Commit f55ab6f9 authored by Adrian Prantl's avatar Adrian Prantl
Browse files

Fix a buffer-size bug when the first DW_OP_piece is undefined 

and document the shortcomings of LLDB's partially defined DW_OP_piece
handling.

This would manifest as "DW_OP_piece for offset foo but top of stack is
of size bar".

rdar://problem/46262998

Differential Revision: https://reviews.llvm.org/D72880
parent 7b0d58e3

lldb/source/Expression/DWARFExpression.cpp

+5 −1
Original line number Diff line number Diff line
@@ -2071,6 +2071,10 @@ bool DWARFExpression::Evaluate( 
          // not available. Fill with zeros for now by resizing the data and

          // appending it

          curr_piece.ResizeData(piece_byte_size);

          // Note that "0" is not a correct value for the unknown bits.

          // It would be better to also return a mask of valid bits together

          // with the expression result, so the debugger can print missing

          // members as "<optimized out>" or something.

          ::memset(curr_piece.GetBuffer().GetBytes(), 0, piece_byte_size);

          pieces.AppendDataToHostBuffer(curr_piece);

        } else {
@@ -2193,8 +2197,8 @@ bool DWARFExpression::Evaluate( 
              return false;

            }

          }

          op_piece_offset += piece_byte_size;

        }

        op_piece_offset += piece_byte_size;

      }

    } break;

lldb/unittests/Expression/DWARFExpressionTest.cpp

+5 −0
Original line number Diff line number Diff line
@@ -355,4 +355,9 @@ TEST(DWARFExpression, DW_OP_piece) { 
  EXPECT_THAT_EXPECTED(Evaluate({DW_OP_const2u, 0x11, 0x22, DW_OP_piece, 2,

                                 DW_OP_const2u, 0x33, 0x44, DW_OP_piece, 2}),

                       llvm::HasValue(GetScalar(32, 0x44332211, true)));

  EXPECT_THAT_EXPECTED(

      Evaluate({DW_OP_piece, 1, DW_OP_const1u, 0xff, DW_OP_piece, 1}),

      // Note that the "00" should really be "undef", but we can't

      // represent that yet.

      llvm::HasValue(GetScalar(16, 0xff00, true)));

}