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

* 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.

Then the MAkefile fragment can be simplified as:
-obj-$(CONFIG_IMMEDIATE) += immediate.o
+obj-$(USE_IMMEDIATE) += immediate.o

(Or find a better name than "USE_IMMEDIATE".


endif

# Stackpointer is addressed different for 32 bit and 64 bit x86
Index: linux-2.6-sched-devel/include/asm-x86/immediate.h
===================================================================
--- linux-2.6-sched-devel.orig/include/asm-x86/immediate.h 2008-05-21 09:10:59.000000000 -0400
+++ linux-2.6-sched-devel/include/asm-x86/immediate.h 2008-05-21 09:15:43.000000000 -0400
@@ -12,6 +12,10 @@

#include <asm/asm.h>

+#if (defined(CONFIG_X86_64) && __GNUC__ < 4) /* Detect broken x86_64 gcc */
+#undef CONFIG_IMMEDIATE
+#else

And now in the source we use a direct check of the GNUC version. So this is a duplicate
of GCC_BROKEN_IMMEDIATE and not sensible comments.
"I ask myself in what way is gcc broken?"
And you DO NOT fiddle with the CONFIG_* variables - this is just plain wrong.


I could pass the USE_IMMEDIATE as a -D to the compiler flags. That would
be cleaner.

--- linux-2.6-sched-devel.orig/include/linux/immediate.h 2008-05-21 09:12:22.000000000 -0400
+++ linux-2.6-sched-devel/include/linux/immediate.h 2008-05-21 09:12:59.000000000 -0400
@@ -11,8 +11,10 @@
*/

#ifdef CONFIG_IMMEDIATE
+#include <asm/immediate.h> /* May undef CONFIG_IMMEDIATE */
+#endif

So you need to find a better way for this.


I think USE_IMMEDIATE is the way to go then.

Thanks,

Mathieu



-#include <asm/immediate.h>
+#ifdef CONFIG_IMMEDIATE

/**
* imv_set - set immediate variable (with locking)


--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

Relevant Pages

  • Re: [PATCH] Fix Immediate Values x86_64 support old gcc (v3)
    ... Fallback on generic immediate values if this compiler is ... +ifdef USE_IMMEDIATE ...
    (Linux-Kernel)
  • Re: RfD: Synonyms
    ... should IMMEDIATE be applied to a synonym that was already ... On some systems this can result in the synonym ... Compiling in COMPILER, compile HOST words and what to do with COMPILER ...
    (comp.lang.forth)
  • Re: RfD: Synonyms
    ... should IMMEDIATE be applied to a synonym that was already ... On some systems this can result in the synonym ... Compiling in COMPILER, compile HOST words and what to do with COMPILER ...
    (comp.lang.forth)
  • Re: [PATCH ftrace.git] Immedate Values Optimized Jump Fix
    ... e26875a: Immediate Values - Jump ... Immediate Values - x86 Optimization NMI and MCE support ... understood by the compiler, and I don't see how that could have been ...
    (Linux-Kernel)
  • Re: The IMMEDIATE mess (Andrew Haley)
    ... IMMEDIATE gives the only standard way to extend the compiler. ... want to get your work done and don't care about extending the compiler ...
    (comp.lang.forth)