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, 19 insertions, 4 deletions

diff --git a/gdb/target.c b/gdb/target.c
index f402a18..cc6194b 100644
--- a/gdb/target.c
+++ b/gdb/target.c
@@ -1547,7 +1547,8 @@ memory_xfer_partial_1 (struct target_ops *ops, enum target_object object,
 	 the collected memory range fails.  */
       && get_traceframe_number () == -1
       && (region->attrib.cache
-	  || (stack_cache_enabled_p () && object == TARGET_OBJECT_STACK_MEMORY)))
+	  || (stack_cache_enabled_p () && object == TARGET_OBJECT_STACK_MEMORY)
+	  || (code_cache_enabled_p () && object == TARGET_OBJECT_CODE_MEMORY)))
     {
       DCACHE *dcache = target_dcache_get_or_init ();
 
@@ -1600,8 +1601,8 @@ memory_xfer_partial_1 (struct target_ops *ops, enum target_object object,
       && writebuf != NULL
       && target_dcache_init_p ()
       && !region->attrib.cache
-      && stack_cache_enabled_p ()
-      && object != TARGET_OBJECT_STACK_MEMORY)
+      && ((stack_cache_enabled_p () && object != TARGET_OBJECT_STACK_MEMORY)
+	  || (code_cache_enabled_p () && object != TARGET_OBJECT_CODE_MEMORY)))
     {
       DCACHE *dcache = target_dcache_get ();
 
@@ -1697,7 +1698,8 @@ target_xfer_partial (struct target_ops *ops,
   /* If this is a memory transfer, let the memory-specific code
      have a look at it instead.  Memory transfers are more
      complicated.  */
-  if (object == TARGET_OBJECT_MEMORY || object == TARGET_OBJECT_STACK_MEMORY)
+  if (object == TARGET_OBJECT_MEMORY || object == TARGET_OBJECT_STACK_MEMORY
+      || object == TARGET_OBJECT_CODE_MEMORY)
     retval = memory_xfer_partial (ops, object, readbuf,
 				  writebuf, offset, len);
   else
@@ -1799,6 +1801,19 @@ target_read_stack (CORE_ADDR memaddr, gdb_byte *myaddr, ssize_t len)
     return TARGET_XFER_E_IO;
 }
 
+/* Like target_read_memory, but specify explicitly that this is a read from
+   the target's code.  This may trigger different cache behavior.  */
+
+int
+target_read_code (CORE_ADDR memaddr, gdb_byte *myaddr, ssize_t len)
+{
+  if (target_read (current_target.beneath, TARGET_OBJECT_CODE_MEMORY, NULL,
+		   myaddr, memaddr, len) == len)
+    return 0;
+  else
+    return TARGET_XFER_E_IO;
+}
+
 /* Write LEN bytes from MYADDR to target memory at address MEMADDR.
    Returns either 0 for success or a target_xfer_error value if any
    error occurs.  If an error occurs, no guarantee is made about how