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.

9 files changed, 90 insertions, 42 deletions

diff --git a/aarch64/TargetPrinter.ml b/aarch64/TargetPrinter.ml
index e31abf71..a9d47bdd 100644
--- a/aarch64/TargetPrinter.ml
+++ b/aarch64/TargetPrinter.ml
@@ -226,7 +226,7 @@ module MacOS_System : SYSTEM =
       | Section_data i | Section_small_data i ->
           variable_section ~sec:".data" i
       | Section_const i  | Section_small_const i ->
-          variable_section ~sec:".section	__DATA,__CONST" i
+          variable_section ~sec:".const" ~reloc:".const_data" i
       | Section_string -> ".const"
       | Section_literal -> ".const"
       | Section_jumptable -> ".text"
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
diff --git a/cfrontend/C2C.ml b/cfrontend/C2C.ml
index 186c3155..fee3d86e 100644
--- a/cfrontend/C2C.ml
+++ b/cfrontend/C2C.ml
@@ -1333,8 +1333,13 @@ let convertGlobvar loc env (sto, id, ty, optinit) =
         if sto = C.Storage_extern then [] else [AST.Init_space sz]
     | Some i ->
         convertInitializer env ty i in
+  let initialized =
+    if optinit = None then Sections.Uninit else
+    if List.exists (function AST.Init_addrof _ -> true | _ -> false) init'
+    then Sections.Init_reloc
+    else Sections.Init in
   let (section, access) =
-    Sections.for_variable env loc id' ty (optinit <> None) in
+    Sections.for_variable env loc id' ty initialized in
   if Z.gt sz (Z.of_uint64 0xFFFF_FFFFL) then
     error "'%s' is too big (%s bytes)"
                    id.name (Z.to_string sz);
diff --git a/common/Sections.ml b/common/Sections.ml
index 839128a5..9858f957 100644
--- a/common/Sections.ml
+++ b/common/Sections.ml
@@ -15,12 +15,17 @@
 
 (* Handling of linker sections *)
 
+type initialized =
+  | Uninit       (* uninitialized data area *)
+  | Init         (* initialized with fixed, non-relocatable data *)
+  | Init_reloc   (* initialized with relocatable data (symbol addresses) *)
+
 type section_name =
   | Section_text
-  | Section_data of bool          (* true = init data, false = uninit data *)
-  | Section_small_data of bool
-  | Section_const of bool
-  | Section_small_const of bool
+  | Section_data of initialized
+  | Section_small_data of initialized
+  | Section_const of initialized
+  | Section_small_const of initialized
   | Section_string
   | Section_literal
   | Section_jumptable
@@ -40,6 +45,7 @@ type access_mode =
 
 type section_info = {
   sec_name_init: section_name;
+  sec_name_init_reloc: section_name;
   sec_name_uninit: section_name;
   sec_writable: bool;
   sec_executable: bool;
@@ -47,8 +53,9 @@ type section_info = {
 }
 
 let default_section_info = {
-  sec_name_init = Section_data true;
-  sec_name_uninit = Section_data false;
+  sec_name_init = Section_data Init;
+  sec_name_init_reloc = Section_data Init_reloc;
+  sec_name_uninit = Section_data Uninit;
   sec_writable = true;
   sec_executable = false;
   sec_access = Access_default
@@ -59,41 +66,49 @@ let default_section_info = {
 let builtin_sections = [
   "CODE",
      {sec_name_init = Section_text;
+      sec_name_init_reloc = Section_text;
       sec_name_uninit = Section_text;
       sec_writable = false; sec_executable = true;
       sec_access = Access_default};
   "DATA",
-     {sec_name_init = Section_data true;
-      sec_name_uninit = Section_data false;
+     {sec_name_init = Section_data Init;
+      sec_name_init_reloc = Section_data Init_reloc;
+      sec_name_uninit = Section_data Uninit;
       sec_writable = true; sec_executable = false;
       sec_access = Access_default};
   "SDATA",
-     {sec_name_init = Section_small_data true;
-      sec_name_uninit = Section_small_data false;
+     {sec_name_init = Section_small_data Init;
+      sec_name_init_reloc = Section_small_data Init_reloc;
+      sec_name_uninit = Section_small_data Uninit;
       sec_writable = true; sec_executable = false;
       sec_access = Access_near};
   "CONST",
-     {sec_name_init = Section_const true;
-      sec_name_uninit = Section_const false;
+     {sec_name_init = Section_const Init;
+      sec_name_init_reloc = Section_const Init_reloc;
+      sec_name_uninit = Section_const Uninit;
       sec_writable = false; sec_executable = false;
       sec_access = Access_default};
   "SCONST",
-     {sec_name_init = Section_small_const true;
-      sec_name_uninit = Section_small_const false;
+     {sec_name_init = Section_small_const Init;
+      sec_name_init_reloc = Section_small_const Init_reloc;
+      sec_name_uninit = Section_small_const Uninit;
       sec_writable = false; sec_executable = false;
       sec_access = Access_near};
   "STRING",
      {sec_name_init = Section_string;
+      sec_name_init_reloc = Section_string;
       sec_name_uninit = Section_string;
       sec_writable = false; sec_executable = false;
       sec_access = Access_default};
   "LITERAL",
      {sec_name_init = Section_literal;
+      sec_name_init_reloc = Section_literal;
       sec_name_uninit = Section_literal;
       sec_writable = false; sec_executable = false;
       sec_access = Access_default};
   "JUMPTABLE",
      {sec_name_init = Section_jumptable;
+      sec_name_init_reloc = Section_jumptable;
       sec_name_uninit = Section_jumptable;
       sec_writable = false; sec_executable = false;
       sec_access = Access_default}
@@ -128,15 +143,19 @@ let define_section name ?iname ?uname ?writable ?executable ?access () =
     match executable with Some b -> b | None -> si.sec_executable
   and access =
     match access with Some b -> b | None -> si.sec_access in
-  let iname =
+  let i =
     match iname with Some s -> Section_user(s, writable, executable)
                    | None -> si.sec_name_init in
-  let uname =
+  let ir =
+    match iname with Some s -> Section_user(s, writable, executable)
+                   | None -> si.sec_name_init_reloc in
+  let u =
     match uname with Some s -> Section_user(s, writable, executable)
                    | None -> si.sec_name_uninit in
   let new_si =
-    { sec_name_init = iname;
-      sec_name_uninit = uname;
+    { sec_name_init = i;
+      sec_name_init_reloc = ir;
+      sec_name_uninit = u;
       sec_writable = writable;
       sec_executable = executable;
       sec_access = access } in
@@ -156,7 +175,7 @@ let use_section_for id name =
 
