From: Chuck Ebbert <76306.1226@compuserve.com>

Fix and clean up kretprobe-kretprobe-booster by:

        - Not reserving 8 bytes at stack bottom
        - Making trampoline_handler fastcall and calling it directly
        - Using "iret" to return to original caller

Using "iret" is slightly slower than direct return; time went from 1030 CPU
cycles overhead per kretprobe to 1050 cycles (2%), but the code is cleaner.

Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>
Cc: Masami Hiramatsu <hiramatu@sdl.hitachi.co.jp>
Cc: Prasanna S Panchamukhi <prasanna@in.ibm.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 arch/i386/kernel/kprobes.c |   24 ++++++++++--------------
 1 files changed, 10 insertions(+), 14 deletions(-)

diff -puN arch/i386/kernel/kprobes.c~kretprobe-kretprobe-booster-fixes arch/i386/kernel/kprobes.c
--- 25/arch/i386/kernel/kprobes.c~kretprobe-kretprobe-booster-fixes	Tue Feb  7 16:00:36 2006
+++ 25-akpm/arch/i386/kernel/kprobes.c	Tue Feb  7 16:00:36 2006
@@ -325,9 +325,10 @@ no_kprobe:
  {
 	 asm volatile ( ".global kretprobe_trampoline\n"
  			"kretprobe_trampoline: \n"
-			"	subl $8, %esp\n"
 			"	pushf\n"
-			"	subl $20, %esp\n"
+			"	pushl %cs\n"
+			/* skip eip, orig_eax, es, ds */
+			"	subl $16, %esp\n"
 			"	pushl %eax\n"
 			"	pushl %ebp\n"
 			"	pushl %edi\n"
@@ -336,13 +337,9 @@ no_kprobe:
 			"	pushl %ecx\n"
 			"	pushl %ebx\n"
 			"	movl %esp, %eax\n"
-			"	pushl %eax\n"
-			"	addl $60, %eax\n"
-			"	movl %eax, 56(%esp)\n"
-			"	movl $trampoline_handler, %eax\n"
-			"	call *%eax\n"
-			"	addl $4, %esp\n"
-			"	movl %eax, 56(%esp)\n"
+			"	call trampoline_handler\n"
+			/* save new eip */
+			"	movl %eax, 40(%esp)\n"
 			"	popl %ebx\n"
 			"	popl %ecx\n"
 			"	popl %edx\n"
@@ -350,16 +347,15 @@ no_kprobe:
 			"	popl %edi\n"
 			"	popl %ebp\n"
 			"	popl %eax\n"
-			"	addl $20, %esp\n"
-			"	popf\n"
-			"	addl $4, %esp\n"
-			"	ret\n");
+			/* skip ds, es, orig_eax */
+			"	addl $12, %esp\n"
+			"	iret\n");
 }
 
 /*
  * Called from kretprobe_trampoline
  */
-asmlinkage void *__kprobes trampoline_handler(struct pt_regs *regs)
+fastcall void *__kprobes trampoline_handler(struct pt_regs *regs)
 {
         struct kretprobe_instance *ri = NULL;
         struct hlist_head *head;
_