[PATCH] show_stack() portability and cleanup patch

From: David Mosberger <davidm@napali.hpl.hp.com>

This is an attempt at sanitizing the interface for stack trace dumping
somewhat.  It's basically the last thing which prevents 2.5.x from working
out-of-the-box for ia64.  ia64 apparently cannot reasonably implement the
show_stack interface declared in sched.h.

Here is the rationale: modern calling conventions don't maintain a frame
pointer and it's not possible to get a reliable stack trace with only a stack
pointer as the starting point.  You really need more machine state to start
with.  For a while, I thought the solution is to pass a task pointer to
show_stack(), but it turns out that this would negatively impact x86 because
it's sometimes useful to show only portions of a stack trace (e.g., starting
from the point at which a trap occurred).  Thus, this patch _adds_ the task
pointer instead:

 extern void show_stack(struct task_struct *tsk, unsigned long *sp);

The idea here is that show_stack(tsk, sp) will show the backtrace of task
"tsk", starting from the stack frame that "sp" is pointing to.  If tsk is
NULL, the trace will be for the current task.  If "sp" is NULL, all stack
frames of the task are shown.  If both are NULL, you'll get the full trace of
the current task.

I _think_ this should make everyone happy.

The patch also removes the declaration of show_trace() in linux/sched.h (it
never was a generic function; some platforms, in particular x86, may want to
update accordingly).

Finally, the patch replaces the one call to show_trace_task() with the
equivalent call show_stack(task, NULL).

The patch below is for Alpha and i386, since I can (compile-)test those (I'll
provide the ia64 update through my regular updates).  The other arches will
break visibly and updating the code should be trivial:

- add a task pointer argument to show_stack() and pass NULL as the first
  argument where needed

- remove show_trace_task()

- declare show_trace() in a platform-specific header file if you really
  want to keep it around

1 files changed, 7 insertions, 2 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index d313e2ccbf42..f5cdfefc5b05 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -148,10 +148,15 @@ extern void sched_init(void);
 extern void init_idle(task_t *idle, int cpu);
 
 extern void show_state(void);
-extern void show_trace(unsigned long *stack);
-extern void show_stack(unsigned long *stack);
 extern void show_regs(struct pt_regs *);
 
+/*
+ * TASK is a pointer to the task whose backtrace we want to see (or NULL for current
+ * task), SP is the stack pointer of the first frame that should be shown in the back
+ * trace (or NULL if the entire call-chain of the task should be shown).
+ */
+extern void show_stack(struct task_struct *task, unsigned long *sp);
+
 void io_schedule(void);
 long io_schedule_timeout(long timeout);