Delegate to target_ops->beneath for TARGET_OBJECT_RAW_MEMORY

GDB on x86_64-linux is unable to disassemble on core-file target.

$ ./gdb ./testsuite/gdb.base/corefile
(gdb) core-file ./testsuite/gdb.base/corefile.core
(gdb) disassemble main
Dump of assembler code for function main:
   0x0000000000400976 <+0>:	Cannot access memory at address 0x400976

However, it works if we turn code-cache off.

(gdb) set code-cache off
(gdb) disassemble main,+4
Dump of assembler code from 0x400976 to 0x40097a:
   0x0000000000400976 <main+0>:	push   %rbp
   0x0000000000400977 <main+1>:	mov    %rsp,%rbp
End of assembler dump.

When code-cache is off, GDB will iterate target_ops from top to bottom
and call to_xfer_partial.  When current_target is "core", it will call
to_xfer_partial of target "exec", which reads the contents for
disassemble.  However, dcache uses TARGET_OBJECT_RAW_MEMORY to read,
but target_xfer_partial doesn't delegate requests to beneath for
TARGET_OBJECT_RAW_MEMORY.

This patch factors out the iteration from top to bottom to a new
function, raw_memory_xfer_partial, and use it for
TARGET_OBJECT_RAW_MEMORY.

Regression tested on x86_64-linux.

gdb:

2013-11-29  Yao Qi  <yao@codesourcery.com>
	    Pedro Alves  <palves@redhat.com>

	* dcache.c (dcache_read_line): Use current_target.beneath
	instead of &current_target.
	* target.c (memory_xfer_partial_1): Factor code out to ...
	(raw_memory_xfer_partial): ... it.  New function.
	(target_xfer_partial): Call raw_memory_xfer_partial if OBJECT
	is TARGET_OBJECT_RAW_MEMORY.

1 files changed, 2 insertions, 2 deletions

diff --git a/gdb/dcache.c b/gdb/dcache.c
index ea2b73230c..12d1a4b9c2 100644
--- a/gdb/dcache.c
+++ b/gdb/dcache.c
@@ -336,8 +336,8 @@ dcache_read_line (DCACHE *dcache, struct dcache_block *db)
 	  len     -= reg_len;
 	  continue;
 	}
-      
-      res = target_read (&current_target, TARGET_OBJECT_RAW_MEMORY,
+
+      res = target_read (current_target.beneath, TARGET_OBJECT_RAW_MEMORY,
 			 NULL, myaddr, memaddr, reg_len);
       if (res < reg_len)
 	return 0;