configure

#!/bin/sh

set -e

# Configure:
# - C library: musl or glibc
# - as binary
# - ld binary
#
# The results are written to config.h

USE_MUSL=0

DEFAULT_AS_COMMAND="${AS:-$(command -v as  || true)}"   # Default assembler.
DEFAULT_LD_COMMAND="${LD:-$(command -v ld  || true)}"   # Default linker.

# Show the help
help() {
    cat <<END
Usage: ./configure [options]

Flags:
--use-musl    Use MUSL libc instead of glibc
--as=PATH     Use assembler binary (detected: $DEFAULT_AS_COMMAND)
--ld=PATH     Use linker binary    (detected: $DEFAULT_LD_COMMAND)
-h, --help    Print this help text.
END
    exit 0
}

# Parse args
for arg in "$@"; do
    case $arg in
    --use-musl)   USE_MUSL=1 ;;
    --as=*)       DEFAULT_AS_COMMAND="${arg#*=}" ;;
    --ld=*)       DEFAULT_LD_COMMAND="${arg#*=}" ;;
    -h|--help) help ;;
    *) echo "Unknown arg: $arg" >&2; exit 1 ;;
    esac
    shift || true
done

# gcc C runtime files
GCC_LIBRARY_PATH=/usr/lib/gcc/x86_64-linux-gnu/9
GCC_CRTBEGIN=/usr/lib/gcc/x86_64-linux-gnu/9/crtbeginS.o
GCC_CRTEND=/usr/lib/gcc/x86_64-linux-gnu/9/crtendS.o

# Configure libc
if [ $USE_MUSL -eq 0 ]
then
    echo Using glibc

    DYNAMIC_LINKER=/lib64/ld-linux-x86-64.so.2
    LIBC_LIBRARY_PATH=/usr/lib
    STARTFILES="/usr/lib/x86_64-linux-gnu/crt1.o /usr/lib/x86_64-linux-gnu/crti.o $GCC_CRTBEGIN"
    ENDFILES="$GCC_CRTEND /usr/lib/x86_64-linux-gnu/crtn.o"

else
    echo Using musl libc

    DYNAMIC_LINKER=/lib/ld-musl-x86_64.so.1
    LIBC_LIBRARY_PATH=/usr/lib/x86_64-linux-musl
	STARTFILES="/usr/lib/x86_64-linux-musl/Scrt1.o /usr/lib/x86_64-linux-musl/crti.o $GCC_CRTBEGIN"
	ENDFILES="$GCC_CRTEND /usr/lib/x86_64-linux-musl/crtn.o"

fi

echo Using assembler $DEFAULT_AS_COMMAND
echo Using linker $DEFAULT_LD_COMMAND

# Write out config.h
CONFIG_H_PATH=config.h

cat > $CONFIG_H_PATH <<END
// This file is auto generated. Do not edit.

#define DEFAULT_AS_COMMAND "$DEFAULT_AS_COMMAND"
#define DEFAULT_LD_COMMAND "$DEFAULT_LD_COMMAND"
#define DYNAMIC_LINKER "$DYNAMIC_LINKER"
#define LIBC_LIBRARY_PATH "$LIBC_LIBRARY_PATH"
#define GCC_LIBRARY_PATH "$GCC_LIBRARY_PATH"
#define STARTFILES "$STARTFILES"
#define ENDFILES "$ENDFILES"
END