[Ada] Local renaming should not be externally visible
Arnaud Charlet
charlet@adacore.com
Thu Oct 23 10:27:00 GMT 2014
This patch modifies the analysis of a package body to hide object and
subprogram renamings from external visibility.
------------
-- Source --
------------
-- externals.ads
package Externals is
procedure Force_Body;
end Externals;
-- externals.adb
package body Externals is
Obj : constant String := "Hello";
Obj_Ren : String renames Obj;
procedure Force_Body is begin null; end Force_Body;
end Externals;
-- main.adb
with Externals;
procedure Main is
begin
Externals.Force_Body;
end Main;
----------------------------
-- Compilation and output --
----------------------------
$ gnatmake -q main.adb
$ nm main | grep "externals__obj" | cut -d' ' -f2-
r externals__obj
r externals__obj_ren
Tested on x86_64-pc-linux-gnu, committed on trunk
2014-10-23 Hristian Kirtchev <kirtchev@adacore.com>
* sem_ch7.adb (Analyze_Package_Body_Helper):
The logic which hides local entities from external
visibility is now contained in routine Hide_Public_Entities.
(Hide_Public_Entities): New routine. Object and subprogram
renamings are now hidden from external visibility the same way
objects are.
-------------- next part --------------
Index: sem_ch7.adb
===================================================================
--- sem_ch7.adb (revision 216574)
+++ sem_ch7.adb (working copy)
@@ -220,12 +220,12 @@
---------------------------------
procedure Analyze_Package_Body_Helper (N : Node_Id) is
- HSS : Node_Id;
- Body_Id : Entity_Id;
- Spec_Id : Entity_Id;
- Last_Spec_Entity : Entity_Id;
- New_N : Node_Id;
- Pack_Decl : Node_Id;
+ procedure Hide_Public_Entities (Decls : List_Id);
+ -- Attempt to hide all public entities found in declarative list Decls
+ -- by resetting their Is_Public flag to False depending on whether the
+ -- entities are not referenced by inlined or generic bodies. This kind
+ -- of processing is a conservative approximation and may still leave
+ -- certain entities externally visible.
procedure Install_Composite_Operations (P : Entity_Id);
-- Composite types declared in the current scope may depend on types
@@ -233,6 +233,310 @@
-- is now in scope. Indicate that the corresponding operations on the
-- composite type are available.
+ --------------------------
+ -- Hide_Public_Entities --
+ --------------------------
+
+ procedure Hide_Public_Entities (Decls : List_Id) is
+ function Contains_Subp_Or_Const_Refs (N : Node_Id) return Boolean;
+ -- Subsidiary to routine Has_Referencer. Determine whether a node
+ -- contains a reference to a subprogram or a non-static constant.
+ -- WARNING: this is a very expensive routine as it performs a full
+ -- tree traversal.
+
+ function Has_Referencer
+ (Decls : List_Id;
+ Top_Level : Boolean := False) return Boolean;
+ -- A "referencer" is a construct which may reference a previous
+ -- declaration. Examine all declarations in list Decls in reverse
+ -- and determine whether once such referencer exists. All entities
+ -- in the range Last (Decls) .. Referencer are hidden from external
+ -- visibility.
+
+ ---------------------------------
+ -- Contains_Subp_Or_Const_Refs --
+ ---------------------------------
+
+ function Contains_Subp_Or_Const_Refs (N : Node_Id) return Boolean is
+ Reference_Seen : Boolean := False;
+
+ function Is_Subp_Or_Const_Ref
+ (N : Node_Id) return Traverse_Result;
+ -- Determine whether a node denotes a reference to a subprogram or
+ -- a non-static constant.
