support building the aarch64 cross-compiler on macOS

.github/workflows/test.yml

@@ -44,3 +44,42 @@ jobs:
       run: MODE=muen opam exec -- dune build --root example
     - name: Compile examples with xen
       run: MODE=xen opam exec -- dune build --root example
+
+  # TEMP: end-to-end macOS check that pins the not-yet-released stack
+  # (Solo5/solo5#641 + #642, mirage/ocaml-gmp#29, ocaml/Zarith#173). solo5 is a
+  # tar pin to exercise the SOLO5_VERSION fallback. Drop once those land in opam.
+  macos-e2e:
+    name: macOS aarch64 e2e (zarith)
+    runs-on: macos-latest
+    env:
+      OPAMYES: 1
+    steps:
+    - uses: actions/checkout@v6
+    # No brew install or PATH setup: opam pulls the LLVM toolchain and target
+    # runtime through solo5-cross-aarch64's depexts, and configure resolves the
+    # keg-only tools to absolute paths.
+    - uses: ocaml/setup-ocaml@v3
+      with:
+        ocaml-compiler: 5.4.1
+        opam-pin: false
+    - name: Pin the stack and build the cross-compiler
+      run: |
+        opam pin add -n solo5 https://github.com/samoht/solo5/archive/refs/heads/macos.tar.gz
+        opam pin add -n solo5-cross-aarch64 https://github.com/samoht/solo5/archive/refs/heads/macos.tar.gz
+        opam pin add -n gmp git+https://github.com/samoht/ocaml-gmp.git#ship-gmp-pc
+        opam pin add -n zarith git+https://github.com/samoht/zarith.git#honor-ocaml-env
+        opam pin add -n ocaml-solo5-cross-aarch64 .
+        opam install ocaml-solo5-cross-aarch64
+    - name: Cross-build zarith against ocaml-gmp's pkg-config (Zarith#173)
+      run: |
+        set -euo pipefail
+        opam remove -y zarith gmp conf-gmp || true
+        opam install gmp   # ocaml-gmp fork: relocatable gmp.pc under lib/pkgconfig
+        OCAMLC="ocamlfind -toolchain solo5 ocamlc" \
+        OCAMLOPT="ocamlfind -toolchain solo5 ocamlopt" \
+        OCAMLDEP="ocamlfind -toolchain solo5 ocamldep" \
+        OCAMLMKLIB="ocamlfind -toolchain solo5 ocamlmklib" \
+        PKG_CONFIG_PATH="$(opam var lib)/pkgconfig:${PKG_CONFIG_PATH:-}" \
+        opam install zarith --verbose 2>&1 | tee zarith-build.log
+        # fail unless zarith was actually built through the solo5 cross toolchain
+        grep -qE 'aarch64-solo5-ocaml|toolchain solo5' zarith-build.log

Makefile

@@ -28,6 +28,8 @@ nolibc/libnolibc.a: phony-nolibc
 phony-nolibc:
 	$(MAKE) -C nolibc libnolibc.a \
 	    "CC=$(MAKECONF_TOOLCHAIN)-cc" \
+	    "AR=$(MAKECONF_TOOLPREFIX)ar" \
+	    "RANLIB=$(MAKECONF_TOOLPREFIX)ranlib" \
 	    "FREESTANDING_CFLAGS=$(NOLIBC_CFLAGS)"
 
 # OPENLIBM
@@ -38,6 +40,8 @@ openlibm/libopenlibm.a: phony-openlibm
 phony-openlibm:
 	$(MAKE) -C openlibm libopenlibm.a \
 	     "CC=$(MAKECONF_TOOLCHAIN)-cc" \
+	     "AR=$(MAKECONF_TOOLPREFIX)ar" \
+	     "RANLIB=$(MAKECONF_TOOLPREFIX)ranlib" \
 	     "CPPFLAGS=$(LIB_CFLAGS)"
 
 # TOOLCHAIN

configure.sh

@@ -77,6 +77,20 @@ TARGET_TRIPLET="$("$CONFIG_TARGET-cc" -dumpmachine)"
 
 MAKECONF_TOOLPREFIX="${MAKECONF_TOOLPREFIX:-$TARGET_TRIPLET-}"
 
