linux-kernel - Re: [patch 43/45] x86: replace LOCK

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Date:	Fri, 8 Feb 2008 19:35:33 +0100
From:	Stefan Lippers-Hollmann <s.L-H@....de>
To:	Greg KH <gregkh@...e.de>
Cc:	linux-kernel@...r.kernel.org, Chuck Ebbert <cebbert@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>, stable@...nel.org
Subject: Re: [patch 43/45] x86: replace LOCK_PREFIX in futex.h

Hi

On Donnerstag, 7. Februar 2008, Greg KH wrote:
> 2.6.24-stable review patch.  If anyone has any objections, please let us know.
> 
> ------------------
> From: Thomas Gleixner <tglx@...utronix.de>
> 
> The exception fixup for the futex macros __futex_atomic_op1/2 and
> futex_atomic_cmpxchg_inatomic() is missing an entry when the lock
> prefix is replaced by a NOP via SMP alternatives.
> 
> Chuck Ebert tracked this down from the information provided in:
> https://bugzilla.redhat.com/show_bug.cgi?id=429412
> 
> A possible solution would be to add another fixup after the
> LOCK_PREFIX, so both the LOCK and NOP case have their own entry in the
> exception table, but it's not really worth the trouble.
> 
> Simply replace LOCK_PREFIX with lock and keep those untouched by SMP
> alternatives.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
> 
> ---
>  include/asm-x86/futex_32.h |    6 +++---
>  include/asm-x86/futex_64.h |    6 +++---
>  2 files changed, 6 insertions(+), 6 deletions(-)

This patch seems to break compilation on x86_64 (i386 builds fine).

[...]
  CC      kernel/time/tick-sched.o
  LD      kernel/time/built-in.o
  CC      kernel/futex.o
In file included from include/asm/futex.h:4,
                 from kernel/futex.c:59:
include/asm/futex_64.h: In function ‘futex_atomic_op_inuser’:
include/asm/futex_64.h:69: error: expected ‘:’ or ‘)’ before ‘lock’
include/asm/futex_64.h:69: error: stray ‘\’ in program
In file included from include/asm/futex.h:4,
                 from kernel/futex.c:59:
include/asm/futex_64.h:69:61: error: invalid suffix "b" on integer constant
include/asm/futex_64.h:69: error: stray ‘\’ in program
include/asm/futex_64.h:69: error: stray ‘\’ in program
include/asm/futex_64.h:72: error: expected ‘:’ or ‘)’ before ‘lock’
include/asm/futex_64.h:72: error: stray ‘\’ in program
include/asm/futex_64.h:72:63: error: invalid suffix "b" on integer constant
include/asm/futex_64.h:72: error: stray ‘\’ in program
include/asm/futex_64.h:72: error: stray ‘\’ in program
include/asm/futex_64.h:75: error: expected ‘:’ or ‘)’ before ‘lock’
include/asm/futex_64.h:75: error: stray ‘\’ in program
include/asm/futex_64.h:75:62: error: invalid suffix "b" on integer constant
include/asm/futex_64.h:75: error: stray ‘\’ in program
include/asm/futex_64.h:75: error: stray ‘\’ in program
include/asm/futex_64.h:51: warning: unused variable ‘tem’
make[1]: *** [kernel/futex.o] Fehler 1
make: *** [kernel] Fehler 2

Tested on current debian-amd64/ unstable.
ii  binutils                                           2.18.1~cvs20080103-1       The GNU assembler, linker and binary utiliti
ii  gcc-4.2                                            4.2.3-1                    The GNU C compiler
ii  gcc-4.2-base                                       4.2.3-1                    The GNU Compiler Collection (base package)

[...]
> --- a/include/asm-x86/futex_64.h
> +++ b/include/asm-x86/futex_64.h
> @@ -27,7 +27,7 @@
>  "1:	movl	%2, %0\n\
>  	movl	%0, %3\n"					\
>  	insn "\n"						\
> -"2:	" LOCK_PREFIX "cmpxchgl %3, %2\n\
> +"2:	"lock cmpxchgl %3, %2\n\
>  	jnz	1b\n\
>  3:	.section .fixup,\"ax\"\n\
>  4:	mov	%5, %1\n\
> @@ -62,7 +62,7 @@ futex_atomic_op_inuser (int encoded_op, 
>  		__futex_atomic_op1("xchgl %0, %2", ret, oldval, uaddr, oparg);
>  		break;
>  	case FUTEX_OP_ADD:
> -		__futex_atomic_op1(LOCK_PREFIX "xaddl %0, %2", ret, oldval,
> +		__futex_atomic_op1("lock xaddl %0, %2", ret, oldval,
>  				   uaddr, oparg);
>  		break;
>  	case FUTEX_OP_OR:
> @@ -101,7 +101,7 @@ futex_atomic_cmpxchg_inatomic(int __user
>  		return -EFAULT;
>  
>  	__asm__ __volatile__(
> -		"1:	" LOCK_PREFIX "cmpxchgl %3, %1		\n"
> +		"1:	lock cmpxchgl %3, %1			\n"
>  
>  		"2:	.section .fixup, \"ax\"			\n"
>  		"3:	mov     %2, %0				\n"

Regards
	Stefan Lippers-Hollmann

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