+
+ --------------------------
+ -- Is_Subp_Or_Const_Ref --
+ --------------------------
+
+ function Is_Subp_Or_Const_Ref
+ (N : Node_Id) return Traverse_Result
+ is
+ Val : Node_Id;
+
+ begin
+ -- Detect a reference of the form
+ -- Subp_Call
+
+ if Nkind (N) in N_Subprogram_Call
+ and then Is_Entity_Name (Name (N))
+ then
+ Reference_Seen := True;
+ return Abandon;
+
+ -- Detect a reference of the form
+ -- Subp'Some_Attribute
+
+ elsif Nkind (N) = N_Attribute_Reference
+ and then Is_Entity_Name (Prefix (N))
+ and then Is_Subprogram (Entity (Prefix (N)))
+ then
+ Reference_Seen := True;
+ return Abandon;
+
+ -- Detect the use of a non-static constant
+
+ elsif Is_Entity_Name (N)
+ and then Present (Entity (N))
+ and then Ekind (Entity (N)) = E_Constant
+ then
+ Val := Constant_Value (Entity (N));
+
+ if Present (Val)
+ and then not Compile_Time_Known_Value (Val)
+ then
+ Reference_Seen := True;
+ return Abandon;
+ end if;
+ end if;
+
+ return OK;
+ end Is_Subp_Or_Const_Ref;
+
+ procedure Find_Subp_Or_Const_Ref is
+ new Traverse_Proc (Is_Subp_Or_Const_Ref);
+
+ -- Start of processing for Contains_Subp_Or_Const_Refs
+
+ begin
+ Find_Subp_Or_Const_Ref (N);
+
+ return Reference_Seen;
+ end Contains_Subp_Or_Const_Refs;
+
+ --------------------
+ -- Has_Referencer --
+ --------------------
+
+ function Has_Referencer
+ (Decls : List_Id;
+ Top_Level : Boolean := False) return Boolean
+ is
+ Decl : Node_Id;
+ Decl_Id : Entity_Id;
+ Spec : Node_Id;
+
+ Has_Non_Subp_Const_Referencer : Boolean := False;
+ -- Flag set for inlined subprogram bodies that do not contain
+ -- references to other subprograms or non-static constants.
+
+ begin
+ if No (Decls) then
+ return False;
+ end if;
+
+ -- Examine all declarations in reverse order, hiding all entities
+ -- from external visibility until a referencer has been found. The
+ -- algorithm recurses into nested packages.
+
+ Decl := Last (Decls);
+ while Present (Decl) loop
+
+ -- A stub is always considered a referencer
+
+ if Nkind (Decl) in N_Body_Stub then
+ return True;
+
+ -- Package declaration
+
+ elsif Nkind (Decl) = N_Package_Declaration
+ and then not Has_Non_Subp_Const_Referencer
+ then
+ Spec := Specification (Decl);
+
+ -- Inspect the declarations of a non-generic package to try
+ -- and hide more entities from external visibility.
+
+ if not Is_Generic_Unit (Defining_Entity (Spec)) then
+ if Has_Referencer (Private_Declarations (Spec))
+ or else Has_Referencer (Visible_Declarations (Spec))
+ then
+ return True;
+ end if;
+ end if;
+
+ -- Package body
+
+ elsif Nkind (Decl) = N_Package_Body
+ and then Present (Corresponding_Spec (Decl))
+ then
+ Decl_Id := Corresponding_Spec (Decl);
+
+ -- A generic package body is a referencer. It would seem
+ -- that we only have to consider generics that can be
+ -- exported, i.e. where the corresponding spec is the
+ -- spec of the current package, but because of nested
+ -- instantiations, a fully private generic body may export
+ -- other private body entities. Furthermore, regardless of
+ -- whether there was a previous inlined subprogram, (an
+ -- instantiation of) the generic package may reference any
+ -- entity declared before it.
+
+ if Is_Generic_Unit (Decl_Id) then
+ return True;
+
+ -- Inspect the declarations of a non-generic package body to
+ -- try and hide more entities from external visibility.
+
+ elsif not Has_Non_Subp_Const_Referencer
+ and then Has_Referencer (Declarations (Decl))
+ then
+ return True;
+ end if;
+
+ -- Subprogram body
+
+ elsif Nkind (Decl) = N_Subprogram_Body then
+ if Present (Corresponding_Spec (Decl)) then
+ Decl_Id := Corresponding_Spec (Decl);
+
+ -- A generic subprogram body acts as a referencer
+
+ if Is_Generic_Unit (Decl_Id) then
+ return True;
+ end if;
+
+ -- An inlined subprogram body acts as a referencer
+
+ if Is_Inlined (Decl_Id)
+ or else Has_Pragma_Inline (Decl_Id)
+ then
+ -- Inspect the statements of the subprogram body
+ -- to determine whether the body references other
+ -- subprograms and/or non-static constants.
