[gcc r15-1528] ada: Fix bogus Address Sanitizer stack-buffer-overflow on packed record equality

[Marc Poulhi?s]

https://gcc.gnu.org/g:d69c53f73dae181c79f6ec6c7276a172476a2728

commit r15-1528-gd69c53f73dae181c79f6ec6c7276a172476a2728
Author: Eric Botcazou <ebotcazou@adacore.com>
Date:   Mon May 27 16:31:20 2024 +0200

    ada: Fix bogus Address Sanitizer stack-buffer-overflow on packed record equality
    
    We set DECL_BIT_FIELD optimistically during the translation of record types
    and clear it afterward if needed, but fail to clear other attributes in the
    latter case, which fools the logic of the Address Sanitizer.
    
    gcc/ada/
    
            * gcc-interface/utils.cc (clear_decl_bit_field): New function.
            (finish_record_type): Call clear_decl_bit_field instead of clearing
            DECL_BIT_FIELD manually.

Diff:
---
 gcc/ada/gcc-interface/utils.cc | 26 +++++++++++++++++++-------
 1 file changed, 19 insertions(+), 7 deletions(-)

diff --git a/gcc/ada/gcc-interface/utils.cc b/gcc/ada/gcc-interface/utils.cc
index 771cb1a17cad..0eb9af8d4a2d 100644
--- a/gcc/ada/gcc-interface/utils.cc
+++ b/gcc/ada/gcc-interface/utils.cc
@@ -2002,6 +2002,21 @@ finish_fat_pointer_type (tree record_type, tree field_list)
   TYPE_CONTAINS_PLACEHOLDER_INTERNAL (record_type) = 2;
 }
 
+/* Clear DECL_BIT_FIELD flag and associated markers on FIELD, which is a field
+   of aggregate type TYPE.  */
+
+static void
+clear_decl_bit_field (tree field, tree type)
+{
+  DECL_BIT_FIELD (field) = 0;
+  DECL_BIT_FIELD_TYPE (field) = NULL_TREE;
+
+  /* DECL_BIT_FIELD_REPRESENTATIVE is not defined for QUAL_UNION_TYPE since
+     it uses the same slot as DECL_QUALIFIER.  */
+  if (TREE_CODE (type) != QUAL_UNION_TYPE)
+    DECL_BIT_FIELD_REPRESENTATIVE (field) = NULL_TREE;
+}
+
 /* Given a record type RECORD_TYPE and a list of FIELD_DECL nodes FIELD_LIST,
    finish constructing the record or union type.  If REP_LEVEL is zero, this
    record has no representation clause and so will be entirely laid out here.
@@ -2112,7 +2127,7 @@ finish_record_type (tree record_type, tree field_list, int rep_level,
 	      if (TYPE_ALIGN (record_type) >= align)
 		{
 		  SET_DECL_ALIGN (field, MAX (DECL_ALIGN (field), align));
-		  DECL_BIT_FIELD (field) = 0;
+		  clear_decl_bit_field (field, record_type);
 		}
 	      else if (!had_align
 		       && rep_level == 0
@@ -2122,7 +2137,7 @@ finish_record_type (tree record_type, tree field_list, int rep_level,
 		{
 		  SET_TYPE_ALIGN (record_type, align);
 		  SET_DECL_ALIGN (field, MAX (DECL_ALIGN (field), align));
-		  DECL_BIT_FIELD (field) = 0;
+		  clear_decl_bit_field (field, record_type);
 		}
 	    }
 
@@ -2130,7 +2145,7 @@ finish_record_type (tree record_type, tree field_list, int rep_level,
 	  if (!STRICT_ALIGNMENT
 	      && DECL_BIT_FIELD (field)
 	      && value_factor_p (pos, BITS_PER_UNIT))
-	    DECL_BIT_FIELD (field) = 0;
+	    clear_decl_bit_field (field, record_type);
 	}
 
       /* Clear DECL_BIT_FIELD_TYPE for a variant part at offset 0, it's simply
@@ -2453,10 +2468,7 @@ rest_of_record_type_compilation (tree record_type)
 	     avoid generating useless attributes for the field in DWARF.  */
 	  if (DECL_SIZE (old_field) == TYPE_SIZE (field_type)
 	      && value_factor_p (pos, BITS_PER_UNIT))
-	    {
-	      DECL_BIT_FIELD (new_field) = 0;
-	      DECL_BIT_FIELD_TYPE (new_field) = NULL_TREE;
-	    }
+	    clear_decl_bit_field (new_field, new_record_type);
 	  DECL_CHAIN (new_field) = TYPE_FIELDS (new_record_type);
 	  TYPE_FIELDS (new_record_type) = new_field;