[PATCH] x86: compress the stack layout of do_page_fault()

This patch pushes the creation of a rare signal frame (SIGBUS or SIGSEGV)
into a separate function, thus saving stackspace in the main
do_page_fault() stackframe.  The effect is 132 bytes less of stack used by
the typical do_page_fault() invocation - resulting in a denser
cache-layout.

(Another minor effect is that in case of kernel crashes that come from a
pagefault, we add less space to the already existing frame, giving the
crash functions a slightly higher chance to do their stuff without
overflowing the stack.)

(The changes also result in slightly cleaner code.)

argument bugfix from "Guillaume C." <guichaz@gmail.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

arch/i386/mm/fault.c

@@ -199,6 +199,18 @@ static inline int is_prefetch(struct pt_regs *regs, unsigned long addr,
 	return 0;
 } 
 
+static noinline void force_sig_info_fault(int si_signo, int si_code,
+	unsigned long address, struct task_struct *tsk)
+{
+	siginfo_t info;
+
+	info.si_signo = si_signo;
+	info.si_errno = 0;
+	info.si_code = si_code;
+	info.si_addr = (void __user *)address;
+	force_sig_info(si_signo, &info, tsk);
+}
+
 fastcall void do_invalid_op(struct pt_regs *, unsigned long);
 
 /*
@@ -218,8 +230,7 @@ fastcall void do_page_fault(struct pt_regs *regs, unsigned long error_code)
 	struct vm_area_struct * vma;
 	unsigned long address;
 	unsigned long page;
-	int write;
-	siginfo_t info;
+	int write, si_code;
 
 	/* get the address */
 	__asm__("movl %%cr2,%0":"=r" (address));
@@ -233,7 +244,7 @@ fastcall void do_page_fault(struct pt_regs *regs, unsigned long error_code)
 
 	tsk = current;
 
-	info.si_code = SEGV_MAPERR;
+	si_code = SEGV_MAPERR;
 
 	/*
 	 * We fault-in kernel-space virtual memory on-demand. The
@@ -313,7 +324,7 @@ fastcall void do_page_fault(struct pt_regs *regs, unsigned long error_code)
  * we can handle it..
  */
 good_area:
-	info.si_code = SEGV_ACCERR;
+	si_code = SEGV_ACCERR;
 	write = 0;
 	switch (error_code & 3) {
 		default:	/* 3: write, present */
@@ -387,11 +398,7 @@ fastcall void do_page_fault(struct pt_regs *regs, unsigned long error_code)
 		/* Kernel addresses are always protection faults */
 		tsk->thread.error_code = error_code | (address >= TASK_SIZE);
 		tsk->thread.trap_no = 14;
-		info.si_signo = SIGSEGV;
-		info.si_errno = 0;
-		/* info.si_code has been set above */
-		info.si_addr = (void __user *)address;
-		force_sig_info(SIGSEGV, &info, tsk);
+		force_sig_info_fault(SIGSEGV, si_code, address, tsk);
 		return;
 	}
 
@@ -500,11 +507,7 @@ fastcall void do_page_fault(struct pt_regs *regs, unsigned long error_code)
 	tsk->thread.cr2 = address;
 	tsk->thread.error_code = error_code;
 	tsk->thread.trap_no = 14;
-	info.si_signo = SIGBUS;
-	info.si_errno = 0;
-	info.si_code = BUS_ADRERR;
-	info.si_addr = (void __user *)address;
-	force_sig_info(SIGBUS, &info, tsk);
+	force_sig_info_fault(SIGBUS, BUS_ADRERR, address, tsk);
 	return;
 
 vmalloc_fault: