Add support for new DWARF overlay operationsusers/zaric/location_on_dwarf_stack

Another complex DWARF expression operations, that are usefull for
SIMD/SIMT like architectures are: DW_OP_LLVM_overlay and
DW_OP_LLVM_bit_overlay. These operations pop four stack entries,
where the first must be an integral that represents an overlay size,
the second must be an integral that represents a starting point of the
overlay from the base location, the third must be a location
description that represents the overlay location description and the
forth must be a location description that represents the base location
description.

Resulting composite location description contains parts from base
location description, overlayed by the overlay location description,
starting from the overlay offset, ending at a sum of the overlay offset
and overlay size.

A new test in gdb.dwarf2 called dw2-llvm-overlay has been also added to
test the support for both operations.

1 files changed, 78 insertions, 0 deletions

diff --git a/gdb/dwarf2/expr.c b/gdb/dwarf2/expr.c
index 66bb8dd..c9c8f3a 100644
--- a/gdb/dwarf2/expr.c
+++ b/gdb/dwarf2/expr.c
@@ -2837,6 +2837,21 @@ private:
   void create_select_composite (const loc_offset &piece_size,
 				ULONGEST pieces_count);
 
+  /* It pops two stack entries.  First must be a location description
+     that represents the overlay location description.  The Second
+     must be a location description that represents the base location
+     description.  The OVERLAY_SIZE represents the size of the overlay
+     piece of the composite and the OVERLAY_OFFSET represent a starting
+     point of the overlay from the base location.
+
+     A complete composite location description created with parts from
+     base location description, overlayed by the overlay location
+     description, starting from the overlay offset, ending at
+     a sum of the overlay offset and overlay size, is pushed
+     on top of the DWARF stack.  */
+  void create_overlay_composite (loc_offset overlay_size,
+				 loc_offset overlay_offset);
+
   /* The engine for the expression evaluator.  Using the context in this
      object, evaluate the expression between OP_PTR and OP_END.  */
   void execute_stack_op (const gdb_byte *op_ptr, const gdb_byte *op_end);
@@ -3279,6 +3294,38 @@ dwarf_expr_context::create_select_composite (const loc_offset &piece_size,
 }
 
 void
+dwarf_expr_context::create_overlay_composite (loc_offset overlay_size,
+					      loc_offset overlay_offset)
+{
+  gdbarch *arch = this->m_per_objfile->objfile->arch ();
+
+  if (stack_empty_p ())
+    ill_formed_expression ();
+
+  dwarf_location_up overlay = to_location (pop (), arch);
+
+  if (stack_empty_p ())
+    ill_formed_expression ();
+
+  dwarf_location_up base = to_location (pop (), arch);
+
+  std::unique_ptr<dwarf_composite> composite
+    = make_unique<dwarf_composite> (arch, this->m_per_cu);
+
+  composite->add_piece (std::move (base->slice (0, overlay_offset)),
+			overlay_offset);
+  composite->add_piece (std::move (overlay), overlay_size);
+
+  loc_offset end_offset = overlay_offset + overlay_size;
+  loc_offset end_size = base->size () - end_offset;
+
+  composite->add_piece
+    (std::move (base->slice (end_offset, end_size)), end_size);
+  composite->set_completed (true);
+  push (std::move (composite));
+}
+
+void
 dwarf_expr_context::eval (const gdb_byte *addr, size_t len)
 {
   int old_recursion_depth = this->m_recursion_depth;
@@ -4540,6 +4587,37 @@ dwarf_expr_context::execute_stack_op (const gdb_byte *op_ptr,
 	    break;
 	  }
 
+	case DW_OP_LLVM_overlay:
+	case DW_OP_LLVM_bit_overlay:
+	  {
+	    if (stack_empty_p ())
+	      ill_formed_expression ();
+
+	    dwarf_value_up overlay_size_val
+	      = to_value (pop (), address_type);
+	    dwarf_require_integral (overlay_size_val->type ());
+	    LONGEST overlay_size = overlay_size_val->to_long ();
+
+	    if (stack_empty_p () || overlay_size < 0)
+	      ill_formed_expression ();
+
+	    dwarf_value_up overlay_offset_val
+	       = to_value (pop (), address_type);
+	    dwarf_require_integral (overlay_offset_val->type ());
+	    LONGEST overlay_offset = overlay_offset_val->to_long ();
+
+	    if (overlay_offset < 0)
+	      ill_formed_expression ();
+
+	    if (op == DW_OP_LLVM_overlay)
+	      create_overlay_composite ({(ULONGEST) overlay_size, 0},
+					{(ULONGEST) overlay_offset, 0});
+	    else
+	      create_overlay_composite ((ULONGEST) overlay_size,
+					(ULONGEST) overlay_offset);
+	    break;
+	  }
+
 	default:
 	  error (_("Unhandled dwarf expression opcode 0x%x"), op);
 	}