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    SubjectRe: [PATCH 1/3] x86: Create and use a TOP_OF_KERNEL_STACK_PADDING macro
    On Tue, Mar 10, 2015 at 8:22 PM, Denys Vlasenko <dvlasenk@redhat.com> wrote:
    > On 03/10/2015 07:05 PM, Andy Lutomirski wrote:
    >> x86_32, unlike x86_64, pads the top of the kernel stack. Document
    >> this padding and give it a name.
    >>
    >> This should make no change whatsoever to the compiled kernel image.
    >> It also doesn't fix any of the current bugs in this area.
    >>
    >> Signed-off-by: Andy Lutomirski <luto@amacapital.net>
    >> ---
    >> arch/x86/include/asm/processor.h | 3 ++-
    >> arch/x86/include/asm/thread_info.h | 30 ++++++++++++++++++++++++++++++
    >> 2 files changed, 32 insertions(+), 1 deletion(-)
    >>
    >> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
    >> index 48a61c1c626e..88d9aa745898 100644
    >> --- a/arch/x86/include/asm/processor.h
    >> +++ b/arch/x86/include/asm/processor.h
    >> @@ -849,7 +849,8 @@ extern unsigned long thread_saved_pc(struct task_struct *tsk);
    >> #define task_pt_regs(task) \
    >> ({ \
    >> struct pt_regs *__regs__; \
    >> - __regs__ = (struct pt_regs *)(KSTK_TOP(task_stack_page(task))-8); \
    >> + __regs__ = (struct pt_regs *)(KSTK_TOP(task_stack_page(task)) - \
    >> + TOP_OF_KERNEL_STACK_PADDING); \
    >> __regs__ - 1; \
    >> })

    While we are at it, this macro can be simplified further. It uses KSTK_TOP,
    and it's the only use of that macro. In turn, KSTK_TOP uses THREAD_SIZE_LONGS,
    and it is the only use of that macro too!
    (And to nitpick, this macro is whitespace-damaged. Seven space indent).

    I'll send a patch based on your current git.


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