Re: [PATCH 1/3] x86: Create and use a TOP_OF_KERNEL_STACK_PADDING macro

[Denys Vlasenko <vda.linux@googlemail.com>]

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.