[Ada] Crash on aspect/pragma Linked_Section with -gnatR2

This patch modifies the output of the representation information related to
aspect or pragma Linker_Section, achieved with compiler switch -gnatR2. The
value of the section argument is now properly retrieved. Previously it was
assumed that the value is always a N_String_Literal, however the semantics
of the annotation allow for any static string expression, including a
reference to a static string.

------------
-- Source --
------------

--  linker_sections.ads

package Linker_Sections is
   LS_1 : constant String := "1";
   LS_2 : constant String := "2" & "2";
   LS_3 : constant String := LS_1 & "3";
   LS_4 : constant String := "4" & LS_2;

   Val_1  : Integer with Linker_Section => LS_1;
   Val_2  : Integer with Linker_Section => LS_2;
   Val_3  : Integer with Linker_Section => LS_3;
   Val_4  : Integer with Linker_Section => LS_4;
   Val_5  : Integer with Linker_Section => LS_1 & "5";
   Val_6  : Integer with Linker_Section => LS_2 & "6";
   Val_7  : Integer with Linker_Section => LS_3 & "7";
   Val_8  : Integer with Linker_Section => LS_4 & "8";
   Val_9  : Integer with Linker_Section => "9"  & LS_1;
   Val_10 : Integer with Linker_Section => "10" & LS_2;
   Val_11 : Integer with Linker_Section => "11" & LS_3;
   Val_12 : Integer with Linker_Section => "12" & LS_4;

   Val_13 : Integer; pragma Linker_Section (Val_13, LS_1);
   Val_14 : Integer; pragma Linker_Section (Val_14, LS_2);
   Val_15 : Integer; pragma Linker_Section (Val_15, LS_3);
   Val_16 : Integer; pragma Linker_Section (Val_16, LS_4);
   Val_17 : Integer; pragma Linker_Section (Val_17, LS_1 & "5");
   Val_18 : Integer; pragma Linker_Section (Val_18, LS_2 & "6");
   Val_19 : Integer; pragma Linker_Section (Val_19, LS_3 & "7");
   Val_20 : Integer; pragma Linker_Section (Val_20, LS_4 & "8");
   Val_21 : Integer; pragma Linker_Section (Val_21, "9"  & LS_1);
   Val_22 : Integer; pragma Linker_Section (Val_22, "10" & LS_2);
   Val_23 : Integer; pragma Linker_Section (Val_23, "11" & LS_3);
   Val_24 : Integer; pragma Linker_Section (Val_24, "12" & LS_4);
end Linker_Sections;

-----------------
-- Compilation --
-----------------

$ gcc -c -gnatR2s linker_sections.ads

2018-05-28  Hristian Kirtchev  <kirtchev@adacore.com>

gcc/ada/

	* repinfo.adb (Expr_Value_S): New routine.
	(List_Linker_Section): Properly extract the value of the section
	argument.

From-SVN: r260825

2 files changed, 40 insertions, 10 deletions

diff --git a/gcc/ada/ChangeLog b/gcc/ada/ChangeLog
index 8e4982a..7a0a60d 100644
--- a/gcc/ada/ChangeLog
+++ b/gcc/ada/ChangeLog
@@ -1,3 +1,9 @@
+2018-05-28  Hristian Kirtchev  <kirtchev@adacore.com>
+
+	* repinfo.adb (Expr_Value_S): New routine.
+	(List_Linker_Section): Properly extract the value of the section
+	argument.
+
 2018-05-28  Patrick Bernardi  <bernardi@adacore.com>
 
 	* doc/gnat_ugn/building_executable_programs_with_gnat.rst: Update the
diff --git a/gcc/ada/repinfo.adb b/gcc/ada/repinfo.adb
index 38b2334..1fa3f4e 100644
--- a/gcc/ada/repinfo.adb
+++ b/gcc/ada/repinfo.adb
@@ -685,23 +685,47 @@ package body Repinfo is
    -------------------------
 
    procedure List_Linker_Section (Ent : Entity_Id) is
-      Arg : Node_Id;
+      function Expr_Value_S (N : Node_Id) return Node_Id;
+      --  Returns the folded value of the expression. This function is called
+      --  in instances where it has already been determined that the expression
+      --  is static or its value is known at compile time. This version is used
+      --  for string types and returns the corresponding N_String_Literal node.
+      --  NOTE: This is an exact copy of Sem_Eval.Expr_Value_S. Licensing stops
+      --  Repinfo from within Sem_Eval. Once ASIS is removed, and the licenses
+      --  are modified, Repinfo should be able to rely on Sem_Eval.
+
+      ------------------
+      -- Expr_Value_S --
+      ------------------
+
+      function Expr_Value_S (N : Node_Id) return Node_Id is
+      begin
+         if Nkind (N) = N_String_Literal then
+            return N;
+         else
+            pragma Assert (Ekind (Entity (N)) = E_Constant);
+            return Expr_Value_S (Constant_Value (Entity (N)));
+         end if;
+      end Expr_Value_S;
+
+      --  Local variables
+
+      Args : List_Id;
+      Sect : Node_Id;
+
+   --  Start of processing for List_Linker_Section
 
    begin
       if Present (Linker_Section_Pragma (Ent)) then
+         Args := Pragma_Argument_Associations (Linker_Section_Pragma (Ent));
+         Sect := Expr_Value_S (Get_Pragma_Arg (Last (Args)));
+
          Write_Str ("pragma Linker_Section (");
          List_Name (Ent);
          Write_Str (", """);
 
-         Arg :=
-           Last (Pragma_Argument_Associations (Linker_Section_Pragma (Ent)));
-
-         if Nkind (Arg) = N_Pragma_Argument_Association then
-            Arg := Expression (Arg);
-         end if;
-
-         pragma Assert (Nkind (Arg) = N_String_Literal);
-         String_To_Name_Buffer (Strval (Arg));
+         pragma Assert (Nkind (Sect) = N_String_Literal);
+         String_To_Name_Buffer (Strval (Sect));
          Write_Str (Name_Buffer (1 .. Name_Len));
          Write_Str (""");");
          Write_Eol;