[PATCH] Default setting of the ARM_UNWIND option

[Claudio Scordino <claudio@evidence.eu.com>]

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[email cut-and-pasted from a private discussion...]
>>    moving from release 2.6.27 to release 2.6.32-rc4, my ARM board 
>> (derived from AT91SAM9623-EK) started hanging at the initial 
>> "Calibrating delay loop" message.
>>
>> After some inspection, I found out the problem to be with commit 
>> adf8b37bafc1495393201a2ae4235846371870d0.
>>
>> In practice, it enables stack unwinding support by default. However, if 
>> enabled, it hangs my machine.
>>
>> The problem might be with my compiler (according to the help, stack 
>> unwinding only works with EABI compilers).
>>
>> I'm using a CodeSourcery gcc 4.2.1 "arm-none-linux-gnueabi".
>>     
>
> I think 4.2.1 generates really buggy code with -fno-frame-pointer,
> nothing to do with the stack unwinding implementation in the kernel. I
> would recommend you either use a newer compiler or disables ARM_UNWIND
> in your .config (which automatically re-enables FRAMEPOINTER).
>   
Hi Catalin,

   thank you for your answer.

In my opinion, we should change the default setting of this option.

Having "yes" as default policy for ARM_UNWIND means that, by default, 
the kernel does not boot if a user has a buggy compiler (like me) and 
he/she doesn't explicitly disable the ARM_UNWIND option.

Consider that people may not know that their problem is related to the 
ARM_UNWIND option. Therefore, they may waste time just bisecting to 
understand where their problem really is.

Therefore, my suggestion is to change the default policy of this option 
as shown in the attached patch, to avoid a potential waste of time of 
developers. Users who know that they can enable this option, will enable 
it.

Let me know what you think about this suggestion.

Many thanks and my best regards,

               Claudio



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>From 3b688dbebb5fb3345e48cd491eb387434db165da Mon Sep 17 00:00:00 2001
From: Claudio Scordino <claudio@evidence.eu.com>
Date: Mon, 19 Oct 2009 11:59:16 +0200
Subject: [PATCH 1/1] Disable stack unwinding support by default, since it does not work on some buggy or not-EABI compilers.


Signed-off-by: Claudio Scordino <claudio@evidence.eu.com>
---
 arch/arm/Kconfig.debug |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug
index 1a6f70e..925e3fd 100644
--- a/arch/arm/Kconfig.debug
+++ b/arch/arm/Kconfig.debug
@@ -19,13 +19,13 @@ config FRAME_POINTER
 config ARM_UNWIND
 	bool "Enable stack unwinding support"
 	depends on AEABI && EXPERIMENTAL
-	default y
+	default n
 	help
 	  This option enables stack unwinding support in the kernel
 	  using the information automatically generated by the
 	  compiler. The resulting kernel image is slightly bigger but
 	  the performance is not affected. Currently, this feature
-	  only works with EABI compilers. If unsure say Y.
+	  only works with EABI compilers. If unsure say N.
 
 config DEBUG_USER
 	bool "Verbose user fault messages"
-- 
1.6.0.4