 let gcc_section name readonly exec =
   let sn = Section_user(name, not readonly, exec) in
-  { sec_name_init = sn; sec_name_uninit = sn;
+  { sec_name_init = sn; sec_name_init_reloc = sn; sec_name_uninit = sn;
     sec_writable = not readonly; sec_executable = exec;
     sec_access = Access_default }
 
@@ -199,7 +218,12 @@ let for_variable env loc id ty init =
           Hashtbl.find current_section_table name
         with Not_found ->
           assert false in
-  ((if init then si.sec_name_init else si.sec_name_uninit), si.sec_access)
+  let secname =
+    match init with
+    | Uninit -> si.sec_name_uninit
+    | Init -> si.sec_name_init
+    | Init_reloc -> si.sec_name_init_reloc in
+  (secname, si.sec_access)
 
 (* Determine sections for a function definition *)
 
diff --git a/common/Sections.mli b/common/Sections.mli
index d9fd9239..a3dad3be 100644
--- a/common/Sections.mli
+++ b/common/Sections.mli
@@ -16,12 +16,17 @@
 
 (* Handling of linker sections *)
 
+type initialized =
+  | Uninit       (* uninitialized data area *)
+  | Init         (* initialized with fixed, non-relocatable data *)
+  | Init_reloc   (* initialized with relocatable data (symbol addresses) *)
+
 type section_name =
   | Section_text
-  | Section_data of bool          (* true = init data, false = uninit data *)
-  | Section_small_data of bool
-  | Section_const of bool
-  | Section_small_const of bool
+  | Section_data of initialized
+  | Section_small_data of initialized
+  | Section_const of initialized
+  | Section_small_const of initialized
   | Section_string
   | Section_literal
   | Section_jumptable
@@ -46,7 +51,7 @@ val define_section:
          -> ?writable:bool -> ?executable:bool -> ?access:access_mode -> unit -> unit
 val use_section_for: AST.ident -> string -> bool
 
-val for_variable: Env.t -> C.location -> AST.ident -> C.typ -> bool ->
+val for_variable: Env.t -> C.location -> AST.ident -> C.typ -> initialized ->
                                           section_name * access_mode
 val for_function: Env.t -> C.location -> AST.ident -> C.attributes -> section_name list
 val for_stringlit: unit -> section_name
diff --git a/powerpc/TargetPrinter.ml b/powerpc/TargetPrinter.ml
index cf00e659..e32348a3 100644
--- a/powerpc/TargetPrinter.ml
+++ b/powerpc/TargetPrinter.ml
@@ -213,7 +213,7 @@ module Diab_System : SYSTEM =
     let name_of_section = function
       | Section_text -> ".text"
       | Section_data i -> variable_section ~sec:".data" ~bss:".bss" i
-      | Section_small_data i -> if i then ".sdata" else ".sbss"
+      | Section_small_data i -> variable_section ~sec:".sdata" ~bss:".sbss" i
       | Section_const _ -> ".text"
       | Section_small_const _ -> ".sdata2"
       | Section_string -> ".text"
diff --git a/x86/TargetPrinter.ml b/x86/TargetPrinter.ml
index 102edce4..1b27ee73 100644
--- a/x86/TargetPrinter.ml
+++ b/x86/TargetPrinter.ml
@@ -194,9 +194,9 @@ module MacOS_System : SYSTEM =
       | Section_data i | Section_small_data i ->
           variable_section ~sec:".data" i
       | Section_const i  | Section_small_const i ->
-          variable_section ~sec:".const" i
+          variable_section ~sec:".const" ~reloc:".const_data" i
       | Section_string -> ".const"
-      | Section_literal -> ".literal8"
+      | Section_literal -> ".const"
       | Section_jumptable -> ".text"
       | Section_user(s, wr, ex) ->
           sprintf ".section	\"%s\", %s, %s"
@@ -914,8 +914,7 @@ module Target(System: SYSTEM):TARGET =
 
     let print_epilogue oc =
       if !need_masks then begin
-        section oc (Section_const true);
-        (* not Section_literal because not 8-bytes *)
+        section oc Section_literal;
         print_align oc 16;
         fprintf oc "%a:	.quad   0x8000000000000000, 0\n"
           raw_symbol "__negd_mask";