Big-endian testing, reproducibly

endian-test.sh

#!/usr/bin/env nix-shell
#! nix-shell -i bash --pure
#! nix-shell -p qemu gcc "pkgsCross.mips-linux-gnu.stdenv.cc" "pkgsCross.mips-linux-gnu.stdenv.cc.libc.static" "pkgsCross.s390x.stdenv.cc" "pkgsCross.s390x.stdenv.cc.libc.static"
#! nix-shell -I nixpkgs=https://github.com/NixOS/nixpkgs/archive/ac62194c3917d5f474c1a844b6fd6da2db95077d.tar.gz

# Big-endian testing with QEMU user-mode emulation and Nix cross-compilers.
# Reproduces: https://www.hanshq.net/big-endian-qemu.html

set -euo pipefail

WORKDIR=$(mktemp -d)
trap 'rm -rf "$WORKDIR"' EXIT

cat > "$WORKDIR/endian.c" << 'EOF'
#include <stdint.h>
#include <stdio.h>

int main(void)
{
        uint32_t x = 0x12345678;
        int i;

        for (i = 0; i < sizeof(x); i++) {
                printf("mem[%d] = 0x%02x\n", i, ((char*)&x)[i]);
        }

        return 0;
}
EOF

echo "=== Native (x86_64, little-endian) ==="
gcc -Wl,--no-warn-search-mismatch "$WORKDIR/endian.c" -o "$WORKDIR/endian-native"
"$WORKDIR/endian-native"

echo ""
echo "=== MIPS (big-endian, via qemu-mips) ==="
mips-unknown-linux-gnu-cc -static "$WORKDIR/endian.c" -o "$WORKDIR/endian-mips"
qemu-mips "$WORKDIR/endian-mips"

echo ""
echo "=== s390x (big-endian, via qemu-s390x) ==="
s390x-unknown-linux-gnu-cc -static "$WORKDIR/endian.c" -o "$WORKDIR/endian-s390x"
qemu-s390x "$WORKDIR/endian-s390x"