gdb/rs6000: Read backchain as unsigned.

Previously, backchain was read as a signed quantity, resulting in
addresses like 0xfffffffffffeded0 instead of 0xfffeded0 returned by
unwinder on 32-bit powerpc.  While normally such addresses are masked
off, this causes problems for tracepoints, since 0xfffffffffffeded0
is considered unavailable.

Fixes a test failure in gdb.trace/entry-values.exp.

gdb/ChangeLog:

	* corefile.c (safe_read_memory_unsigned_integer): New function.
	* gdbcore.h (safe_read_memory_unsigned_integer): New prototype.
	* rs6000-tdep.c (rs6000_frame_cache): Read backchain as unsigned.

1 files changed, 18 insertions, 0 deletions

diff --git a/gdb/corefile.c b/gdb/corefile.c
index dbdbafc41f1..5ad4d40ec66 100644
--- a/gdb/corefile.c
+++ b/gdb/corefile.c
@@ -306,6 +306,24 @@ safe_read_memory_integer (CORE_ADDR memaddr, int len,
   return 1;
 }
 
+/* Read memory at MEMADDR of length LEN and put the contents in
+   RETURN_VALUE.  Return 0 if MEMADDR couldn't be read and non-zero
+   if successful.  */
+
+int
+safe_read_memory_unsigned_integer (CORE_ADDR memaddr, int len,
+				   enum bfd_endian byte_order,
+				   ULONGEST *return_value)
+{
+  gdb_byte buf[sizeof (ULONGEST)];
+
+  if (target_read_memory (memaddr, buf, len))
+    return 0;
+
+  *return_value = extract_unsigned_integer (buf, len, byte_order);
+  return 1;
+}
+
 LONGEST
 read_memory_integer (CORE_ADDR memaddr, int len,
 		     enum bfd_endian byte_order)