+# On macOS the llvm- tools (ar, ranlib, nm) live in a keg-only/MacPorts bindir
+# off PATH; pin the prefix there so the build and wrappers resolve them.
+if ! command -v "${MAKECONF_TOOLPREFIX}ar" >/dev/null 2>&1; then
+    for bindir in \
+        "$(command -v brew >/dev/null 2>&1 && brew --prefix llvm 2>/dev/null)/bin" \
+        /opt/homebrew/opt/llvm/bin /usr/local/opt/llvm/bin \
+        /opt/local/libexec/llvm-*/bin; do
+        if [ -x "${bindir}/${MAKECONF_TOOLPREFIX}ar" ]; then
+            MAKECONF_TOOLPREFIX="${bindir}/${MAKECONF_TOOLPREFIX}"
+            break
+        fi
+    done
+fi
+
 case "${TARGET_TRIPLET}" in
     amd64-*|x86_64-*)
         TARGET_ARCH="x86_64"

gen_toolchain_tool.sh

@@ -100,18 +100,24 @@ gen_tool() {
       TARGET_TOOL="$TARGET_STRIP"
       ;;
   esac
+  # Resolve to an absolute path so the generated wrapper does not depend on the
+  # tool's directory being on PATH when the wrapper runs. This matters for the
+  # OTHERTOOLPREFIX tools (e.g. llvm-ar on macOS), which live outside the Solo5
+  # toolchain and the opam switch, so a plain `dune build -x` would otherwise
+  # fail to find them.
   if test "$TARGET_TOOL" ; then
     TOOL="$TARGET_TOOL"
-  elif command -v -- "$SOLO5_TOOLCHAIN-$TOOL" > /dev/null; then
-    TOOL="$SOLO5_TOOLCHAIN-$TOOL"
+  elif resolved="$(command -v -- "$SOLO5_TOOLCHAIN-$TOOL")"; then
+    TOOL="$resolved"
   else
     case "$TOOL" in
       as)
-        TOOL="$SOLO5_TOOLCHAIN-cc -c"
+        resolved="$(command -v -- "$SOLO5_TOOLCHAIN-cc")"
+        TOOL="${resolved:-$SOLO5_TOOLCHAIN-cc} -c"
         ;;
       *)
-        if command -v -- "$OTHERTOOLPREFIX$TOOL" > /dev/null; then
-          TOOL="$OTHERTOOLPREFIX$TOOL"
+        if resolved="$(command -v -- "$OTHERTOOLPREFIX$TOOL")"; then
+          TOOL="$resolved"
         fi
         ;;
     esac

nolibc/Makefile

@@ -10,7 +10,7 @@ clean:
 	$(RM) libnolibc.a *.o test-include/*.[co] test-include/sys/*.[co]
 
 CC=cc
-CFLAGS=-O2 -std=c99 -Wall -Wno-parentheses -Werror
+CFLAGS=-O2 -std=c99 -Wall -Wno-parentheses -Wno-asm-operand-widths -Werror
 CFLAGS+=$(FREESTANDING_CFLAGS)
 
 OBJS=assert.o \

ocaml-solo5-cross-aarch64.opam

@@ -13,6 +13,12 @@ build: [
    "--target=aarch64-solo5-none-static"
    "--ocaml-configure-option=--disable-flat-float-array" {ocaml-option-no-flat-float-array:installed}
    "--ocaml-configure-option=--enable-flambda" {ocaml-option-flambda:installed}
+   # macOS uses the LLVM "other" tools (llvm-ar/ranlib/nm/objcopy); the
+   # freestanding nolibc lacks the C99 float ops clang would otherwise inline,
+   # and the cross compiler is built without function sections.
+   "--othertoolprefix=llvm-" {os = "macos"}
+   "--ocaml-configure-option=--enable-imprecise-c99-float-ops" {os = "macos"}
+   "--ocaml-configure-option=--disable-function-sections" {os = "macos"}
   ]
   [make "-j%{jobs}%"]
   [make "%{name}%.install"]
@@ -31,8 +37,10 @@ depends: [
   "opatch" {build} # to patch the compiler sources
   "ocamlfind" {build}
   "ocaml-src" {build}
-  "ocaml" {= "5.4.1" | "5.5.0"}
-  "solo5" {>= "0.9.1"}
+  "ocaml" {= "5.4.1" | = "5.5.0"}
+  # On macOS the native solo5 (tenders) has no build; the cross OCaml needs
+  # only the cross toolchain + headers from solo5-cross-aarch64.
+  "solo5" {>= "0.9.1" & os != "macos"}
   "solo5-cross-aarch64" {>= "0.9.1" }
 ]
 conflicts: [
@@ -45,7 +53,8 @@ conflicts: [
 available: [
   ((os = "linux" & (arch = "x86_64" | arch = "arm64"))
   | (os = "freebsd" & arch = "x86_64")
-  | (os = "openbsd" & arch = "x86_64"))
+  | (os = "openbsd" & arch = "x86_64")
+  | (os = "macos" & arch = "arm64"))
 ]
 x-maintenance-intent: [ "(latest)" ]
 synopsis: "OCaml cross-compiler to the freestanding 64-bit ARM Solo5 backend"