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