linux-kernel - Re: vread_tsc() compile error (post 2.6.26)

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Date:	Tue, 15 Jul 2008 22:11:02 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
cc:	mingo <mingo@...e.hu>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Alok N Kataria <akataria@...are.com>,
	Alok N Kataria <akataria@...are.com>,
	Dan Hecht <dhecht@...are.com>
Subject: Re: vread_tsc() compile error (post 2.6.26)

On Tue, 15 Jul 2008, Dave Hansen wrote:
> $ git describe
> v2.6.26-2465-g1c0fea9
> 
> This looks like it was caused by:
> 
> 	8fbbc4b45ce3e4c0eeb15004c79c72b6896a79c2
> 
> Did this get any testing on x86-32?  It looks like this symbol has no
> 32-bit equivalent.

Doh, that's odd. It compiles, links and boots here. Looks like the my gcc just
optimizes it out without the usual "...., but not used warning"

Patch below.

Thanks,

	tglx

> ...
>   MODPOST vmlinux.o
> WARNING: modpost: Found 11 section mismatch(es).
> To see full details build your kernel with:
> 'make CONFIG_DEBUG_SECTION_MISMATCH=y'
>   GEN     .version
>   CHK     include/linux/compile.h
>   UPD     include/linux/compile.h
>   CC      init/version.o
>   LD      init/built-in.o
>   LD      .tmp_vmlinux1
> arch/x86/kernel/built-in.o: In function `vread_tsc':
> /home/dave/kernels/linux-2.6.git/arch/x86/kernel/tsc.c:365: undefined reference to `__vsyscall_gtod_data'
> /home/dave/kernels/linux-2.6.git/arch/x86/kernel/tsc.c:365: undefined reference to `__vsyscall_gtod_data'
> make: *** [.tmp_vmlinux1] Error 1
> 
> My config:
> 
> http://sr71.net/~dave/linux/config-2.6.26-rc8-00089-ge1441b9

----------------->

Subject: x86: fix tsc unification fallout
From: Thomas Gleixner <tglx@...utronix.de>
Date: Tue, 15 Jul 2008 22:08:04 +0200

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 arch/x86/kernel/tsc.c |    2 ++
 1 file changed, 2 insertions(+)

Index: linux-2.6/arch/x86/kernel/tsc.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/tsc.c
+++ linux-2.6/arch/x86/kernel/tsc.c
@@ -358,6 +358,7 @@ static cycle_t read_tsc(void)
 		ret : clocksource_tsc.cycle_last;
 }
 
+#ifdef CONFIG_X86_64
 static cycle_t __vsyscall_fn vread_tsc(void)
 {
 	cycle_t ret = (cycle_t)vget_cycles();
@@ -365,6 +366,7 @@ static cycle_t __vsyscall_fn vread_tsc(v
 	return ret >= __vsyscall_gtod_data.clock.cycle_last ?
 		ret : __vsyscall_gtod_data.clock.cycle_last;
 }
+#endif
 
 static struct clocksource clocksource_tsc = {
 	.name                   = "tsc",