Message-ID: <4AE55D83.7080608@evidence.eu.com>
Date: Mon, 26 Oct 2009 09:27:47 +0100
From: Claudio Scordino <claudio@evidence.eu.com>
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To: linux-kernel@vger.kernel.org
CC: Catalin Marinas <catalin.marinas@arm.com>, rmk+kernel@arm.linux.org.uk,
       linux-arm-kernel@lists.arm.linux.org.uk, akpm@linux-foundation.org
Subject: [PATCH][RE-SUBMIT] Default setting of the ARM_UNWIND option
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Hi all,

          I didn't get any comment on this patch, so I try to re-submit.

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).

Having this option enabled by default, in fact, means that the kernel
does not boot if the user has a wrong compiler. If so, inspecting the
reason of the hang may require too much time (especially for people not
familiar with this option).

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

If we disable this option by default, users who know the real meaning of
the option will still be able of setting it to the proper value.

Any comment ?

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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