[U-Boot] [PATCH v2 2/2] arm: work around assembler bug

[Tom Rini]

On Tue, Jul 10, 2012 at 10:00:17AM -0700, Allen Martin wrote:
> Disable sibling call optimization based on binutils version.  This is
> to work around a bug in the assember in binutils versions < 2.22.
> Branches to weak symbols can be incorrectly optimized in thumb mode to
> a short branch (b.n instruction) that won't reach when the symbol gets
> preempted.
> 
> http://sourceware.org/bugzilla/show_bug.cgi?id=12532
> 
> Signed-off-by: Allen Martin <amartin at nvidia.com>
> ---
> changes for v2:
>  -changed GAS_BUG_12532 from yes/no to y/n to be consistent
>  -added additional warning about code size increase
> ---
>  arch/arm/config.mk |   21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/arch/arm/config.mk b/arch/arm/config.mk
> index 3f4453a..bcabf17 100644
> --- a/arch/arm/config.mk
> +++ b/arch/arm/config.mk
> @@ -87,3 +87,24 @@ endif
>  ifndef CONFIG_NAND_SPL
>  LDFLAGS_u-boot += -pie
>  endif
> +
> +#
> +# binutils versions < 2.22 have a bug in the assembler where branches
> +# to weak symbols can be incorrectly optimized in thumb mode to a
> +# short branch (b.n instruction) that won't reach when the symbol
> +# gets preempted
> +#
> +# http://sourceware.org/bugzilla/show_bug.cgi?id=12532
> +#
> +ifeq ($(CONFIG_SYS_THUMB_BUILD),y)
> +ifeq ($(GAS_BUG_12532),)
> +export GAS_BUG_12532:=$(shell if [ $(call binutils-version) -lt 0222 ] ; then echo y; else echo n; fi)

Please don't squash out whitespace, just break this out into a
multi-line test ala the others in the toplevel config.mk.

> +ifeq ($(GAS_BUG_12532),y)
> +$(warning *** disabling sibling call optimzation because binutils version < 2.22)
> +$(warning *** code size may be slightly larger)
> +endif
> +endif
> +ifeq ($(GAS_BUG_12532),y)
> +PLATFORM_RELFLAGS += -fno-optimize-sibling-calls
> +endif
> +endif

This seems a bit longer than needed.  Just check that it's y once and do
both things.  Also, I _think_ we should be able to squish this down to:
ifeq ($(CONFIG_SYS_THUMB_BUILD),y)
GAS_BUG_12532 := $(shell if [ $(call binutils-version) -lt 0222 ] ; \
	then echo y; else echo n; fi)
ifeq ($(GAS_BUG_125320),y)
$(warning ...)
$(warning ...)
PLATFORM_RELFLAGS += ...
endif
endif

But I haven't tested it.

-- 
Tom
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