[PATCH 19/19] [INCOMPLETE] ARM: make return_address available for ARM_UNWIND
From: Dave Martin <hidden>
Date: 2013-01-28 12:50:36
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- 2013-01-25 · [PATCH 19/19] [INCOMPLETE] ARM: make return_address available for ARM_UNWIND · Arnd Bergmann <arnd@arndb.de>
On Mon, Jan 28, 2013 at 11:33:11AM +0900, Keun-O Park wrote:
Hello guys, Could you please review the patch of fixing bug first of returning wrong address when using frame pointer? I am wondering if the first patch is not delivered to the mailing.
I posted a similar patch to alkml a couple of months ago, but I got no response and it looks like I forgot about it. http://lists.infradead.org/pipermail/linux-arm-kernel/2012-November/129381.html [...]
quoted hunk ↗ jump to hunk
~~~~~~~~~~~~~~~~~~~~~snip~~~~~~~~~~~~~~~~~~~~~~~~~ From 3a60b536d22a2043d735c890a9aac9e7cb72de8f Mon Sep 17 00:00:00 2001 From: sahara <redacted> Date: Thu, 3 Jan 2013 17:12:37 +0900 Subject: [PATCH 1/2] arm: fix returning wrong CALLER_ADDRx This makes return_address return correct value for ftrace feature. unwind_frame does not update frame->lr but frame->pc for backtrace. And, the initialization for data.addr was missing so that wrong value returned when unwind_frame failed. Signed-off-by: sahara <redacted> --- arch/arm/kernel/return_address.c | 5 +++-- 1 files changed, 3 insertions(+), 2 deletions(-)diff --git a/arch/arm/kernel/return_address.c b/arch/arm/kernel/return_address.c index 8085417..fafedd8 100644 --- a/arch/arm/kernel/return_address.c +++ b/arch/arm/kernel/return_address.c@@ -26,7 +26,7 @@ static int save_return_addr(struct stackframe *frame, void *d) struct return_address_data *data = d; if (!data->level) { - data->addr = (void *)frame->lr; + data->addr = (void *)frame->pc; return 1; } else {@@ -41,7 +41,8 @@ void *return_address(unsigned int level) struct stackframe frame; register unsigned long current_sp asm ("sp"); - data.level = level + 1; + data.level = level + 2; + data.addr = NULL;
Can you explain why this is needed? I think I concluded it wasn't necessary, but you may be right -- I think if walk_stackframe() fails to unwind the next frame just after data.level reaches zero, then data.addr can remain unset and return_address() may return uninitialised garbage. Initialising data.addr to NULL before we start seems a good way to avoid that. Cheers ---Dave