Revise and simplify the -fstruct-return and -fstruct-passing options.

- Rename '-fstruct-return' into '-fstruct-passing', because this emulation affects both function result passing and function argument passing.  Keep '-fstruct-return' as a deprecated synonymous for '-fstruct-passing'
- Remove the ability to change the ABI for struct passing via the '-fstruct-passing=<abi>' and '-fstruct-return=<abi>' command-line flags.  This was more confusing than useful.
- Produce an error if a struct/union is passed as function argument and '-fstruct-passing' is not set.  This used to be supported, using CompCert's default ABI for passing struct arguments.  However, this default ABI does not match any of the standard ABIs of our target platforms, so it is better to reject than to silently produce ABI-incompatible code.

4 files changed, 29 insertions, 46 deletions

diff --git a/cfrontend/C2C.ml b/cfrontend/C2C.ml
index 8c7ec6d8..e4001e6b 100644
--- a/cfrontend/C2C.ml
+++ b/cfrontend/C2C.ml
@@ -466,6 +466,21 @@ let convertFkind = function
       if not !Clflags.option_flongdouble then unsupported "'long double' type";
       F64
 
+let checkFunctionType env tres targs =
+  if not !Clflags.option_fstruct_passing then begin
+    if Cutil.is_composite_type env tres then
+      unsupported "function returning a struct or union (consider adding option -fstruct-passing)";
+    begin match targs with
+    | None -> ()
+    | Some l ->
+        List.iter
+          (fun (id, ty) ->
+            if Cutil.is_composite_type env ty then
+              unsupported "function parameter of struct or union type (consider adding option -fstruct-passing)")
+          l
+    end
+  end
+    
 let rec convertTyp env t =
   match t with
   | C.TVoid a -> Tvoid
@@ -487,8 +502,7 @@ let rec convertTyp env t =
   | C.TArray(ty, Some sz, a) ->
       Tarray(convertTyp env ty, convertInt sz, convertAttr a)
   | C.TFun(tres, targs, va, a) ->
-      if Cutil.is_composite_type env tres then
-        unsupported "return type is a struct or union (consider adding option -fstruct-return)";
+      checkFunctionType env tres targs;
       Tfunction(begin match targs with
                 | None -> Tnil
                 | Some tl -> convertParams env tl
@@ -549,11 +563,6 @@ let string_of_type ty =
   Format.pp_print_flush fb ();
   Buffer.contents b
 
-let supported_return_type env ty =
-  match Cutil.unroll env ty with
-  | C.TStruct _  | C.TUnion _ -> false
-  | _ -> true
-
 let is_longlong env ty =
   match Cutil.unroll env ty with
   | C.TInt((C.ILongLong|C.IULongLong), _) -> true
@@ -826,12 +835,11 @@ let rec convertExpr env e =
                targs, convertExprList env args, tres)
 
   | C.ECall(fn, args) ->
-      if not (supported_return_type env e.etyp) then
-        unsupported ("function returning a result of type " ^ string_of_type e.etyp ^ " (consider adding option -fstruct-return)");
       begin match projFunType env fn.etyp with
       | None ->
           error "wrong type for function part of a call"
       | Some(tres, targs, va) ->
+          checkFunctionType env tres targs;
           if targs = None && not !Clflags.option_funprototyped then
             unsupported "call to unprototyped function (consider adding option -funprototyped)";
           if va && not !Clflags.option_fvararg_calls then
@@ -1039,8 +1047,7 @@ and convertSwitch env is_64 = function
 (** Function definitions *)
 
