Re: [PATCH] Fix Immediate Values x86_64 support old gcc

On Wed, May 21, 2008 at 05:28:09PM -0400, Mathieu Desnoyers wrote:
* Sam Ravnborg (sam@xxxxxxxxxxxx) wrote:
Hi Mathieu
Does this fix make more sense ?

GCC < 4, on x86_64, does not accept symbol+offset operands for "i" constraints
asm statements. Fallback on generic immediate values if this compiler is
detected.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
---
arch/x86/Makefile | 3 +++
arch/x86/kernel/Makefile | 4 +++-
include/asm-x86/immediate.h | 5 +++++
include/linux/immediate.h | 4 +++-
kernel/Makefile | 4 +++-
5 files changed, 17 insertions(+), 3 deletions(-)

Index: linux-2.6-sched-devel/arch/x86/Makefile
===================================================================
--- linux-2.6-sched-devel.orig/arch/x86/Makefile 2008-05-21 09:04:52.000000000 -0400
+++ linux-2.6-sched-devel/arch/x86/Makefile 2008-05-21 09:22:05.000000000 -0400
@@ -78,6 +78,9 @@
"$(CC)" -fstack-protector-all )

KBUILD_CFLAGS += $(stackp-y)
+
+ export GCC_BROKEN_IMMEDIATE
+ GCC_BROKEN_IMMEDIATE := $(shell if [ $(call cc-version) -lt 0400 ] ; then echo "y"; fi)

So here we introduce a global environment variable that tells
us that gcc has "BROKEN_IMMEDIATE".
I have absolutely no clue what "BROKEN_IMMEDIATE" is so I guess others
are in the same boat. Comment please!


Yes, I guess this worth being commented, you are right. I'll write
something along the lines written in the patch header.

Consider something like this (note: no negative logic involved):
export USE_IMMEDIATE := $(call cc-ifversion, -ge, 0400, $(CONFIG_IMMEDIATE))


Hrm, if I do that, I would have to add USE_IMMEDIATE to each
architecture's makefiles for which immediate values are supported, e.g.:

export USE_IMMEDIATE := $(CONFIG_IMMEDIATE)

The "BROKEN_IMMEDIATE" (negative) approach only needs to be defined on
x86_64 where gcc 3.x does not support symbol+offset correctly.
Same with USE_IMMEDIATE - as USE_IMMEDIATE is only used in a x86 Makefile.
Or did I miss sothing?

Sam
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