[PATCH] i386: fix task_pt_regs()

)

From: Al Viro <viro@ftp.linux.org.uk>

task_pt_regs() needs the same offset-by-8 to match copy_thread()
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

arch/i386/kernel/process.c

@@ -424,18 +424,7 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long esp,
 	struct task_struct *tsk;
 	int err;
 
-	childregs = ((struct pt_regs *) (THREAD_SIZE + (unsigned long) p->thread_info)) - 1;
-	/*
-	 * The below -8 is to reserve 8 bytes on top of the ring0 stack.
-	 * This is necessary to guarantee that the entire "struct pt_regs"
-	 * is accessable even if the CPU haven't stored the SS/ESP registers
-	 * on the stack (interrupt gate does not save these registers
-	 * when switching to the same priv ring).
-	 * Therefore beware: accessing the xss/esp fields of the
-	 * "struct pt_regs" is possible, but they may contain the
-	 * completely wrong values.
-	 */
-	childregs = (struct pt_regs *) ((unsigned long) childregs - 8);
+	childregs = task_pt_regs(p);
 	*childregs = *regs;
 	childregs->eax = 0;
 	childregs->esp = esp;
@@ -540,12 +529,7 @@ EXPORT_SYMBOL(dump_thread);
  */
 int dump_task_regs(struct task_struct *tsk, elf_gregset_t *regs)
 {
-	struct pt_regs ptregs;
-	
-	ptregs = *(struct pt_regs *)
-		((unsigned long)tsk->thread_info +
-		/* see comments in copy_thread() about -8 */
-		THREAD_SIZE - sizeof(ptregs) - 8);
+	struct pt_regs ptregs = *task_pt_regs(tsk);
 	ptregs.xcs &= 0xffff;
 	ptregs.xds &= 0xffff;
 	ptregs.xes &= 0xffff;

arch/i386/kernel/smpboot.c

@@ -875,8 +875,7 @@ static inline struct task_struct * alloc_idle_task(int cpu)
 		/* initialize thread_struct.  we really want to avoid destroy
 		 * idle tread
 		 */
-		idle->thread.esp = (unsigned long)(((struct pt_regs *)
-			(THREAD_SIZE + (unsigned long) idle->thread_info)) - 1);
+		idle->thread.esp = (unsigned long)task_pt_regs(idle);
 		init_idle(idle, cpu);
 		return idle;
 	}

include/asm-i386/processor.h

@@ -561,10 +561,20 @@ unsigned long get_wchan(struct task_struct *p);
        (unsigned long)(&__ptr[THREAD_SIZE_LONGS]);                     \
 })
 
+/*
+ * The below -8 is to reserve 8 bytes on top of the ring0 stack.
+ * This is necessary to guarantee that the entire "struct pt_regs"
+ * is accessable even if the CPU haven't stored the SS/ESP registers
+ * on the stack (interrupt gate does not save these registers
+ * when switching to the same priv ring).
+ * Therefore beware: accessing the xss/esp fields of the
+ * "struct pt_regs" is possible, but they may contain the
+ * completely wrong values.
+ */
 #define task_pt_regs(task)                                             \
 ({                                                                     \
        struct pt_regs *__regs__;                                       \
-       __regs__ = (struct pt_regs *)KSTK_TOP((task)->thread_info);     \
+       __regs__ = (struct pt_regs *)(KSTK_TOP((task)->thread_info)-8); \
        __regs__ - 1;                                                   \
 })