[U-Boot] [RFC PATCH 2/4] OMAP3+: fix issues with Thumb build

[Aneesh V]

Hi Albert,

On Tuesday 07 February 2012 02:36 AM, Albert ARIBAUD wrote:
> Le 06/02/2012 12:37, Aneesh V a écrit :
>> When U-Boot/SPL is built using the Thumb instruction set the
>> toolchain has a potential issue with weakly linked symbols.
>> If a function has a weakly linked default implementation in C
>> and a real implementation in assembly GCC is confused about the
>> instruction set of the assembly implementation. As a result
>> the assembly function that is built in ARM is executed as
>> if it is Thumb. This results in a crash.
>>
>> We need to investigate further to see if this is a toolchain
>> issue or an issue with our usage of it. In the meanwhile, we
>> can workaround the issue by having both the weakly linked alias
>> and the real implementation in C.
>
> I would tend to NAK a patch submission where an issue is known and
> investigation is considered but is actually bypassed by a workaround.
> These tend to turn from 'temporary fix' to 'old crust' with time,
> because there is no incentive for a better solution when the quick fix
> "works, after all".

I have a solution to this problem now. The following change solves it.

diff --git a/arch/arm/cpu/armv7/omap-common/lowlevel_init.S 
b/arch/arm/cpu/armv7/omap-common/lowlevel_init.S
index 35f38ac..177af7a 100644
--- a/arch/arm/cpu/armv7/omap-common/lowlevel_init.S
+++ b/arch/arm/cpu/armv7/omap-common/lowlevel_init.S
@@ -28,6 +28,7 @@

  #include <asm/arch/omap.h>

+.type   save_boot_params, %function
  .global save_boot_params
  save_boot_params:
  	/*

Apparently having the symbol marked as %function type in the symbol
table helps ld. However, not having the %function tag doesn't prevent
ld from linking correctly to this function. It affects only ARM/Thumb
resolution. Strange!

I came to this solution from the test-code provided by Ulrich Weigand
in reply to my queries in Linaro ML [1]. I couldn't reproduce the
problem with his code, but eventually could break it when I removed
the %function.

I will continue this discussion there and to understand whether this is
a limitation with GCC.

However, hope you are fine with the above solution. I shall fix up all
assembly functions in arm.

[1] http://article.gmane.org/gmane.linux.linaro.devel/3073

br,
Aneesh