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SubjectRe: [PATCH -rc] [BUGFIX] x86: fix kernel_trap_sp()
Robin Holt wrote:
> On Mon, May 11, 2009 at 03:24:07PM -0700, Linus Torvalds wrote:
>>
>> On Mon, 11 May 2009, Masami Hiramatsu wrote:
>>> Use &regs->sp instead of regs for getting the top of stack in kernel mode.
>>> (on x86-64, regs->sp always points the top of stack)
>> Ack.
>>
>> That said, we have only _one_ use of this "kernel_trap_sp()" in the whole
>> kernel, and that use is actually fairly odd too, in that it does it
>> _before_ checking that it's in kernel mode.
>>
>> Admittedly it will then only _use_ the value after it has checked that
>> things are in kernel mode, but it all boils down to "ok, that's pretty
>> odd".
>>
>> So how about fixing that, and also fixing the naming of the function. Call
>> it "kernel_stack_pointer()" to match its more widely used sibling function
>> "user_stack_pointer()".
>>
>> IOW, something like this?
>>
>> Linus
>>
>> ---
>> arch/x86/include/asm/ptrace.h | 7 ++++---
>> arch/x86/oprofile/backtrace.c | 2 +-
>> 2 files changed, 5 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
>> index e304b66..624f133 100644
>> --- a/arch/x86/include/asm/ptrace.h
>> +++ b/arch/x86/include/asm/ptrace.h
>> @@ -187,14 +187,15 @@ static inline int v8086_mode(struct pt_regs *regs)
>>
>> /*
>> * X86_32 CPUs don't save ss and esp if the CPU is already in kernel mode
>> - * when it traps. So regs will be the current sp.
>> + * when it traps. The previous stack will be directly underneath the saved
>> + * registers, and 'sp/ss' won't even have been saved. Thus the '&regs->sp'.
>> *
>> * This is valid only for kernel mode traps.
>> */
>> -static inline unsigned long kernel_trap_sp(struct pt_regs *regs)
>> +static inline unsigned long kernel_stack_pointer(struct pt_regs *regs)
>
> Why not have it return an unsigned long *?
>> {
>> #ifdef CONFIG_X86_32
>> - return (unsigned long)regs;
>> + return (unsigned long)(&regs->sp);
>> #else
>> return regs->sp;

Perhaps, you might forget that this line needs a cast :-).

Anyway, IMHO, it does not come from coding, but meaning.
kernel/user_stack_pointer() just return
"the value of stack pointer register", not a "stack pointer".

Thank you,

>> #endif
>> diff --git a/arch/x86/oprofile/backtrace.c b/arch/x86/oprofile/backtrace.c
>> index 04df67f..044897b 100644
>> --- a/arch/x86/oprofile/backtrace.c
>> +++ b/arch/x86/oprofile/backtrace.c
>> @@ -76,9 +76,9 @@ void
>> x86_backtrace(struct pt_regs * const regs, unsigned int depth)
>> {
>> struct frame_head *head = (struct frame_head *)frame_pointer(regs);
>> - unsigned long stack = kernel_trap_sp(regs);
>>
>> if (!user_mode_vm(regs)) {
>> + unsigned long stack = kernel_stack_pointer(regs);
>
> Make this an unsigned long *?
>
>> if (depth)
>> dump_trace(NULL, regs, (unsigned long *)stack, 0,
>
> Then get rid of the cast?
>
> Robin

--
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com



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