set/show code-cache

Similar to stack cache, in this patch, we add
TARGET_OBJECT_CODE_MEMORY to read code from target and add a new
option "set code-cache on|off" to optimize code accesses by
using the target memory cache.

In V4:
 - Remove "without affecting correctness" from NEWS and doc.
 - Replace "ON" with "on" in doc.
 - "access" -> "accesses".

In V3:
 - Rename functions and variables.
 - Update command help, doc and NEWS entry.
 - Invalidate cache on option transitions, to align with
   the behaviour of "stack-cache".  Since cache invalidation is
   transparent to users, users don't know option "stack-cache"
   transitions cause code cache invalidation.

V2 was reviewed by Doug.  There are some changes in V3, so I post it
here.

gdb:

2013-11-24  Yao Qi  <yao@codesourcery.com>

	* NEWS: Add note on new "set code-cache" option.
	* target-dcache.c (code_cache_enabled_1): New variable.
	(code_cache_enabled): New variable.
	(show_code_cache, set_code_cache): New function.
	(code_cache_enabled_p): New function.
	(_initialize_target_dcache): Register command.
	* target-dcache.h (code_cache_enabled_p): Declare.
	* target.c (memory_xfer_partial_1):Handle
	TARGET_OBJECT_CODE_MEMORY and code_cache_enabled.
	(target_read_code): New function.
	* target.h (enum target_object) <TARGET_OBJECT_CODE_MEMORY>:
	New.
	(target_read_code): Declare.

gdb/doc:

2013-11-24  Yao Qi  <yao@codesourcery.com>

	* gdb.texinfo (Caching Remote Data): Document new
	"set/show stack-cache" option.

1 files changed, 52 insertions, 0 deletions

diff --git a/gdb/target-dcache.c b/gdb/target-dcache.c
index 6b7986a..7f68ddc 100644
--- a/gdb/target-dcache.c
+++ b/gdb/target-dcache.c
@@ -124,6 +124,46 @@ stack_cache_enabled_p (void)
   return stack_cache_enabled;
 }
 
+/* The option sets this.  */
+
+static int code_cache_enabled_1 = 1;
+
+/* And set_code_cache updates this.
+   The reason for the separation is so that we don't flush the cache for
+   on->on transitions.  */
+static int code_cache_enabled = 1;
+
+/* This is called *after* the code-cache has been set.
+   Flush the cache for off->on and on->off transitions.
+   There's no real need to flush the cache for on->off transitions,
+   except cleanliness.  */
+
+static void
+set_code_cache (char *args, int from_tty, struct cmd_list_element *c)
+{
+  if (code_cache_enabled != code_cache_enabled_1)
+    target_dcache_invalidate ();
+
+  code_cache_enabled = code_cache_enabled_1;
+}
+
+/* Show option "code-cache".  */
+
+static void
+show_code_cache (struct ui_file *file, int from_tty,
+		 struct cmd_list_element *c, const char *value)
+{
+  fprintf_filtered (file, _("Cache use for code accesses is %s.\n"), value);
+}
+
+/* Return true if "code cache" is enabled, otherwise, return false.  */
+
+int
+code_cache_enabled_p (void)
+{
+  return code_cache_enabled;
+}
+
 /* -Wmissing-prototypes */
 extern initialize_file_ftype _initialize_target_dcache;
 
@@ -141,6 +181,18 @@ By default, caching for stack access is on."),
 			   show_stack_cache,
 			   &setlist, &showlist);
 
+  add_setshow_boolean_cmd ("code-cache", class_support,
+			   &code_cache_enabled_1, _("\
+Set cache use for code segment access."), _("\
+Show cache use for code segment access."), _("\
+When on, use the target memory cache for all code segment accesses,\n\
+regardless of any configured memory regions.  This improves remote\n\
+performance significantly.  By default, caching for code segment\n\
+access is on."),
+			   set_code_cache,
+			   show_code_cache,
+			   &setlist, &showlist);
+
   target_dcache_aspace_key
     = register_address_space_data_with_cleanup (NULL,
 						target_dcache_cleanup);