use sed in Makefile instead of patches and opatch

Makefile

@@ -91,17 +91,13 @@ $(TOOLDIR_FINAL)/$(MAKECONF_TARGET_ARCH)-solo5-ocaml-%: \
 toolchains: $(TOOLCHAIN_FOR_BUILD) $(TOOLCHAIN_FINAL)
 
 # OCAML
-# Extract sources from the ocaml-src package and apply patches if there any in
-# `patches/<OCaml version>/`
+# Extract sources from the ocaml-src package and apply our patches
 ocaml:
 # First make sure the ocaml directory doesn't exist, otherwise the cp would
 # create an ocaml-src subdirectory
 	test ! -d $@
 	cp -r "$$(ocamlfind query ocaml-src)" $@
-	VERSION="$$(head -n1 ocaml/VERSION | cut -d '.' -f 1-2)" ; \
-	if test -d "patches/$$VERSION" ; then \
-	  opatch -v -C $@ "patches/$$VERSION"/*; \
-	fi
+	./patch_ocaml.sh
 
 ocaml/Makefile.config: $(LIBS) $(TOOLCHAIN_FOR_BUILD) | ocaml
 	PATH="$$PWD/$(TOOLDIR_FOR_BUILD):$$PATH" ; \

example/startup.c

@@ -1,14 +1,36 @@
 #include <solo5.h>
 
-#define CAML_NAME_SPACE
-#include <caml/callback.h>
-
 static char *unused_argv[] = { "mirage", NULL };
 
 void _nolibc_init(uintptr_t heap_start, size_t heap_size); // defined in nolibc/sysdeps_solo5.c
 
+/* Please note that this makes some additional checks whether the modifications
+   to the OCaml runtime (see patch_ocaml.sh) were successful
+   (Max_domains_{def,max} and caml_params->max_domains are 1). This is not
+   needed for a minimal hello world. */
+#define CAML_NAME_SPACE
+#define CAML_INTERNALS //not needed for a minimal hello
+#include <caml/callback.h>
+#include <caml/startup_aux.h> //not needed for a minimal hello
+#include <caml/domain.h> //not needed for a minimal hello
+
 int solo5_app_main(const struct solo5_start_info *si) {
+    //additional check for ocaml-solo5 sanity, not needed for a minimal hello
+    if (Max_domains_def != 1) {
+      fprintf(stderr, "expected Max_domains_def to be 1, found %d\n", Max_domains_def);
+      return 1;
+    };
+    //additional check for ocaml-solo5 sanity, not needed for a minimal hello
+    if (Max_domains_max != 1) {
+      fprintf(stderr, "expected Max_domains_max to be 1, found %d\n", Max_domains_max);
+      return 1;
+    };
     _nolibc_init(si->heap_start, si->heap_size);
     caml_startup(unused_argv);
+    //additional check for ocaml-solo5 sanity, not needed for a minimal hello
+    if (caml_params->max_domains != 1) {
+      fprintf(stderr, "expected max_domains to be 1, found %d\n", caml_params->max_domains);
+      return 1;
+    };
     return 0;
 }

ocaml-solo5-cross-aarch64.opam

@@ -28,10 +28,9 @@ run-test: [
   [make "test"]
 ]
 depends: [
-  "opatch" {build} # to patch the compiler sources
   "ocamlfind" {build}
   "ocaml-src" {build}
-  "ocaml" {>= "5.5.2" & < "5.6"}
+  "ocaml" {>= "5.5" & < "5.6"}
   "solo5" {>= "0.9.1"}
   "solo5-cross-aarch64" {>= "0.9.1" }
 ]

ocaml-solo5.opam

@@ -28,10 +28,9 @@ run-test: [
   [make "test"]
 ]
 depends: [
-  "opatch" {build} # to patch the compiler sources
   "ocamlfind" {build}
   "ocaml-src" {build}
-  "ocaml" {>= "5.5.2" & < "5.6"}
+  "ocaml" {>= "5.5" & < "5.6"}
   "solo5" {>= "0.9.1"}
 ]
 conflicts: [

patch_ocaml.sh

@@ -0,0 +1,35 @@
+#!/bin/sh
+
+set -eu
+
+# Are we using GNU sed or BSD sed?
+# (`sed --version` is defined only by GNU sed, btw)
+# The intent is to set `sep` so that we can call `sed -i$sep''` to make it
+# portable
+case "$(sed --version 2>&1)" in
+  *GNU*) sep='' ;;
+  *) sep=' ' ;;
+esac
+
+# PATCH 1: Set `Max_domains_{def,max}` to 1
+#
+# Solo5 is single-core with no scheduler, so avoid the useless memory
+# waste
+#
+# We have in examples/startup.c a test whether this was successful:
+# - we check Max_domains_{def,max} as well as caml_params->max_domains to be 1
+
+sed -i$sep'' \
+  -e 's/#define Max_domains_def 128/#define Max_domains_def 1/' \
+  -e 's/#define Max_domains_max 4096/#define Max_domains_max 1/' \
+  ocaml/runtime/caml/domain.h
+
+# PATCH 2: Use the same os_type as the host
+#
+# The examples/hello.exe tests this behaviour, since OCaml will complain if
+# the host-provided "fmt" package is compiled with a differently checksummed
+# Stdlib.
+
+sed -i$sep'' \
+  -e 's/ostype="None"/ostype="$(ocamlc -config-var os_type)"/' \
+  ocaml/configure