[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>

diff --git a/arch/i386/kernel/process.c b/arch/i386/kernel/process.c
index 5dd0375..3d7e0c8 100644 (file)
--- 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 a9bf5f2..255adb4 100644 (file)
--- 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;
        }

diff --git a/include/asm-i386/processor.h b/include/asm-i386/processor.h
index 13ecf66..29ad87e 100644 (file)
--- a/include/asm-i386/processor.h
+++ b/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;                                                   \
 })