+
+ if Top_Level
+ and then not Contains_Subp_Or_Const_Refs (Decl)
+ then
+ Has_Non_Subp_Const_Referencer := True;
+ else
+ return True;
+ end if;
+ end if;
+
+ -- Otherwise this is a stand alone subprogram body
+
+ else
+ Decl_Id := Defining_Entity (Decl);
+
+ -- An inlined body acts as a referencer. Note that an
+ -- inlined subprogram remains Is_Public as gigi requires
+ -- the flag to be set.
+
+ -- Note that we test Has_Pragma_Inline here rather than
+ -- Is_Inlined. We are compiling this for a client, and
+ -- it is the client who will decide if actual inlining
+ -- should occur, so we need to assume that the procedure
+ -- could be inlined for the purpose of accessing global
+ -- entities.
+
+ if Has_Pragma_Inline (Decl_Id) then
+ if Top_Level
+ and then not Contains_Subp_Or_Const_Refs (Decl)
+ then
+ Has_Non_Subp_Const_Referencer := True;
+ else
+ return True;
+ end if;
+ else
+ Set_Is_Public (Decl_Id, False);
+ end if;
+ end if;
+
+ -- Exceptions, objects and renamings do not need to be public
+ -- if they are not followed by a construct which can reference
+ -- and export them. The Is_Public flag is reset on top level
+ -- entities only as anything nested is local to its context.
+
+ elsif Nkind_In (Decl, N_Exception_Declaration,
+ N_Object_Declaration,
+ N_Object_Renaming_Declaration,
+ N_Subprogram_Declaration,
+ N_Subprogram_Renaming_Declaration)
+ then
+ Decl_Id := Defining_Entity (Decl);
+
+ if Top_Level
+ and then not Is_Imported (Decl_Id)
+ and then not Is_Exported (Decl_Id)
+ and then No (Interface_Name (Decl_Id))
+ and then
+ (not Has_Non_Subp_Const_Referencer
+ or else Nkind (Decl) = N_Subprogram_Declaration)
+ then
+ Set_Is_Public (Decl_Id, False);
+ end if;
+ end if;
+
+ Prev (Decl);
+ end loop;
+
+ return Has_Non_Subp_Const_Referencer;
+ end Has_Referencer;
+
+ -- Local variables
+
+ Discard : Boolean := True;
+ pragma Unreferenced (Discard);
+
+ -- Start of processing for Hide_Public_Entities
+
+ begin
+ -- The algorithm examines the top level declarations of a package
+ -- body in reverse looking for a construct that may export entities
+ -- declared prior to it. If such a scenario is encountered, then all
+ -- entities in the range Last (Decls) .. construct are hidden from
+ -- external visibility. Consider:
+
+ -- package Pack is
+ -- generic
+ -- package Gen is
+ -- end Gen;
+ -- end Pack;
+
+ -- package body Pack is
+ -- External_Obj : ...; -- (1)
+
+ -- package body Gen is -- (2)
+ -- ... External_Obj ... -- (3)
+ -- end Gen;
+
+ -- Local_Obj : ...; -- (4)
+ -- end Pack;
+
+ -- In this example Local_Obj (4) must not be externally visible as
+ -- it cannot be exported by anything in Pack. The body of generic
+ -- package Gen (2) on the other hand acts as a "referencer" and may
+ -- export anything declared before it. Since the compiler does not
+ -- perform flow analysis, it is not possible to determine precisely
+ -- which entities will be exported when Gen is instantiated. In the
+ -- example above External_Obj (1) is exported at (3), but this may
+ -- not always be the case. The algorithm takes a conservative stance
+ -- and leaves entity External_Obj public.
+
+ Discard := Has_Referencer (Decls, Top_Level => True);
+ end Hide_Public_Entities;
+
----------------------------------
-- Install_Composite_Operations --
----------------------------------
@@ -256,6 +560,15 @@
end loop;
end Install_Composite_Operations;
+ -- Local variables
+
+ Body_Id : Entity_Id;
+ HSS : Node_Id;
+ Last_Spec_Entity : Entity_Id;
+ New_N : Node_Id;
+ Pack_Decl : Node_Id;
+ Spec_Id : Entity_Id;
+
-- Start of processing for Analyze_Package_Body_Helper
begin
@@ -557,272 +870,23 @@
Check_References (Spec_Id);
end if;
- -- The processing so far has made all entities of the package body
- -- public (i.e. externally visible to the linker). This is in general
- -- necessary, since inlined or generic bodies, for which code is
- -- generated in other units, may need to see these entities. The
- -- following loop runs backwards from the end of the entities of the
- -- package body making these entities invisible until we reach a
- -- referencer, i.e. a declaration that could reference a previous
- -- declaration, a generic body or an inlined body, or a stub (which may
- -- contain either of these). This is of course an approximation, but it
- -- is conservative and definitely correct.