 let convertFundef loc env fd =
-  if Cutil.is_composite_type env fd.fd_ret then
-    unsupported "function returning a struct or union (consider adding option -fstruct-return)";
+  checkFunctionType env fd.fd_ret (Some fd.fd_params);
   if fd.fd_vararg && not !Clflags.option_fvararg_calls then
     unsupported "variable-argument function (consider adding option -fvararg-calls)";
   let ret =
diff --git a/cparser/StructReturn.ml b/cparser/StructReturn.ml
index 82c0a04c..4e019380 100644
--- a/cparser/StructReturn.ml
+++ b/cparser/StructReturn.ml
@@ -582,11 +582,11 @@ let program p =
   struct_passing_style :=
     if !Clflags.option_interp
     then SP_ref_callee
-    else !Clflags.option_fstruct_passing_style;
+    else Configuration.struct_passing_style;
   struct_return_style :=
     if !Clflags.option_interp
     then SR_ref
-    else !Clflags.option_fstruct_return_style;
+    else Configuration.struct_return_style;
   Transform.program
     ~decl:transf_decl
     ~fundef:transf_fundef
diff --git a/driver/Clflags.ml b/driver/Clflags.ml
index 6c2cc661..b67fd638 100644
--- a/driver/Clflags.ml
+++ b/driver/Clflags.ml
@@ -16,9 +16,7 @@ let prepro_options = ref ([]: string list)
 let linker_options = ref ([]: string list)
 let assembler_options = ref ([]: string list)
 let option_flongdouble = ref false
-let option_fstruct_return = ref false
-let option_fstruct_return_style = ref Configuration.struct_return_style
-let option_fstruct_passing_style = ref Configuration.struct_passing_style
+let option_fstruct_passing = ref false
 let option_fbitfields = ref false
 let option_fvararg_calls = ref true
 let option_funprototyped = ref true
diff --git a/driver/Driver.ml b/driver/Driver.ml
index 8d144ad5..9b0e8f13 100644
--- a/driver/Driver.ml
+++ b/driver/Driver.ml
@@ -120,7 +120,7 @@ let parse_c_file sourcename ifile =
   (* Simplification options *)
   let simplifs =
     "b" (* blocks: mandatory *)
-  ^ (if !option_fstruct_return then "s" else "")
+  ^ (if !option_fstruct_passing then "s" else "")
   ^ (if !option_fbitfields then "f" else "")
   ^ (if !option_fpacked_structs then "p" else "")
   in
@@ -425,11 +425,9 @@ Preprocessing options:
 Language support options (use -fno-<opt> to turn off -f<opt>) :
   -fbitfields    Emulate bit fields in structs [off]
   -flongdouble   Treat 'long double' as 'double' [off]
-  -fstruct-return  Emulate returning structs and unions by value [off]
-  -fstruct-return=<convention>
-                 Set the calling conventions used to return structs by value
-  -fstruct-passing=<convention>
-                 Set the calling conventions used to pass structs by value
+  -fstruct-passing  Support passing structs and unions by value as function
+                    results or function arguments [off]
+  -fstruct-return   Like -fstruct-passing (deprecated)
   -fvararg-calls Support calls to variable-argument functions [on]
   -funprototyped Support calls to old-style functions without prototypes [on]
   -fpacked-structs  Emulate packed structs [off]
@@ -502,7 +500,7 @@ let print_version_and_exit _ =
 
 let language_support_options = [
   option_fbitfields; option_flongdouble;
-  option_fstruct_return; option_fvararg_calls; option_funprototyped;
+  option_fstruct_passing; option_fvararg_calls; option_funprototyped;
   option_fpacked_structs; option_finline_asm
 ]
 
@@ -611,33 +609,13 @@ let cmdline_actions =
   Exact "-quiet", Self (fun _ -> Interp.trace := 0);
   Exact "-trace", Self (fun _ -> Interp.trace := 2);
   Exact "-random", Self (fun _ -> Interp.mode := Interp.Random);
-  Exact "-all", Self (fun _ -> Interp.mode := Interp.All);
-(* Special -f options *)
-  Exact "-fstruct-passing=ref-callee",
-    Self (fun _ -> option_fstruct_passing_style := Configuration.SP_ref_callee);
-  Exact "-fstruct-passing=ref-caller",
-    Self (fun _ -> option_fstruct_return := true;
-                   option_fstruct_passing_style := Configuration.SP_ref_caller);
-  Exact "-fstruct-passing=ints",
-    Self (fun _ -> option_fstruct_return := true;
-                   option_fstruct_passing_style := Configuration.SP_split_args);
-  Exact "-fstruct-return=ref",
-    Self (fun _ -> option_fstruct_return := true;
-                   option_fstruct_return_style := Configuration.SR_ref);
-  Exact "-fstruct-return=int1248",
-    Self (fun _ -> option_fstruct_return := true;
-                   option_fstruct_return_style := Configuration.SR_int1248);
-  Exact "-fstruct-return=int1-4",
-    Self (fun _ -> option_fstruct_return := true;
-                   option_fstruct_return_style := Configuration.SR_int1to4);
-  Exact "-fstruct-return=int1-8",
-    Self (fun _ -> option_fstruct_return := true;
-                   option_fstruct_return_style := Configuration.SR_int1to8)
+  Exact "-all", Self (fun _ -> Interp.mode := Interp.All)
   ]
 (* -f options: come in -f and -fno- variants *)
 (* Language support options *)
   @ f_opt "longdouble" option_flongdouble
-  @ f_opt "struct-return" option_fstruct_return
+  @ f_opt "struct-return" option_fstruct_passing
+  @ f_opt "struct-passing" option_fstruct_passing
   @ f_opt "bitfields" option_fbitfields
   @ f_opt "vararg-calls" option_fvararg_calls
   @ f_opt "unprototyped" option_funprototyped