Re: [RFC -mm][PATCH 5/6] prepare kprobes code for x86 unification

[Masami Hiramatsu <mhiramat at redhat dot com>]

Hi Arjan,

Thank you for comment.
Arjan van de Ven wrote:
> On Mon, 10 Dec 2007 17:53:22 -0500
> Masami Hiramatsu <mhiramat@redhat.com> wrote:
>> +#define stack_addr(regs) ((unsigned long *)&regs->sp)
> 
> Hi,
> 
> thanks for taking up this work again, however this line has a bug (yes it's a bug in the 32 bit retprobes);
> the address of the stack is regs->sp not &regs->sp, since &regs->sp is the address of the 
> memory we store the stackpointer in, not the actual address on the stack...

As far as I know, it is true on x86-64, but it's not true on x86-32(kernel mode).
I checked it in __show_registers()@arch/x86/kernel/process_32.c.

Here is that code:
>         if (user_mode_vm(regs)) {
>                 sp = regs->sp;
>                 ss = regs->ss & 0xffff;
>                 savesegment(gs, gs);
>         } else {
>                 sp = (unsigned long) (&regs->sp);
>                 savesegment(ss, ss);
>                 savesegment(gs, gs);
>         }

So, in kernel mode, &regs->sp is the address of the top of stack.

Best Regards,

> 
> Greetings,
>   Arjan van de Ven

-- 
Masami Hiramatsu

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

e-mail: mhiramat@redhat.com, masami.hiramatsu.pt@hitachi.com