Section handling: finer control of variable initialization

Distinguish between:
- uninitialized variables, which can go in COMM if supported
- variables initialized with fixed, numeric quantities,
  which can go in a readonly section if "const"
- variables initialized with symbol addresses which may need relocation,
  which cannot go in a readonly section even if "const",
  but can go in a special "const_data" section.

Also: on macOS, use ".const" instead of ".literal8" for literals,
as not all literals have size 8.

3 files changed, 25 insertions, 10 deletions

diff --git a/backend/JsonAST.ml b/backend/JsonAST.ml
index 8905e252..d218e567 100644
--- a/backend/JsonAST.ml
+++ b/backend/JsonAST.ml
@@ -21,14 +21,22 @@ open Sections
 let pp_storage pp static =
   pp_jstring pp (if static then "Static" else "Extern")
 
+let pp_init pp init =
+  pp_jstring pp
+    (match init with
+      | Uninit -> "Uninit"
+      | Init -> "Init"
+      | Init_reloc -> "Init_reloc")
+
 let pp_section pp sec =
   let pp_simple name =
     pp_jsingle_object pp "Section Name" pp_jstring name
   and pp_complex name init =
     pp_jobject_start pp;
     pp_jmember ~first:true pp "Section Name" pp_jstring name;
-    pp_jmember pp "Init" pp_jbool init;
+    pp_jmember pp "Init" pp_init init;
     pp_jobject_end pp in
+
   match sec with
   | Section_text -> pp_simple "Text"
   | Section_data init -> pp_complex "Data" init
diff --git a/backend/PrintAsm.ml b/backend/PrintAsm.ml
index 155f5e55..22df68ae 100644
--- a/backend/PrintAsm.ml
+++ b/backend/PrintAsm.ml
@@ -121,7 +121,7 @@ module Printer(Target:TARGET) =
           let sec =
             match C2C.atom_sections name with
             | [s] -> s
-            |  _  -> Section_data true
+            |  _  -> Section_data Init
           and align =
             match C2C.atom_alignof name with
             | Some a -> a
diff --git a/backend/PrintAsmaux.ml b/backend/PrintAsmaux.ml
index 82621010..7a692d20 100644
--- a/backend/PrintAsmaux.ml
+++ b/backend/PrintAsmaux.ml
@@ -305,14 +305,21 @@ let print_version_and_options oc comment =
   fprintf oc "\n"
 
 (** Determine the name of the section to use for a variable.
-    [i] says whether the variable is initialized (true) or not (false).
-    [sec] is the name of the section to use if initialized or if
-    no other cases apply.
-    [bss] is the name of the section to use if uninitialized and
+  - [i] is the initialization status of the variable.
+  - [sec] is the name of the section to use if initialized (with no
+    relocations) or if no other cases apply.
+  - [reloc] is the name of the section to use if initialized and
+    containing relocations.  If not provided, [sec] is used.
+  - [bss] is the name of the section to use if uninitialized and
     common declarations are not used.  If not provided, [sec] is used.
 *)
 
-let variable_section ~sec ?bss i =
-  if i then sec
-  else if !Clflags.option_fcommon then "COMM"
-  else match bss with None -> sec | Some b -> b
+let variable_section ~sec ?bss ?reloc i =
+  match i with
+  | Uninit ->
+      if !Clflags.option_fcommon
+      then "COMM"
+      else begin match bss with Some s -> s | None -> sec end
+  | Init -> sec
+  | Init_reloc ->
+      begin match reloc with Some s -> s | None -> sec end