Message-ID: <4AE82CDC.4080409@evidence.eu.com>
Date: Wed, 28 Oct 2009 12:37:00 +0100
From: Claudio Scordino <claudio@evidence.eu.com>
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To: Catalin Marinas <catalin.marinas@arm.com>
CC: linux-kernel@vger.kernel.org, rmk+kernel@arm.linux.org.uk,
       linux-arm-kernel@lists.arm.linux.org.uk, akpm@linux-foundation.org
Subject: Re: [PATCH][RE-SUBMIT] Default setting of the ARM_UNWIND option
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Catalin Marinas ha scritto:
> On Mon, 2009-10-26 at 09:27 +0100, Claudio Scordino wrote:
>   
>> My ARM board hanged at the initial "Calibrating delay loop" message.
>>
>> After some inspection, I found out the problem to be with commit
>> adf8b37bafc1495393201a2ae4235846371870d0. This commit introduces stack
>> unwinding for ARM, and set it enabled by default. However, it seems to
>> not work with buggy or not-EABI compilers.
>>
>> My suggestion is to keep the feature (which is fine) but change the
>> default setting of the option (see the attached patch).
>>     
>
> The option still depends on EXPERIMENTAL, so you get ARM_UNWIND on when
> enabling that.
>
> I'm more in favour of a #warning on #error in the unwind.c file based on
> the compiler version rather than not having it on by default. The reason
> is that people reported performance improvements when compiling the
> kernel without frame pointers.
>   
This solution is fine too (even if I still think that changing the 
default setting is better).

Please, consider the patch in attachment: is it like you would have it ?

BTW, do we have any list of buggy or not-EABI versions of the gcc compiler ?

Many thanks,

            Claudio


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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.

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


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