Net Change
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core/lib32-gcc-libs 13.1.1-1 113.12 MiB
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core/lib32-glibc 2.37-3 18.06 MiB
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Total Installed Size: 131.18 MiB
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:: Proceed with installation? [Y/n]
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```
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## The longer version
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If you ever needed to compile some `C` sources (such as the example listed
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[here](#example-program)) on Arch into a 32 bit binary? You might have
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encountered the following:
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```sh
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~ % gcc -o 32ftw -m32 32ftw.c && ./32ftw
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In file included from /usr/include/features.h:515,
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from /usr/include/bits/libc-header-start.h:33,
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from /usr/include/stdio.h:27,
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from 32ftw.c:2:
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/usr/include/gnu/stubs.h:7:11: fatal error: gnu/stubs-32.h: No such file or directory
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7 | # include <gnu/stubs-32.h>
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| ^~~~~~~~~~~~~~~~
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compilation terminated.
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```
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Alright, a quick search and [an answer on Arch
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forums](https://bbs.archlinux.org/viewtopic.php?pid=1136063#p1136063) points to
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a (spoiler: *partial*) solution: `lib32-glibc` is needed, so let's install it
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```sh
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~ % sudo pacman -S lib32-glibc
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```
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and try again:
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```sh
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~ % gcc -o 32ftw -m32 32ftw.c && ./32ftw
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/usr/sbin/ld: skipping incompatible /usr/lib/gcc/x86_64-pc-linux-gnu/13.1.1/../../../libgcc_s.so.1 when searching for libgcc_s.so.1
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/usr/sbin/ld: skipping incompatible /usr/lib/gcc/x86_64-pc-linux-gnu/13.1.1/../../../libgcc_s.so.1 when searching for libgcc_s.so.1
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/usr/sbin/ld: skipping incompatible /usr/lib/libgcc_s.so.1 when searching for libgcc_s.so.1
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/usr/sbin/ld: cannot find libgcc_s.so.1: No such file or directory
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/usr/sbin/ld: skipping incompatible /usr/lib/gcc/x86_64-pc-linux-gnu/13.1.1/../../../libgcc_s.so.1 when searching for libgcc_s.so.1
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/usr/sbin/ld: skipping incompatible /usr/lib/libgcc_s.so.1 when searching for libgcc_s.so.1
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collect2: error: ld returned 1 exit status
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```
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> Oh no, it still refuses to work.
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As is *somewhat* hinted in the linker's error message depicted above, the
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problem can be rectified by installing the GCC libraries (the 32bit version, of
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course), which in Arch's `core` repository lives under the name
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`lib32-gcc-libs`:
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```sh
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~ % sudo pacman -S lib32-gcc-libs
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```
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Now the program can finally be compiled and run and we can see it's a 32bit
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binary.
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```sh
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~ % gcc -o 32ftw -m32 32ftw.c && ./32ftw
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hey 32!
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esp: 0xff8d27f0
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~ % file ./32ftw
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32ftw: ELF 32-bit LSB pie executable, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, BuildID[sha1]=2ff0c8dce8f64db4960aa6aef6cd9936326e990d, for GNU/Linux 4.4.0, not stripped
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~ % ldd ./32ftw
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linux-gate.so.1 (0xf7f50000)
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libc.so.6 => /usr/lib32/libc.so.6 (0xf7ce5000)
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/lib/ld-linux.so.2 => /usr/lib/ld-linux.so.2 (0xf7f52000)
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```
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## Closing words
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To sum up, compiling a `C` program for 32bit on contemporary Arch works fine
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with just a handful of dependencies. In author's opinion, this could be
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highlighted better in the Archwiki, but perhaps the target audience is so small
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that it hasn't even been considered.
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For a not-much-talking summary, check out [TL;DR's calling it a
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day](#installing-deps-and-calling-it-a-day).
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