[PATCH] Allow DW_OP_GNU_uninit in dwarf_expr_require_composition

Andreas Arnez
2016-04-27T17:38:50Z

In DWARF expression handling, some operators are required to be either
at the end of an expression or followed by a composition operator. So
far only the operators DW_OP_reg0-31 were allowed to be followed by
DW_OP_GNU_uninit instead, and particularly DW_OP_regx was not, which is
obviously inconsistent.

This patch allows DW_OP_GNU_uninit after all operators requiring a
composition, to simplify the code and make it more consistent. This
policy may be more permissive than necessary, but in the worst case just
leads to a DWARF location description resulting in an uninitialized
value instead of an error message.

gdb/ChangeLog:

* dwarf2expr.c (dwarf_expr_require_composition): Allow
DW_OP_GNU_uninit.
(execute_stack_op): Use dwarf_expr_require_composition instead of
copying its logic.
---
gdb/dwarf2expr.c | 17 +++++------------
1 file changed, 5 insertions(+), 12 deletions(-)

diff --git a/gdb/dwarf2expr.c b/gdb/dwarf2expr.c
index 7bf3c78..bf2107a 100644
--- a/gdb/dwarf2expr.c
+++ b/gdb/dwarf2expr.c
@@ -401,16 +401,15 @@ safe_skip_leb128 (const gdb_byte *buf, const gdb_byte *buf_end)
\f

/* Check that the current operator is either at the end of an
- expression, or that it is followed by a composition operator. */
+ expression, or that it is followed by a composition operator or by
+ DW_OP_GNU_uninit (which should terminate the expression). */

void
dwarf_expr_require_composition (const gdb_byte *op_ptr, const gdb_byte *op_end,
const char *op_name)
{
- /* It seems like DW_OP_GNU_uninit should be handled here. However,
- it doesn't seem to make sense for DW_OP_*_value, and it was not
- checked at the other place that this function is called. */
- if (op_ptr != op_end && *op_ptr != DW_OP_piece && *op_ptr != DW_OP_bit_piece)
+ if (op_ptr != op_end && *op_ptr != DW_OP_piece && *op_ptr != DW_OP_bit_piece
+ && *op_ptr != DW_OP_GNU_uninit)
error (_("DWARF-2 expression error: `%s' operations must be "
"used either alone or in conjunction with DW_OP_piece "
"or DW_OP_bit_piece."),
@@ -818,13 +817,7 @@ execute_stack_op (struct dwarf_expr_context *ctx,
case DW_OP_reg29:
case DW_OP_reg30:
case DW_OP_reg31:
- if (op_ptr != op_end
- && *op_ptr != DW_OP_piece
- && *op_ptr != DW_OP_bit_piece
- && *op_ptr != DW_OP_GNU_uninit)
- error (_("DWARF-2 expression error: DW_OP_reg operations must be "
- "used either alone or in conjunction with DW_OP_piece "
- "or DW_OP_bit_piece."));
+ dwarf_expr_require_composition (op_ptr, op_end, "DW_OP_reg");

result = op - DW_OP_reg0;
result_val = value_from_ulongest (address_type, result);
--
2.3.0