[binutils-gdb] read/write_pieced_value: Respect value parent's offset

[Andreas Arnez <arnez at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=af547a9614969e1d1ea6fcec6b59cd77a606380f

commit af547a9614969e1d1ea6fcec6b59cd77a606380f
Author: Andreas Arnez <arnez@linux.vnet.ibm.com>
Date:   Tue Jun 13 15:20:27 2017 +0200

    read/write_pieced_value: Respect value parent's offset
    
    In the case of targeting a bit-field, read_pieced_value and
    write_pieced_value calculate the number of bits preceding the bit-field
    without considering the relative offset of the value's parent.  This is
    relevant for a structure variable like this:
    
      struct s {
          uint64_t foo;
          struct {
    	  uint32_t bar;
    	  uint32_t bf : 10;  /* <-- target bit-field */
          } baz;
      } s;
    
    In this scenario, if 'val' is a GDB value representing s.baz.bf,
    val->parent represents the whole s.baz structure, and the following holds:
    
      - value_offset (val) == sizeof s.baz.bar == 4
      - value_offset (val->parent) == sizeof s.foo == 8
    
    The current logic would only use value_offset(val), resulting in the wrong
    offset into the target value.  This is fixed.
    
    gdb/ChangeLog:
    
    	* dwarf2loc.c (read_pieced_value): Respect parent value's offset
    	when targeting a bit-field.
    	(write_pieced_value): Likewise.

Diff:
---
 gdb/ChangeLog   | 6 ++++++
 gdb/dwarf2loc.c | 6 ++++--
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index bd46425..4b22676 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,5 +1,11 @@
 2017-06-13  Andreas Arnez  <arnez@linux.vnet.ibm.com>
 
+	* dwarf2loc.c (read_pieced_value): Respect parent value's offset
+	when targeting a bit-field.
+	(write_pieced_value): Likewise.
+
+2017-06-13  Andreas Arnez  <arnez@linux.vnet.ibm.com>
+
 	* dwarf2loc.c (struct piece_closure) <addr_size>: Remove field.
 	(allocate_piece_closure): Drop addr_size parameter.
 	(dwarf2_evaluate_loc_desc_full): Adjust call to
diff --git a/gdb/dwarf2loc.c b/gdb/dwarf2loc.c
index 8f99844..6ce2993 100644
--- a/gdb/dwarf2loc.c
+++ b/gdb/dwarf2loc.c
@@ -1776,7 +1776,8 @@ read_pieced_value (struct value *v)
   bits_to_skip = 8 * value_offset (v);
   if (value_bitsize (v))
     {
-      bits_to_skip += value_bitpos (v);
+      bits_to_skip += (8 * value_offset (value_parent (v))
+		       + value_bitpos (v));
       type_len = value_bitsize (v);
     }
   else
@@ -1946,7 +1947,8 @@ write_pieced_value (struct value *to, struct value *from)
   bits_to_skip = 8 * value_offset (to);
   if (value_bitsize (to))
     {
-      bits_to_skip += value_bitpos (to);
+      bits_to_skip += (8 * value_offset (value_parent (to))
+		       + value_bitpos (to));
       type_len = value_bitsize (to);
     }
   else