gdb: dwarf2 generic implementation for caching function data

When there is no dwarf2 data for a register, a function can be called
to provide the value of this register.  In some situations, it might
not be trivial to determine the value to return and it would cause a
performance bottleneck to do the computation each time.

This patch allows the called function to have a "cache" object that it
can use to store some metadata between calls to reduce the performance
impact of the complex logic.

The cache object is unique for each function and frame, so if there are
more than one function pointer stored in the dwarf2_frame_cache->reg
array, then the appropriate pointer will be supplied (the type is not
known by the dwarf2 implementation).

dwarf2_frame_get_fn_data can be used to retrieve the function unique
cache object.
dwarf2_frame_allocate_fn_data can be used to allocate and retrieve the
function unique cache object.

Signed-off-by: Torbjörn SVENSSON <torbjorn.svensson@foss.st.com>
Signed-off-by: Yvan Roux <yvan.roux@foss.st.com>

1 files changed, 35 insertions, 2 deletions

diff --git a/gdb/dwarf2/frame.h b/gdb/dwarf2/frame.h
index 4444c15..5643e55 100644
--- a/gdb/dwarf2/frame.h
+++ b/gdb/dwarf2/frame.h
@@ -66,6 +66,9 @@ enum dwarf2_frame_reg_rule
 
 /* Register state.  */
 
+typedef struct value *(*fn_prev_register) (frame_info_ptr this_frame,
+					   void **this_cache, int regnum);
+
 struct dwarf2_frame_state_reg
 {
   /* Each register save state can be described in terms of a CFA slot,
@@ -78,8 +81,7 @@ struct dwarf2_frame_state_reg
       const gdb_byte *start;
       ULONGEST len;
     } exp;
-    struct value *(*fn) (frame_info_ptr this_frame, void **this_cache,
-			 int regnum);
+    fn_prev_register fn;
   } loc;
   enum dwarf2_frame_reg_rule how;
 };
@@ -262,4 +264,35 @@ extern int dwarf2_fetch_cfa_info (struct gdbarch *gdbarch, CORE_ADDR pc,
 				  const gdb_byte **cfa_start_out,
 				  const gdb_byte **cfa_end_out);
 
+
+/* Allocate a new instance of the function unique data.
+
+   The main purpose of this custom function data object is to allow caching the
+   value of expensive lookups in the prev_register implementation.
+
+   THIS_FRAME is the frame that the custom data object should be associated
+   with.
+   THIS_CACHE is the dwarf2 cache object to store the pointer on.
+   COOKIE is the key for the prev_function implementation.
+   SIZE is the size of the custom data object to allocate.  */
+
+extern void *dwarf2_frame_allocate_fn_data (frame_info_ptr this_frame,
+					    void **this_cache,
+					    fn_prev_register cookie,
+					    unsigned long size);
+
+/* Retrieve the function unique data for this frame or NULL if none exists.
+
+   The main purpose of this custom function data object is to allow caching the
+   value of expensive lookups in the prev_register implementation.
+
+   THIS_FRAME is the frame that the custom data object should be associated
+   with.
+   THIS_CACHE is the dwarf2 cache object to store the pointer on.
+   COOKIE is the key for the prev_function implementation.  */
+
+extern void *dwarf2_frame_get_fn_data (frame_info_ptr this_frame,
+				       void **this_cache,
+				       fn_prev_register cookie);
+
 #endif /* dwarf2-frame.h */