PR gdb/10565

	* value.c (value_primitive_field): Do not save value_offset for
	bitfields.
	(unpack_bits_as_long): Do not read an entire ULONGEST.

	testsuite/
	PR gdb/10565

	* gdb.base/bitfields.c (struct container, container): New.
	(main): Initialize it and call break5.
	* gdb.base/bitfields.exp (bitfield_at_offset): New test.

1 files changed, 12 insertions, 4 deletions

diff --git a/gdb/value.c b/gdb/value.c
index 330ab156956..f26e16c7d62 100644
--- a/gdb/value.c
+++ b/gdb/value.c
@@ -1878,7 +1878,7 @@ value_primitive_field (struct value *arg1, int offset,
 	v->bitpos = bitpos % container_bitsize;
       else
 	v->bitpos = bitpos % 8;
-      v->offset = value_offset (arg1) + value_embedded_offset (arg1)
+      v->offset = value_embedded_offset (arg1)
 	+ (bitpos - v->bitpos) / 8;
       v->parent = arg1;
       value_incref (v->parent);
@@ -2031,15 +2031,23 @@ unpack_bits_as_long (struct type *field_type, const gdb_byte *valaddr,
   ULONGEST val;
   ULONGEST valmask;
   int lsbcount;
+  int bytes_read;
 
-  val = extract_unsigned_integer (valaddr + bitpos / 8,
-				  sizeof (val), byte_order);
+  /* Read the minimum number of bytes required; there may not be
+     enough bytes to read an entire ULONGEST.  */
   CHECK_TYPEDEF (field_type);
+  if (bitsize)
+    bytes_read = ((bitpos % 8) + bitsize + 7) / 8;
+  else
+    bytes_read = TYPE_LENGTH (field_type);
+
+  val = extract_unsigned_integer (valaddr + bitpos / 8,
+				  bytes_read, byte_order);
 
   /* Extract bits.  See comment above. */
 
   if (gdbarch_bits_big_endian (get_type_arch (field_type)))
-    lsbcount = (sizeof val * 8 - bitpos % 8 - bitsize);
+    lsbcount = (bytes_read * 8 - bitpos % 8 - bitsize);
   else
     lsbcount = (bitpos % 8);
   val >>= lsbcount;