[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, 10 insertions, 7 deletions

diff --git a/arch/ppc64/kernel/process.c b/arch/ppc64/kernel/process.c
index 949425d44cb3..c22a54fe544f 100644
--- a/arch/ppc64/kernel/process.c
+++ b/arch/ppc64/kernel/process.c
@@ -129,7 +129,6 @@ struct task_struct *__switch_to(struct task_struct *prev,
 	return last;
 }
 
-static void show_tsk_stack(struct task_struct *p, unsigned long sp);
 char *ppc_find_proc_name(unsigned *p, char *buf, unsigned buflen);
 
 void show_regs(struct pt_regs * regs)
@@ -172,7 +171,7 @@ void show_regs(struct pt_regs * regs)
 	printk("NIP [%016lx] ", regs->nip);
 	printk("%s\n", ppc_find_proc_name((unsigned *)regs->nip,
 	       name_buf, 256));
-	show_tsk_stack(current, regs->gpr[1]);
+	show_stack(current, (unsigned long *)regs->gpr[1]);
 }
 
 void exit_thread(void)
@@ -517,22 +516,26 @@ unsigned long get_wchan(struct task_struct *p)
 	return 0;
 }
 
-static void show_tsk_stack(struct task_struct *p, unsigned long sp)
+void show_stack(struct task_struct *p, unsigned long *_sp)
 {
 	unsigned long ip;
 	unsigned long stack_page = (unsigned long)p->thread_info;
 	int count = 0;
 	char name_buf[256];
+	unsigned long sp = (unsigned long)_sp;
 
 	if (!p)
 		return;
 
+	if (sp == 0)
+		sp = p->thread.ksp;
 	printk("Call Trace:\n");
 	do {
 		if (__get_user(sp, (unsigned long *)sp))
 			break;
-		if (sp < (stack_page + sizeof(struct thread_struct)) ||
-		    sp >= (stack_page + THREAD_SIZE))
+		if (sp < stack_page + sizeof(struct thread_struct))
+			break;
+		if (sp >= stack_page + THREAD_SIZE)
 			break;
 		if (__get_user(ip, (unsigned long *)(sp + 16)))
 			break;
@@ -544,10 +547,10 @@ static void show_tsk_stack(struct task_struct *p, unsigned long sp)
 
 void dump_stack(void)
 {
-	show_tsk_stack(current, (unsigned long)_get_SP());
+	show_stack(current, (unsigned long *)_get_SP());
 }
 
 void show_trace_task(struct task_struct *tsk)
 {
-	show_tsk_stack(tsk, tsk->thread.ksp);
+	show_stack(tsk, (unsigned long *)tsk->thread.ksp);
 }