# shellcheck shell=bash
# The link step of the compiler drivers.
#
# A driver links by handing clang its link line with -fuse-ld=<linker>; clang
# turns the line into the linker's arguments and starts the linker. In an
# installed toolchain (libexec/brint-tool is there) the driver makes that
# translation itself and calls the linker directly, so that a link needs no
# process started by clang. In a wasm32 guest clang cannot start one: LLVM
# spawns with posix_spawn, which the kernel refuses (linux#14).
#
# The translation is the one clang's wasm::Linker::ConstructJob makes for the
# link lines these drivers build: target wasm32-hwjs-unknown, no sysroot,
# -nostdlib. For such a line clang hands the linker
#
#   -m wasm32 [--strip-all] <-L and -u, in order> -L/lib
#   [--entry _initialize -shared] <inputs, in order> [--shared-memory] -o <out>
#
# where an input is a file, -l<name>, the pieces of -Wl,a,b, the word after
# -Xlinker, or -z <word>. Everything else on the line is a compile option the
# link job does not read. test/link-direct.sh holds this to what clang itself
# produces, line by line.
#
# A line this file does not model is not guessed at: hwjs_link_direct_args
# refuses it, and hwjs_link runs it through clang as before. What differs on
# the direct path, by intent:
#   - clang runs wasm-opt on the output when the line carries -O and a wasm-opt
#     sits beside clang or on PATH. The direct path never does.
#   - a clang that is not cross-compiling (a guest's) puts $LIBRARY_PATH in
#     front of the inputs as -L. The direct path does not read it, which is
#     what the cross clang on a build host does.
#   - a failed link returns the linker's own status, without clang's
#     "linker command failed" line.
#
# Usage:
#   source libexec/link-direct.sh
#   hwjs_link "$CLANG" "$LINKER" <the link line, without -fuse-ld>

# hwjs_link_direct_args <link line>: the linker's arguments in HWJS_LD_ARGS.
# Returns 1, with the reason in HWJS_LD_WHY, for a line it does not model.
hwjs_link_direct_args() {
  HWJS_LD_ARGS=(); HWJS_LD_WHY=""
  local search=() inputs=() out="a.out"
  local strip=0 shared=0 pthread=0 nostdlib=0 target=""
  local a piece
  local -a pieces
  while (($#)); do
    a="$1"; shift
    case "$a" in
      -o)        (($#)) || { HWJS_LD_WHY="-o without a value"; return 1; }
                 out="$1"; shift ;;
      -o?*)      out="${a#-o}" ;;
      -L|-u|-l|-z|-Xlinker)
                 (($#)) || { HWJS_LD_WHY="$a without a value"; return 1; }
                 case "$a" in
                   -L)       search+=( "-L$1" ) ;;
                   -u)       search+=( -u "$1" ) ;;
                   -l)       inputs+=( "-l$1" ) ;;
                   -z)       inputs+=( -z "$1" ) ;;
                   -Xlinker) inputs+=( "$1" ) ;;
                 esac
                 shift ;;
      -L?*)      search+=( "$a" ) ;;
      -u?*)      search+=( -u "${a#-u}" ) ;;
      -l?*)      inputs+=( "$a" ) ;;
      -Wl,*)     IFS=',' read -r -a pieces <<< "${a#-Wl,}"
                 for piece in "${pieces[@]}"; do inputs+=( "$piece" ); done ;;
      -s)        strip=1 ;;
      -shared)   shared=1 ;;
      -pthread)  pthread=1 ;;
      -no-pthread) pthread=0 ;;
      -nostdlib) nostdlib=1 ;;
      --target=*) target="${a#--target=}" ;;
      # Options whose link job is not the one written out above.
      -fuse-ld=*|-fprofile*|-fcoverage*|-fcs-profile*|-fsanitize*|-flto*|-fveclib*|-fopenmp*|-mexec-model=*|-mllvm)
                 HWJS_LD_WHY="'$a' changes the link job"; return 1 ;;
      # Compile options that carry their value in the next word.
      -isystem|-I|-D|-U|-include|-idirafter|-iquote|-MF|-MT|-MQ)
                 (($#)) || { HWJS_LD_WHY="$a without a value"; return 1; }
                 shift ;;
      # Compile options in one word.
      -f?*|-m?*|-O*|-g*|-W*|-D?*|-U?*|-I?*|-std=*|-stdlib=*|-nostdlibinc|-nostdinc|-nostdinc++|-nostdlib++|-nodefaultlibs|-pipe|-w|-MD|-MMD|-MP|-static|-rdynamic|-pie|-no-pie)
                 ;;
      -*|@*)     HWJS_LD_WHY="'$a' is not an option this path models"; return 1 ;;
      # Files the linker reads as they are. Any other name clang would compile
      # first, or might.
      *.o|*.a|*.so|*.so.[0-9]*|*.lo|*.obj)
                 inputs+=( "$a" ) ;;
      *)         HWJS_LD_WHY="input '$a' is not an object, an archive or a shared library by name"; return 1 ;;
    esac
  done
  [[ "$target" == wasm32-hwjs-unknown ]] || { HWJS_LD_WHY="the link target is '${target:-unset}', not wasm32-hwjs-unknown"; return 1; }
  [[ "$nostdlib" == 1 ]] || { HWJS_LD_WHY="the line has no -nostdlib, so clang would add its own startfile and libraries"; return 1; }
  HWJS_LD_ARGS=( -m wasm32 )
  [[ "$strip" == 1 ]] && HWJS_LD_ARGS+=( --strip-all )
  HWJS_LD_ARGS+=( "${search[@]}" -L/lib )
  [[ "$shared" == 1 ]] && HWJS_LD_ARGS+=( --entry _initialize -shared )
  HWJS_LD_ARGS+=( "${inputs[@]}" )
  [[ "$pthread" == 1 ]] && HWJS_LD_ARGS+=( --shared-memory )
  HWJS_LD_ARGS+=( -o "$out" )
  return 0
}

# hwjs_link <clang> <linker> <link line>: run one link and return its status.
# Reads HWJS_HOME (the toolchain root) to tell an installed toolchain from a
# source checkout. HWJS_LINK_VIA_CLANG=1 keeps an installed toolchain on the
# clang path.
hwjs_link() {
  local clang="$1" linker="$2"; shift 2
  if [[ -x "$HWJS_HOME/libexec/brint-tool" && "${HWJS_LINK_VIA_CLANG:-0}" != "1" ]]; then
    if hwjs_link_direct_args "$@"; then
      "$linker" "${HWJS_LD_ARGS[@]}"
      return $?
    fi
    echo "${0##*/}: NOTE (direct link): linking through clang instead: $HWJS_LD_WHY. In a guest clang cannot start the linker (linux#14)." >&2
  fi
  "$clang" "$@" -fuse-ld="$linker"
}