commit 359b19bb24d048750aa5367ad56a33267300d1a8
Author: Andreas Arnez <arnez@linux.vnet.ibm.com>
Date:   Tue Jun 13 15:20:28 2017 +0200

    write_pieced_value: Transfer least significant bits into bit-field
    
    On big-endian targets, when targeting a bit-field, write_pieced_value
    currently transfers the source value's *most* significant bits to the
    target value, instead of its least significant bits.  This is fixed.
    
    In particular the fix adjusts the initial value of 'offset', which can now
    potentially be nonzero.  Thus the variable 'type_len' is renamed to
    'max_offset', to avoid confusion.  And for consistency, the affected logic
    that was mirrored in read_pieced_value is changed there in the same way.
    
    gdb/ChangeLog:
    
            * dwarf2loc.c (write_pieced_value): When writing to a bit-field,
            transfer the source value's least significant bits, instead of its
            lowest-addressed ones.  Rename type_len to max_offset.
            (read_pieced_value): Mirror above changes to write_pieced_value as
            applicable.

### a/gdb/ChangeLog
### b/gdb/ChangeLog
## -1,5 +1,13 @@
 2017-06-13  Andreas Arnez  <arnez@linux.vnet.ibm.com>
 
+	* dwarf2loc.c (write_pieced_value): When writing to a bit-field,
+	transfer the source value's least significant bits, instead of its
+	lowest-addressed ones.  Rename type_len to max_offset.
+	(read_pieced_value): Mirror above changes to write_pieced_value as
+	applicable.
+
+2017-06-13  Andreas Arnez  <arnez@linux.vnet.ibm.com>
+
 	* dwarf2loc.c (write_pieced_value): In DWARF_VALUE_MEMORY,
 	truncate full bytes from dest_offset_bits before using it as an
 	offset into the buffer.
--- a/gdb/dwarf2loc.c
+++ b/gdb/dwarf2loc.c
@@ -1756,12 +1756,11 @@ static void
 read_pieced_value (struct value *v)
 {
   int i;
-  long offset = 0;
+  LONGEST offset = 0, max_offset;
   ULONGEST bits_to_skip;
   gdb_byte *contents;
   struct piece_closure *c
     = (struct piece_closure *) value_computed_closure (v);
-  size_t type_len;
   size_t buffer_size = 0;
   std::vector<gdb_byte> buffer;
   int bits_big_endian
@@ -1778,12 +1777,12 @@ read_pieced_value (struct value *v)
     {
       bits_to_skip += (8 * value_offset (value_parent (v))
 		       + value_bitpos (v));
-      type_len = value_bitsize (v);
+      max_offset = value_bitsize (v);
     }
   else
-    type_len = 8 * TYPE_LENGTH (value_type (v));
+    max_offset = 8 * TYPE_LENGTH (value_type (v));
 
-  for (i = 0; i < c->n_pieces && offset < type_len; i++)
+  for (i = 0; i < c->n_pieces && offset < max_offset; i++)
     {
       struct dwarf_expr_piece *p = &c->pieces[i];
       size_t this_size, this_size_bits;
@@ -1798,20 +1797,13 @@ read_pieced_value (struct value *v)
 	  bits_to_skip -= this_size_bits;
 	  continue;
 	}
-      if (bits_to_skip > 0)
-	{
-	  dest_offset_bits = 0;
-	  source_offset_bits = bits_to_skip;
-	  this_size_bits -= bits_to_skip;
-	  bits_to_skip = 0;
-	}
-      else
-	{
-	  dest_offset_bits = offset;
-	  source_offset_bits = 0;
-	}
-      if (this_size_bits > type_len - offset)
-	this_size_bits = type_len - offset;
+      source_offset_bits = bits_to_skip;
+      this_size_bits -= bits_to_skip;
+      bits_to_skip = 0;
+      dest_offset_bits = offset;
+
+      if (this_size_bits > max_offset - offset)
+	this_size_bits = max_offset - offset;
 
       this_size = (this_size_bits + source_offset_bits % 8 + 7) / 8;
       source_offset = source_offset_bits / 8;
@@ -1932,12 +1924,11 @@ static void
 write_pieced_value (struct value *to, struct value *from)
 {
   int i;
-  long offset = 0;
   ULONGEST bits_to_skip;
+  LONGEST offset = 0, max_offset;
   const gdb_byte *contents;
   struct piece_closure *c
     = (struct piece_closure *) value_computed_closure (to);
-  size_t type_len;
   size_t buffer_size = 0;
   std::vector<gdb_byte> buffer;
   int bits_big_endian
@@ -1949,12 +1940,20 @@ write_pieced_value (struct value *to, struct value *from)
     {
       bits_to_skip += (8 * value_offset (value_parent (to))
 		       + value_bitpos (to));
-      type_len = value_bitsize (to);
-    }
+      /* Use the least significant bits of FROM.  */
+      if (gdbarch_byte_order (get_type_arch (value_type (from)))
+	  == BFD_ENDIAN_BIG)
+	{
+	  max_offset = 8 * TYPE_LENGTH (value_type (from));
+	  offset = max_offset - value_bitsize (to);
+	}
+      else
+	max_offset = value_bitsize (to);
+   }
   else
-    type_len = 8 * TYPE_LENGTH (value_type (to));
+    max_offset = 8 * TYPE_LENGTH (value_type (to));
 
-  for (i = 0; i < c->n_pieces && offset < type_len; i++)
+  for (i = 0; i < c->n_pieces && offset < max_offset; i++)
     {
       struct dwarf_expr_piece *p = &c->pieces[i];
       size_t this_size_bits, this_size;
@@ -1968,20 +1967,13 @@ write_pieced_value (struct value *to, struct value *from)
 	  bits_to_skip -= this_size_bits;
 	  continue;
 	}
-      if (bits_to_skip > 0)
-	{
-	  dest_offset_bits = bits_to_skip;
-	  source_offset_bits = 0;
-	  this_size_bits -= bits_to_skip;
-	  bits_to_skip = 0;
-	}
-      else
-	{
-	  dest_offset_bits = 0;
-	  source_offset_bits = offset;
-	}
-      if (this_size_bits > type_len - offset)
-	this_size_bits = type_len - offset;
+      dest_offset_bits = bits_to_skip;
+      this_size_bits -= bits_to_skip;
+      bits_to_skip = 0;
+      source_offset_bits = offset;
+
+      if (this_size_bits > max_offset - offset)
+	this_size_bits = max_offset - offset;
 
       this_size = (this_size_bits + dest_offset_bits % 8 + 7) / 8;
       source_offset = source_offset_bits / 8;