+ -- At this point all entities of the package body are externally visible
+ -- to the linker as their Is_Public flag is set to True. This proactive
+ -- approach is necessary because an inlined or a generic body for which
+ -- code is generated in other units may need to see these entities. Cut
+ -- down the number of global symbols that do not neet public visibility
+ -- as this has two beneficial effects:
+ -- (1) It makes the compilation process more efficient.
+ -- (2) It gives the code generatormore freedom to optimize within each
+ -- unit, especially subprograms.
- -- We only do this at the outer (library) level non-generic packages.
- -- The reason is simply to cut down on the number of global symbols
- -- generated, which has a double effect: (1) to make the compilation
- -- process more efficient and (2) to give the code generator more
- -- freedom to optimize within each unit, especially subprograms.
+ -- This is done only for top level library packages or child units as
+ -- the algorithm does a top down traversal of the package body.
if (Scope (Spec_Id) = Standard_Standard or else Is_Child_Unit (Spec_Id))
and then not Is_Generic_Unit (Spec_Id)
- and then Present (Declarations (N))
then
- Make_Non_Public_Where_Possible : declare
-
- function Has_Referencer
- (L : List_Id;
- Outer : Boolean) return Boolean;
- -- Traverse given list of declarations in reverse order. Return
- -- True if a referencer is present. Return False if none is found.
- --
- -- The Outer parameter is True for the outer level call and False
- -- for inner level calls for nested packages. If Outer is True,
- -- then any entities up to the point of hitting a referencer get
- -- their Is_Public flag cleared, so that the entities will be
- -- treated as static entities in the C sense, and need not have
- -- fully qualified names. Furthermore, if the referencer is an
- -- inlined subprogram that doesn't reference other subprograms,
- -- we keep clearing the Is_Public flag on subprograms. For inner
- -- levels, we need all names to be fully qualified to deal with
- -- the same name appearing in parallel packages (right now this
- -- is tied to their being external).
-
- --------------------
- -- Has_Referencer --
- --------------------
-
- function Has_Referencer
- (L : List_Id;
- Outer : Boolean) return Boolean
- is
- Has_Referencer_Except_For_Subprograms : Boolean := False;
-
- D : Node_Id;
- E : Entity_Id;
- K : Node_Kind;
- S : Entity_Id;
-
- function Check_Subprogram_Ref (N : Node_Id)
- return Traverse_Result;
- -- Look for references to subprograms
-
- --------------------------
- -- Check_Subprogram_Ref --
- --------------------------
-
- function Check_Subprogram_Ref (N : Node_Id)
- return Traverse_Result
- is
- V : Node_Id;
-
- begin
- -- Check name of procedure or function calls
-
- if Nkind (N) in N_Subprogram_Call
- and then Is_Entity_Name (Name (N))
- then
- return Abandon;
- end if;
-
- -- Check prefix of attribute references
-
- if Nkind (N) = N_Attribute_Reference
- and then Is_Entity_Name (Prefix (N))
- and then Present (Entity (Prefix (N)))
- and then Ekind (Entity (Prefix (N))) in Subprogram_Kind
- then
- return Abandon;
- end if;
-
- -- Check value of constants
-
- if Nkind (N) = N_Identifier
- and then Present (Entity (N))
- and then Ekind (Entity (N)) = E_Constant
- then
- V := Constant_Value (Entity (N));
-
- if Present (V)
- and then not Compile_Time_Known_Value_Or_Aggr (V)
- then
- return Abandon;
- end if;
- end if;
-
- return OK;
- end Check_Subprogram_Ref;
-
- function Check_Subprogram_Refs is
- new Traverse_Func (Check_Subprogram_Ref);
-
- -- Start of processing for Has_Referencer
-
- begin
- if No (L) then
- return False;
- end if;
-
- D := Last (L);
- while Present (D) loop
- K := Nkind (D);
-
- if K in N_Body_Stub then
- return True;
-
- -- Processing for subprogram bodies
-
- elsif K = N_Subprogram_Body then
- if Acts_As_Spec (D) then
- E := Defining_Entity (D);
-
- -- An inlined body acts as a referencer. Note also
- -- that we never reset Is_Public for an inlined
- -- subprogram. Gigi requires Is_Public to be set.
