Merge branch 'kbuild' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild

[cascardo/linux.git] / arch / x86 / entry / entry_32.S

diff --git a/arch/x86/entry/entry_32.S b/arch/x86/entry/entry_32.S
index 64d29a3..21b352a 100644 (file)
--- a/arch/x86/entry/entry_32.S
+++ b/arch/x86/entry/entry_32.S
@@ -205,34 +205,70 @@
        POP_GS_EX
 .endm
 
+/*
+ * %eax: prev task
+ * %edx: next task
+ */
+ENTRY(__switch_to_asm)
+       /*
+        * Save callee-saved registers
+        * This must match the order in struct inactive_task_frame
+        */
+       pushl   %ebp
+       pushl   %ebx
+       pushl   %edi
+       pushl   %esi
+
+       /* switch stack */
+       movl    %esp, TASK_threadsp(%eax)
+       movl    TASK_threadsp(%edx), %esp
+
+#ifdef CONFIG_CC_STACKPROTECTOR
+       movl    TASK_stack_canary(%edx), %ebx
+       movl    %ebx, PER_CPU_VAR(stack_canary)+stack_canary_offset
+#endif
+
+       /* restore callee-saved registers */
+       popl    %esi
+       popl    %edi
+       popl    %ebx
+       popl    %ebp
+
+       jmp     __switch_to
+END(__switch_to_asm)
+
+/*
+ * A newly forked process directly context switches into this address.
+ *
+ * eax: prev task we switched from
+ * ebx: kernel thread func (NULL for user thread)
+ * edi: kernel thread arg
+ */
 ENTRY(ret_from_fork)
        pushl   %eax
        call    schedule_tail
        popl    %eax
 
+       testl   %ebx, %ebx
+       jnz     1f              /* kernel threads are uncommon */
+
+2:
        /* When we fork, we trace the syscall return in the child, too. */
        movl    %esp, %eax
        call    syscall_return_slowpath
        jmp     restore_all
-END(ret_from_fork)
-
-ENTRY(ret_from_kernel_thread)
-       pushl   %eax
-       call    schedule_tail
-       popl    %eax
-       movl    PT_EBP(%esp), %eax
-       call    *PT_EBX(%esp)
-       movl    $0, PT_EAX(%esp)
 
+       /* kernel thread */
+1:     movl    %edi, %eax
+       call    *%ebx
        /*
-        * Kernel threads return to userspace as if returning from a syscall.
-        * We should check whether anything actually uses this path and, if so,
-        * consider switching it over to ret_from_fork.
+        * A kernel thread is allowed to return here after successfully
+        * calling do_execve().  Exit to userspace to complete the execve()
+        * syscall.
         */
-       movl    %esp, %eax
-       call    syscall_return_slowpath
-       jmp     restore_all
-ENDPROC(ret_from_kernel_thread)
+       movl    $0, PT_EAX(%esp)
+       jmp     2b
+END(ret_from_fork)
 
 /*
  * Return to user mode is not as complex as all this looks,