On Thu, 2012-09-06 at 12:04 +0200, Robert Richter wrote:
> please take a look at this. Not sure if Linus want to look at this too
> and if we need more optimization here.
It could probably go either way. Although the function has several
lines, it looks like the actual assembly produced wouldn't be much. I
took a quick look at where kernel_stack_pointer() is used, and I didn't
find any hot paths. This is why I think it can either be a called
function or static inline without much difference.
>
> #define GET_IP(regs) ((regs)->ip)
> #define GET_FP(regs) ((regs)->bp)
> diff --git a/arch/x86/kernel/ptrace.c b/arch/x86/kernel/ptrace.c
> index c4c6a5c..5a9a8c9 100644
> --- a/arch/x86/kernel/ptrace.c
> +++ b/arch/x86/kernel/ptrace.c
> @@ -165,6 +165,27 @@ static inline bool invalid_selector(u16 value)
>
> #define FLAG_MASK FLAG_MASK_32
>
> +/*
> + * X86_32 CPUs don't save ss and esp if the CPU is already in kernel mode
> + * when it traps. The previous stack will be directly underneath the saved
> + * registers, and 'sp/ss' won't even have been saved. Thus the '®s->sp'.
> + *
> + * This is valid only for kernel mode traps.
> + */
> +unsigned long kernel_stack_pointer(struct pt_regs *regs)
> +{
> + unsigned long context = (unsigned long)regs & ~(THREAD_SIZE - 1);
> + unsigned long sp = (unsigned long)®s->sp;
> + struct thread_info *tinfo;
> +
Please add some comments to why you did this. Having this info in just
the change log is not enough. Reading it with the code makes much more
sense.
> + if (context == (sp & ~(THREAD_SIZE - 1)))
> + return sp;
> +
> + tinfo = (struct thread_info *)context;
> +
> + return tinfo->previous_esp;
> +}
> +
> static unsigned long *pt_regs_access(struct pt_regs *regs, unsigned long
> regno)
> {
> BUILD_BUG_ON(offsetof(struct pt_regs, bx) != 0);
> diff --git a/arch/x86/oprofile/backtrace.c b/arch/x86/oprofile/backtrace.c
> index d6aa6e8..5b5741e 100644
> --- a/arch/x86/oprofile/backtrace.c
> +++ b/arch/x86/oprofile/backtrace.c
> @@ -113,7 +113,7 @@ x86_backtrace(struct pt_regs * const regs, unsigned int
> depth)
>
> if (!user_mode_vm(regs)) {
> unsigned long stack = kernel_stack_pointer(regs);
> - if (depth)
> + if (depth & stack)
Can other users of kernel_stack_pointer() be nailed by a return of NULL?
-- Steve
> dump_trace(NULL, regs, (unsigned long *)stack, 0,
> &backtrace_ops, &depth);
> return;
> --
> 1.7.8.6
>
>
>
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