x86, ptrace: fix build breakage with gcc 4.7

Christoph Biedl reported that 2.6.32 does not build with gcc 4.7 on
i386 :

  CC      arch/x86/kernel/ptrace.o
arch/x86/kernel/ptrace.c:1472:17: error: conflicting types for 'syscall_trace_enter'
In file included from /«PKGBUILDDIR»/arch/x86/include/asm/vm86.h:130:0,
                 from /«PKGBUILDDIR»/arch/x86/include/asm/processor.h:10,
                 from /«PKGBUILDDIR»/arch/x86/include/asm/thread_info.h:22,
                 from include/linux/thread_info.h:56,
                 from include/linux/preempt.h:9,
                 from include/linux/spinlock.h:50,
                 from include/linux/seqlock.h:29,
                 from include/linux/time.h:8,
                 from include/linux/timex.h:56,
                 from include/linux/sched.h:56,
                 from arch/x86/kernel/ptrace.c:11:
/«PKGBUILDDIR»/arch/x86/include/asm/ptrace.h:145:13: note: previous declaration of 'syscall_trace_enter' was here
arch/x86/kernel/ptrace.c:1517:17: error: conflicting types for 'syscall_trace_leave'
In file included from /«PKGBUILDDIR»/arch/x86/include/asm/vm86.h:130:0,
                 from /«PKGBUILDDIR»/arch/x86/include/asm/processor.h:10,
                 from /«PKGBUILDDIR»/arch/x86/include/asm/thread_info.h:22,
                 from include/linux/thread_info.h:56,
                 from include/linux/preempt.h:9,
                 from include/linux/spinlock.h:50,
                 from include/linux/seqlock.h:29,
                 from include/linux/time.h:8,
                 from include/linux/timex.h:56,
                 from include/linux/sched.h:56,
                 from arch/x86/kernel/ptrace.c:11:
/«PKGBUILDDIR»/arch/x86/include/asm/ptrace.h:146:13: note: previous declaration of 'syscall_trace_leave' was here
make[4]: *** [arch/x86/kernel/ptrace.o] Error 1
make[3]: *** [arch/x86/kernel] Error 2
make[3]: *** Waiting for unfinished jobs....

He also found that this issue did not appear in more recent kernels since
this asmregparm disappeared in 3.0-rc1 with commit 1b4ac2a that was
applied after some UM changes that we don't necessarily want in 2.6.32.

Thus, the cleanest fix for older kernels is to make the declaration in
ptrace.h match the one in ptrace.c by specifying asmregparm on these
functions. They're only called from asm which explains why it used to
work despite the inconsistency in the declaration.

Reported-by: Christoph Biedl <linux-kernel.bfrz@manchmal.in-ulm.de>
Tested-by: Christoph Biedl <linux-kernel.bfrz@manchmal.in-ulm.de>
Signed-off-by: Willy Tarreau <w@1wt.eu>

arch/x86/include/asm/ptrace.h

@@ -2,6 +2,7 @@
 #define _ASM_X86_PTRACE_H
 
 #include <linux/compiler.h>	/* For __user */
+#include <linux/linkage.h>	/* For asmregparm */
 #include <asm/ptrace-abi.h>
 #include <asm/processor-flags.h>
 
@@ -142,8 +143,8 @@ extern void send_sigtrap(struct task_struct *tsk, struct pt_regs *regs,
 			 int error_code, int si_code);
 void signal_fault(struct pt_regs *regs, void __user *frame, char *where);
 
-extern long syscall_trace_enter(struct pt_regs *);
-extern void syscall_trace_leave(struct pt_regs *);
+extern asmregparm long syscall_trace_enter(struct pt_regs *);
+extern asmregparm void syscall_trace_leave(struct pt_regs *);
 
 static inline unsigned long regs_return_value(struct pt_regs *regs)
 {