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# gcc - Cross compilation

From 64bits for 32bits: gcc -m32

From 32bits for 64bits: gcc -m64

# ArchLinux

# Pre-requisites

To enable 32 bits libraries on ArchLinux, in /etc/pacman.conf uncomment:

[multilib]
Include = /etc/pacman.d/mirrorlist

Install multilib gcc:

sudo pacman -Syu gcc-multilib gcc-libs-multilib lib32-glibc lib32-libtool lib32-gcc-libs

# chroot

Building in a 32-bit clean chroot - ArchWiki

# Finding missing lib32 libs 

$ pkgfile libgcc_s.so.1
core/gcc-libs
core/lib32-gcc-libs
community/aarch64-linux-gnu-gcc
community/riscv64-linux-gnu-gcc

$ pkgfile stubs-32.h   
core/lib32-glibc
community/zig

# Troubleshooting

# What is "error while loading shared libraries: requires glibc 2.5 or later dynamic linker"?

c - gcc: Reduce libc required version - Stack Overflow

gcc -m32 -Wl,--hash-style=both

# old version of glibc 

/tmp/15285_32: /lib/tls/libc.so.6: version `GLIBC_2.4' not found (required by /tmp/15285_32)
/tmp/15285_32: /lib/tls/libc.so.6: version `GLIBC_2.7' not found (required by /tmp/15285_32)

So use an old glibc in LDPRELOAD or compile with -static, ex: gcc -m32 -Wl,--hash-style=both -static -o 15285_32 15285.c

# Find target version of glibc 

$ ldd --version
ldd (GNU libc) 2.3.4

# Find old glibc tarballs:

Index of /gnu/glibc

# OLD machines

compilation exploit