[PATCH 2/2] process: change from __backtrace to dump_stack_regs in show_regs

On Wed, August 24, 2011 11:57 am, Nicolas Pitre wrote:

On Wed, 24 Aug 2011, Laura Abbott wrote:

quoted

Currently, show_regs calls __backtrace which does
nothing if CONIFG_FRAME_POINTER is not set. Switch to

s/CONIFG/CONFIG/

quoted

dump_stack_regs to show the backtrace from a given
set of registers.

Signed-off-by: Laura Abbott <redacted>
---
 arch/arm/kernel/process.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
index 1a347f4..6f11213 100644
--- a/arch/arm/kernel/process.c
+++ b/arch/arm/kernel/process.c

@@ -319,7 +319,7 @@ void show_regs(struct pt_regs * regs)
 	printk("\n");
 	printk("Pid: %d, comm: %20s\n", task_pid_nr(current), current->comm);
 	__show_regs(regs);
-	__backtrace();
+	dump_stack_regs(regs);

This is not equivalent.  A call to __backtrace() will display a call
trace leading to this show_regs().  Given that you defined
dump_stack_regs(regs) as dump_backtrace(regs, NULL), the trace will
instead contain calls leading up to the point where those regs were
saved.

Do other architectures show the call stack to show_regs? From my reading
of other code (x86, ppc) it seems like if show_regs generates a call stack
it generates a call stack based off of the saved registers unless I'm
drastically misunderstanding the code. Generating a call stack based off
of not saved registers seems inconsistent with the rest of show_regs which
shows saved state.

A better way to achieve what you want would be:

- remove the __backtrace entry point from lib/backtrace.S

- define __backtrace() in kernel/traps.c as a call to
  dump_backtrace(NULL, NULL) which will have the same effect as the
  assembly code for __backtrace().

- realize that dump_stack() is already doing exactly that, therefore...

- use dump_stack() in show_regs() which is the only caller of
  __backtrace and get rid of __backtrace entirely.

Obviously the above can be collapsed in one patch.


Nicolas

Laura

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