[PATCH] i386: fix task_pt_regs()

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

task_pt_regs() needs the same offset-by-8 to match copy_thread()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 3 insertions, 20 deletions

diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c
index 5dd03757f50c..3d7e0c8e9925 100644
--- a/arch/i386/kernel/process.c
+++ b/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;
diff --git a/arch/i386/kernel/smpboot.c b/arch/i386/kernel/smpboot.c
index a9bf5f222e47..255adb498268 100644
--- a/arch/i386/kernel/smpboot.c
+++ b/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;
         }