-
- -- Note that we test Has_Pragma_Inline here rather
- -- than Is_Inlined. We are compiling this for a
- -- client, and it is the client who will decide if
- -- actual inlining should occur, so we need to assume
- -- that the procedure could be inlined for the purpose
- -- of accessing global entities.
-
- if Has_Pragma_Inline (E) then
- if Outer and then Check_Subprogram_Refs (D) = OK
- then
- Has_Referencer_Except_For_Subprograms := True;
- else
- return True;
- end if;
- else
- Set_Is_Public (E, False);
- end if;
-
- else
- E := Corresponding_Spec (D);
-
- if Present (E) then
-
- -- A generic subprogram body acts as a referencer
-
- if Is_Generic_Unit (E) then
- return True;
- end if;
-
- if Has_Pragma_Inline (E) or else Is_Inlined (E) then
- if Outer and then Check_Subprogram_Refs (D) = OK
- then
- Has_Referencer_Except_For_Subprograms := True;
- else
- return True;
- end if;
- end if;
- end if;
- end if;
-
- -- Processing for package bodies
-
- elsif K = N_Package_Body
- and then Present (Corresponding_Spec (D))
- then
- E := Corresponding_Spec (D);
-
- -- Generic package body is a referencer. It would seem
- -- that we only have to consider generics that can be
- -- exported, i.e. where the corresponding spec is the
- -- spec of the current package, but because of nested
- -- instantiations, a fully private generic body may
- -- export other private body entities. Furthermore,
- -- regardless of whether there was a previous inlined
- -- subprogram, (an instantiation of) the generic package
- -- may reference any entity declared before it.
-
- if Is_Generic_Unit (E) then
- return True;
-
- -- For non-generic package body, recurse into body unless
- -- this is an instance, we ignore instances since they
- -- cannot have references that affect outer entities.
-
- elsif not Is_Generic_Instance (E)
- and then not Has_Referencer_Except_For_Subprograms
- then
- if Has_Referencer
- (Declarations (D), Outer => False)
- then
- return True;
- end if;
- end if;
-
- -- Processing for package specs, recurse into declarations.
- -- Again we skip this for the case of generic instances.
-
- elsif K = N_Package_Declaration
- and then not Has_Referencer_Except_For_Subprograms
- then
- S := Specification (D);
-
- if not Is_Generic_Unit (Defining_Entity (S)) then
- if Has_Referencer
- (Private_Declarations (S), Outer => False)
- then
- return True;
- elsif Has_Referencer
- (Visible_Declarations (S), Outer => False)
- then
- return True;
- end if;
- end if;
-
- -- Objects and exceptions need not be public if we have not
- -- encountered a referencer so far. We only reset the flag
- -- for outer level entities that are not imported/exported,
- -- and which have no interface name.
-
- elsif Nkind_In (K, N_Object_Declaration,
- N_Exception_Declaration,
- N_Subprogram_Declaration)
- then
- E := Defining_Entity (D);
-
- if Outer
- and then (not Has_Referencer_Except_For_Subprograms
- or else K = N_Subprogram_Declaration)
- and then not Is_Imported (E)
- and then not Is_Exported (E)
- and then No (Interface_Name (E))
- then
- Set_Is_Public (E, False);
- end if;
- end if;
-
- Prev (D);
- end loop;
-
- return Has_Referencer_Except_For_Subprograms;
- end Has_Referencer;
-
- -- Start of processing for Make_Non_Public_Where_Possible
-
- begin
- declare
- Discard : Boolean;
- pragma Warnings (Off, Discard);
-
- begin
- Discard := Has_Referencer (Declarations (N), Outer => True);
- end;
- end Make_Non_Public_Where_Possible;
+ Hide_Public_Entities (Declarations (N));
end if;
-- If expander is not active, then here is where we turn off the
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