Building a static tmux binary with musl

build.sh

#!/usr/bin/env bash

set -o errexit

MUSL_VERSION=1.2.5
LIBEVENT_VERSION=2.1.12
NCURSES_VERSION=6.5
TMUX_VERSION=3.5a

TARGETDIR=$1
if [[ "${TARGETDIR}" = "" ]]; then
	TARGETDIR="${PWD}/out"
fi
mkdir -p "${TARGETDIR}"

TASKS=$(nproc)
CC=( "${TARGETDIR}/bin/musl-gcc" -static )
_CFLAGS=( -Os -ffunction-sections -fdata-sections -no-pie)
_LDFLAGS=( "-Wl,--gc-sections" -flto )


_musl() {
	if [[ ! -e musl-${MUSL_VERSION}.tar.gz ]]; then
		curl -LO https://www.musl-libc.org/releases/musl-${MUSL_VERSION}.tar.gz
	fi
	tar zxf musl-${MUSL_VERSION}.tar.gz --skip-old-files
	pushd .
	cd musl-${MUSL_VERSION}
	CFLAGS="${_CFLAGS[*]}" LDFLAGS="${_LDFLAGS[*]}" ./configure --prefix="${TARGETDIR}" --disable-shared --enable-wrapper=gcc
	make -j $TASKS
	make install
	make clean
	popd
}

_libevent() {
	if [[ ! -e libevent-${LIBEVENT_VERSION}-stable.tar.gz ]]; then
		curl -LO https://github.com/libevent/libevent/releases/download/release-${LIBEVENT_VERSION}-stable/libevent-${LIBEVENT_VERSION}-stable.tar.gz
	fi
	tar zxf libevent-${LIBEVENT_VERSION}-stable.tar.gz --skip-old-files
	pushd .
	cd libevent-${LIBEVENT_VERSION}-stable
	_cflags=("${_CFLAGS[@]}" -flto)
	CC="${CC[*]}" CFLAGS="${_cflags[*]}" LDFLAGS="${_LDFLAGS[*]}" ./configure --prefix="${TARGETDIR}" --disable-shared --disable-openssl --disable-samples
	make -j $TASKS
	make install
	make clean
	popd
}

_ncurses() {
	if [[ ! -e ncurses-${NCURSES_VERSION}.tar.gz ]]; then
		curl -LO https://ftp.gnu.org/pub/gnu/ncurses/ncurses-${NCURSES_VERSION}.tar.gz
	fi
	tar zxvf ncurses-${NCURSES_VERSION}.tar.gz --skip-old-files
	pushd .
	cd ncurses-${NCURSES_VERSION}

	_cflags=( "${_CFLAGS[@]}" -flto )
	CC="${CC[*]}" CFLAGS="${_cflags[*]}" LDFLAGS="${_LDFLAGS[*]}" ./configure --prefix $TARGETDIR \
		--with-default-terminfo-dir=/usr/share/terminfo \
		--with-terminfo-dirs="/etc/terminfo:/lib/terminfo:/usr/share/terminfo" \
		--enable-pc-files \
		--with-pkg-config-libdir="${TARGETDIR}/lib/pkgconfig" \
		--without-ada \
		--without-debug \
		--with-termlib \
		--without-cxx \
		--without-progs \
		--without-manpages \
		--disable-db-install \
		--without-tests
	make -j $TASKS
	make install
	make clean
	popd
}

_tmux() {
	if [[ ! -e tmux-${TMUX_VERSION}.tar.gz ]]; then
		curl -LO https://github.com/tmux/tmux/releases/download/${TMUX_VERSION}/tmux-${TMUX_VERSION}.tar.gz
	fi
	tar zxf tmux-${TMUX_VERSION}.tar.gz --skip-old-files
	pushd .
	cd tmux-${TMUX_VERSION}
	_cflags=( "${_CFLAGS[@]}" -flto )
	CC="${CC[*]}" CFLAGS="${_cflags[*]}" LDFLAGS="${_LDFLAGS[*]}" PKG_CONFIG_PATH="${TARGETDIR}/lib/pkgconfig" ./configure --enable-static --prefix="${TARGETDIR}"
	make -j $TASKS
	make install
	make clean
	popd

	cp "${TARGETDIR}/bin/tmux" .
	strip --strip-all ./tmux
	if command -v upx &> /dev/null; then
		upx -k --best ./tmux
	fi
}

rm -rf "${TARGETDIR}/out"

if [[ ! -x "${TARGETDIR}/bin/musl-gcc" ]]; then
	_musl
fi

_libevent
_ncurses
_tmux

Fantastic. In order to build on older systems, with a gcc that doesn't support -no-pie, add the following patch:

diff --git a/build.sh b/build.sh
index e7f6c33..720226e 100755
--- a/build.sh
+++ b/build.sh
@@ -15,7 +15,10 @@ mkdir -p "${TARGETDIR}"

 TASKS=2
 CC=( "${TARGETDIR}/bin/musl-gcc" -static )
-_CFLAGS=( -Os -ffunction-sections -fdata-sections -no-pie)
+_CFLAGS=( -Os -ffunction-sections -fdata-sections )
+if "${REALGCC:-gcc}" -v 2>&1 | grep -q -- --enable-default-pie; then
+    _CFLAGS+=( -no-pie )
+fi
 _LDFLAGS=( "-Wl,--gc-sections" -flto )

The -no-pie flag is illegal if gcc wasn't compiled with --enable-default-pie; in this case omitting it has the same effect.

With this change, it builds perfectly on CentOS 7. (For example in a centos:7 Dockerfile, use yum install -y gcc make autoconf and run build.sh.)

Adding @meermanr's patch above, it also builds in an ubuntu:20.04 container. In theory, it should build in a standard GitHub Actions runner.

I applied some of the suggested patches and bumped the versions. Also smoke tested with gcc-11 on aarch64 and x86_64.