[PATCH] GUD-MI's disassembly buffer should follow $PC in the absence of debug information.

[Kaushik Srenevasan <ksrenevasan@gmail.com>]

All,

GUD-MI's disassembly buffer only works when the current frame has debug
information. While debugging dynamically generated code it'd be useful
to simply follow the program counter. I understand that newer GDBs
expose an API that lets a JIT compiler register debug information for
dynamically generated code, but JITs typically only do so for real
functions. So, having the disassembly buffer follow $PC would still be
useful while stepping through dynamically generated, shorter sequences
of code (like call stubs, inline caches etc.). 

The latest GDB (7.4.50.20120122-cvs) does this in its TUI mode while my
stable GDB's (7.0.1-debian) behavior is the same as Emacs 23 GUD.

Please review and merge.

         Thanks,
            -Kaushik

=== modified file 'lisp/progmodes/gdb-mi.el'
--- lisp/progmodes/gdb-mi.el	2012-01-05 09:46:05 +0000
+++ lisp/progmodes/gdb-mi.el	2012-01-24 05:13:10 +0000
@@ -3259,8 +3259,12 @@
   (let* ((frame (gdb-current-buffer-frame))
          (file (bindat-get-field frame 'fullname))
          (line (bindat-get-field frame 'line)))
-    (when file
-      (format "-data-disassemble -f %s -l %s -n -1 -- 0" file line)))
+    (if file
+      (format "-data-disassemble -f %s -l %s -n -1 -- 0" file line)
+    ;; If we're unable to get a file name / line for $PC, simply
+    ;; follow $PC, disassembling the next 10 (x ~15 (on IA) ==
+    ;; 150 bytes) instructions.
+    "-data-disassemble -s $pc -e \"$pc + 150\" -- 0"))
   gdb-disassembly-handler
   ;; We update disassembly only after we have actual frame information
   ;; about all threads, so no there's `update' signal in this list
@@ -3319,8 +3323,12 @@
       (gdb-table-add-row table
                          (list
                           (bindat-get-field instr 'address)
-                          (apply #'format "<%s+%s>:"
-                                 (gdb-get-many-fields instr 'func-name 'offset))
+                          (let
+                              ((func-name (bindat-get-field instr 'func-name))
+                               (offset (bindat-get-field instr 'offset)))
+                            (if func-name
+                                (format "<%s+%s>:" func-name offset)
+                              ""))
                           (bindat-get-field instr 'inst)))
       (when (string-equal (bindat-get-field instr 'address)
                           address)