Re: [patch] allow switching stacks

[Michael Snyder <msnyder@redhat.com>]

Jim Houston wrote:
> 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

Good idea, and nice implementation.  My only suggestions are in
the user interface realm.  I'm thinking something like
"non-contiguous stacks" would be more meaningful than "multiple
stacks" (there's really still only one stack, it's just broken
into two segments).  Same goes for switch-stacks; it's a bit
non-intuitive to me.  segmented-stack?  discontiguous-stack?

> 
> 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\
>