always read synthetic pointers as signed integers

I see the error message "access outside bounds of object referenced
via synthetic pointer" in the two fails below of mips gdb testing

print d[-2]^M
access outside bounds of object referenced via synthetic pointer^M
(gdb) FAIL: gdb.dwarf2/implptrconst.exp: print d[-2]
(gdb) print/d p[-1]^M
access outside bounds of object referenced via synthetic pointer^M
(gdb) FAIL: gdb.dwarf2/implptrpiece.exp: print/d p[-1]

in the first test, 'd[-2]' is processed by GDB as '* (&d[-2])'.  'd'
is a synthetic pointer, so its value is zero, the address of 'd[-2]'
is -2.  In dwarf2loc.c:indirect_pieced_value,

  /* This is an offset requested by GDB, such as value subscripts.
     However, due to how synthetic pointers are implemented, this is
     always presented to us as a pointer type.  This means we have to
     sign-extend it manually as appropriate.  */
  byte_offset = value_as_address (value);
  if (TYPE_LENGTH (value_type (value)) < sizeof (LONGEST))
    byte_offset = gdb_sign_extend (byte_offset,
				   8 * TYPE_LENGTH (value_type (value)));
  byte_offset += piece->v.ptr.offset;

We know that the value is really an offset instead of address, so the
fix is to extract the value as an (signed) offset.

gdb:

2015-01-08  Pedro Alves  <palves@redhat.com>
	    Yao Qi  <yao@codesourcery.com>

	* dwarf2loc.c (indirect_pieced_value): Don't call
	gdb_sign_extend.  Call extract_signed_integer instead.
	* utils.c (gdb_sign_extend): Remove.
	* utils.h (gdb_sign_extend): Remove declaration.

1 files changed, 11 insertions, 5 deletions

diff --git a/gdb/dwarf2loc.c b/gdb/dwarf2loc.c
index 2bd12d6..bdb2160 100644
--- a/gdb/dwarf2loc.c
+++ b/gdb/dwarf2loc.c
@@ -2012,6 +2012,7 @@ indirect_pieced_value (struct value *value)
   int i, bit_offset, bit_length;
   struct dwarf_expr_piece *piece = NULL;
   LONGEST byte_offset;
+  enum bfd_endian byte_order;
 
   type = check_typedef (value_type (value));
   if (TYPE_CODE (type) != TYPE_CODE_PTR)
@@ -2056,11 +2057,16 @@ indirect_pieced_value (struct value *value)
   /* This is an offset requested by GDB, such as value subscripts.
      However, due to how synthetic pointers are implemented, this is
      always presented to us as a pointer type.  This means we have to
-     sign-extend it manually as appropriate.  */
-  byte_offset = value_as_address (value);
-  if (TYPE_LENGTH (value_type (value)) < sizeof (LONGEST))
-    byte_offset = gdb_sign_extend (byte_offset,
-				   8 * TYPE_LENGTH (value_type (value)));
+     sign-extend it manually as appropriate.  Use raw
+     extract_signed_integer directly rather than value_as_address and
+     sign extend afterwards on architectures that would need it
+     (mostly everywhere except MIPS, which has signed addresses) as
+     the later would go through gdbarch_pointer_to_address and thus
+     return a CORE_ADDR with high bits set on architectures that
+     encode address spaces and other things in CORE_ADDR.  */
+  byte_order = gdbarch_byte_order (get_frame_arch (frame));
+  byte_offset = extract_signed_integer (value_contents (value),
+					TYPE_LENGTH (type), byte_order);
   byte_offset += piece->v.ptr.offset;
 
   gdb_assert (piece);