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    Subject[tip:x86/asm] x86, 64-bit: Use user_mode() to determine new stack pointer in copy_thread()
    Commit-ID:  fa4b8f84383ae197e643a46c36bf58ab8dffc95c
    Gitweb: http://git.kernel.org/tip/fa4b8f84383ae197e643a46c36bf58ab8dffc95c
    Author: Brian Gerst <brgerst@gmail.com>
    AuthorDate: Wed, 9 Dec 2009 12:34:41 -0500
    Committer: H. Peter Anvin <hpa@zytor.com>
    CommitDate: Thu, 10 Dec 2009 15:55:30 -0800

    x86, 64-bit: Use user_mode() to determine new stack pointer in copy_thread()

    Use user_mode() instead of a magic value for sp to determine when returning
    to kernel mode.

    Signed-off-by: Brian Gerst <brgerst@gmail.com>
    LKML-Reference: <1260380084-3707-3-git-send-email-brgerst@gmail.com>
    Signed-off-by: H. Peter Anvin <hpa@zytor.com>
    ---
    arch/x86/kernel/process_64.c | 7 ++++---
    1 files changed, 4 insertions(+), 3 deletions(-)

    diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
    index 92484c2..00ac66f 100644
    --- a/arch/x86/kernel/process_64.c
    +++ b/arch/x86/kernel/process_64.c
    @@ -254,7 +254,7 @@ int kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
    regs.flags = X86_EFLAGS_IF;

    /* Ok, create the new process.. */
    - return do_fork(flags | CLONE_VM | CLONE_UNTRACED, ~0UL, &regs, 0, NULL, NULL);
    + return do_fork(flags | CLONE_VM | CLONE_UNTRACED, 0, &regs, 0, NULL, NULL);
    }
    EXPORT_SYMBOL(kernel_thread);

    @@ -312,8 +312,9 @@ int copy_thread(unsigned long clone_flags, unsigned long sp,
    *childregs = *regs;

    childregs->ax = 0;
    - childregs->sp = sp;
    - if (sp == ~0UL)
    + if (user_mode(regs))
    + childregs->sp = sp;
    + else
    childregs->sp = (unsigned long)childregs;

    p->thread.sp = (unsigned long) childregs;

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