[PATCH] kprobes: dont steal interrupts from vm86

The address used by the kprobes handler was not correct if the application
was using LDT entries for code segment.  This patch fixes the above problem
by calculating the address using base address of the current code segment. 
Also this patch removes the inline prefix of kprobe_handler() .
Signed-off-by: Prasanna S Panchamukhi <prasanna@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/i386/kernel/kprobes.c

@@ -86,15 +86,28 @@ static inline void prepare_singlestep(struct kprobe *p, struct pt_regs *regs)
  * Interrupts are disabled on entry as trap3 is an interrupt gate and they
  * remain disabled thorough out this function.
  */
-static inline int kprobe_handler(struct pt_regs *regs)
+static int kprobe_handler(struct pt_regs *regs)
 {
 	struct kprobe *p;
 	int ret = 0;
-	u8 *addr = (u8 *) (regs->eip - 1);
+	kprobe_opcode_t *addr = NULL;
+	unsigned long *lp;
 
 	/* We're in an interrupt, but this is clear and BUG()-safe. */
 	preempt_disable();
-
+	/* Check if the application is using LDT entry for its code segment and
+	 * calculate the address by reading the base address from the LDT entry.
+	 */
+	if ((regs->xcs & 4) && (current->mm)) {
+		lp = (unsigned long *) ((unsigned long)((regs->xcs >> 3) * 8)
+					+ (char *) current->mm->context.ldt);
+		addr = (kprobe_opcode_t *) ((((*lp) >> 16 &  0x0000ffff)
+				| (*(lp +1) & 0xff000000)
+				| ((*(lp +1) << 16) & 0x00ff0000))
+				+ regs->eip - sizeof(kprobe_opcode_t));
+	} else {
+		addr = (kprobe_opcode_t *)(regs->eip - sizeof(kprobe_opcode_t));
+	}
 	/* Check we're not actually recursing */
 	if (kprobe_running()) {
 		/* We *are* holding lock here, so this is safe.