From mboxrd@z Thu Jan  1 00:00:00 1970
From: will.deacon@arm.com (Will Deacon)
Date: Thu, 2 Aug 2012 16:01:23 +0100
Subject: [PATCH] ARM: makefile: work around toolchain bug in recent
 versions of binutils
In-Reply-To: <20120802130411.GU6802@n2100.arm.linux.org.uk>
References: <1343910206-3684-1-git-send-email-will.deacon@arm.com>
 <20120802130411.GU6802@n2100.arm.linux.org.uk>
Message-ID: <20120802150123.GE9838@mudshark.cambridge.arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

Hi Russell,

On Thu, Aug 02, 2012 at 02:04:11PM +0100, Russell King - ARM Linux wrote:
> On Thu, Aug 02, 2012 at 01:23:26PM +0100, Will Deacon wrote:
> > Recent upstream versions of binutils fail to assembler compressed/head.S
> > when passed the -march=all option:
> > 
> > http://lists.gnu.org/archive/html/bug-binutils/2011-04/msg00162.html
> > 
> > The recommended workaround from the tools folks is not to pass the
> > option, and instead let the assembler deduce the CPU type based on the
> > features used by the code.
> 
> That doesn't work for all binutils - binutils historically has had to be
> told explicitly what architecture its building for and won't "deduce"
> it from the code.

Damn. I thought there would be a reason why we passed the option in the
first place.

> Maybe this needs to be a build-time test whether the assembler accepts it?

That could be tricky since gas still accepts the option, but fails later
with:

arch/arm/boot/compressed/head.S: Assembler messages:
arch/arm/boot/compressed/head.S:127: Error: selected processor does not support requested special purpose register -- `mrs r2,cpsr'
arch/arm/boot/compressed/head.S:134: Error: selected processor does not support requested special purpose register -- `mrs r2,cpsr'
arch/arm/boot/compressed/head.S:136: Error: selected processor does not support requested special purpose register -- `msr cpsr_c,r2'

How about grabbing the march from KBUILD_AFLAGS instead (see below)?

Will

---8<---

diff --git a/arch/arm/boot/compressed/Makefile b/arch/arm/boot/compressed/Makefile
index bb26756..3774f0d 100644
--- a/arch/arm/boot/compressed/Makefile
+++ b/arch/arm/boot/compressed/Makefile
@@ -126,7 +126,7 @@ KBUILD_CFLAGS = $(subst -pg, , $(ORIG_CFLAGS))
 endif
 
 ccflags-y := -fpic -fno-builtin -I$(obj)
-asflags-y := -Wa,-march=all
+asflags-y := -Wa,$(lastword $(filter -march=%,$(KBUILD_AFLAGS)))
 
 # Supply kernel BSS size to the decompressor via a linker symbol.
 KBSS_SZ = $(shell $(CROSS_COMPILE)size $(obj)/../../../../vmlinux | \