Re: [PATCH v2 6/8] x86/entry: add unwind hint annotations

[Andy Lutomirski]

On Fri, Jun 30, 2017 at 8:55 AM, Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote:
> On Fri, Jun 30, 2017 at 08:44:40AM -0700, Andy Lutomirski wrote:
>> > A few comments about the first patch:
>> >
>> >   https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/entry_irq_stack&id=3e2aa2102cc1c5e60d4a8637bff78d0478a55059
>> >
>> > - It uses a '693:' label instead of '.Lirqs_off_\@:'
>>
>> TouchÃ!
>>
>> >
>> > - There's a comment I don't follow:
>> >
>> >     "Anything that can interrupt us here without using IST must be
>> >     *extremely* careful to limit its stack usage."
>> >
>> >   What specifically could interrupt there without using IST?
>>
>> #DB, later on in the series.  I'll update the comment.
>>
>> >
>> > - Since do_softirq_own_stack() is a callable function, I think it still
>> >   needs to save rbp.
>>
>> Whoops.
>>
>> >
>> > - Why change the "jmp error_exit" to "ret" in
>> >   xen_do_hypervisor_callback()?
>>
>> To match the other change I made there.  I removed both.
>
> One more thing I forgot to mention: if you could use r10 instead of r11,
> that would be helpful because it means one less register undwarf needs
> to know about.  (It already deals with r10 because of GCC stack
> realignment).

I'll let you figure that one out :)

(Although I think I agree with hpa: why not let it support all regs?
Or am I missing something  still?)

>
> --
> Josh