[tip:x86/cleanups] x86: use kernel_stack_pointer() in kprobes.c

["tip-bot for H. Peter Anvin" <hpa@xxxxxxxxx>]

Commit-ID:  98272ed0d2e6509fe7dc571e77956c99bf653bb6
Gitweb:     http://git.kernel.org/tip/98272ed0d2e6509fe7dc571e77956c99bf653bb6
Author:     H. Peter Anvin <hpa@xxxxxxxxx>
AuthorDate: Mon, 12 Oct 2009 14:14:10 -0700
Committer:  H. Peter Anvin <hpa@xxxxxxxxx>
CommitDate: Mon, 12 Oct 2009 14:19:35 -0700

x86: use kernel_stack_pointer() in kprobes.c

The way to obtain a kernel-mode stack pointer from a struct pt_regs in
32-bit mode is "subtle": the stack doesn't actually contain the stack
pointer, but rather the location where it would have been marks the
actual previous stack frame.  For clarity, use kernel_stack_pointer()
instead of coding this weirdness explicitly.

Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Ananth N Mavinakayanahalli <ananth@xxxxxxxxxx>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@xxxxxxxxx>
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
---
 arch/x86/kernel/kprobes.c |   14 +-------------
 1 files changed, 1 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index 7b5169d..2ee4fa3 100644
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -60,19 +60,7 @@ void jprobe_return_end(void);
 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
 
-#ifdef CONFIG_X86_64
-#define stack_addr(regs) ((unsigned long *)regs->sp)
-#else
-/*
- * "&regs->sp" looks wrong, but it's correct for x86_32.  x86_32 CPUs
- * don't save the ss and esp registers if the CPU is already in kernel
- * mode when it traps.  So for kprobes, regs->sp and regs->ss are not
- * the [nonexistent] saved stack pointer and ss register, but rather
- * the top 8 bytes of the pre-int3 stack.  So &regs->sp happens to
- * point to the top of the pre-int3 stack.
- */
-#define stack_addr(regs) ((unsigned long *)&regs->sp)
-#endif
+#define stack_addr(regs) ((unsigned long *)kernel_stack_pointer(regs))
 
 #define W(row, b0, b1, b2, b3, b4, b5, b6, b7, b8, b9, ba, bb, bc, bd, be, bf)\
 	(((b0##UL << 0x0)|(b1##UL << 0x1)|(b2##UL << 0x2)|(b3##UL << 0x3) |   \
--
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