[patch] allow switching stacks

[Jim Houston <jim.houston@comcast.net>]

Hi Everyone,

This patch against gdb-6.0 adds an option to disable an error check
which reports a non-contiguous stack as corrupted. I need this
option to get a reliable stack trace using kgdb on the x86-64 Linux
kernel because it uses a separate per-processor interrupt stack.

This option is enabled with:

     set backtrace switch-stacks on

Jim Houston - Concurrent Computer Corp.

-

diff -urN old/gdb-6.0/gdb/frame.c new/gdb-6.0/gdb/frame.c
--- old/gdb-6.0/gdb/frame.c	2003-12-31 15:27:45.866840920 -0500
+++ new/gdb-6.0/gdb/frame.c	2003-12-31 15:27:58.310949128 -0500
@@ -138,6 +138,7 @@
 /* Flag to indicate whether backtraces should stop at main et.al.  */
 
 static int backtrace_past_main;
+static int backtrace_switch_stacks;
 static unsigned int backtrace_limit = UINT_MAX;
 
 
@@ -1971,7 +1972,7 @@
      the next frame.  This happens when a frame unwind goes backwards.
      Since the sentinel frame doesn't really exist, don't compare the
      inner-most against that sentinel.  */
-  if (this_frame->level > 0
+  if (!backtrace_switch_stacks && this_frame->level > 0
       && frame_id_inner (get_frame_id (this_frame),
 			 get_frame_id (this_frame->next)))
     error ("Previous frame inner to this frame (corrupt stack?)");
@@ -2461,6 +2462,19 @@
 			   NULL, NULL, &set_backtrace_cmdlist,
 			   &show_backtrace_cmdlist);
 
+  add_setshow_boolean_cmd ("switch-stacks", class_obscure,
+			   &backtrace_switch_stacks, "\
+Set if thread may use multiple stacks.  This flag disables checks in\n\
+the stack trace which expect that the stack grew in a consistent direction.\n\
+This option is needed for kernel debug when the kernel has separate\n\
+process and interrupt stacks.", "\
+Show if thread may use multiple stacks.  This flag disables checks in\n\
+the stack trace which expect that the stack grew in a consistent direction.\n\
+This option is needed for kernel debug when the kernel has separate\n\
+process and interrupt stacks.",
+			   NULL, NULL, &set_backtrace_cmdlist,
+			   &show_backtrace_cmdlist);
+
   add_setshow_uinteger_cmd ("limit", class_obscure,
 			    &backtrace_limit, "\
 Set an upper bound on the number of backtrace levels.\n\