Re: [PATCH v7 1/3] x86: Add classes to exception tables

[Andy Lutomirski <luto@amacapital.net>]

On Wed, Jan 6, 2016 at 9:59 AM, Borislav Petkov <bp@alien8.de> wrote:
> On Wed, Jan 06, 2016 at 09:54:19AM -0800, Andy Lutomirski wrote:
>> I assume that this zero is to save the couple of bytes for the
>> relocation entry on relocatable kernels?
>
> I didn't want to touch all _ASM_EXTABLE() macro invocations by adding a
> third param @handler which is redundant as we know which it is.

I see.  You could shove the .long ex_handler_default - . into the
macro, but that would indeed bloat the kernel image a bit more
(although not the in-memory size of the kernel).

>
>> > +       new_ip  = ex_fixup_addr(e);
>> > +       handler = ex_fixup_handler(e);
>> > +
>> > +       if (!handler)
>> > +               handler = ex_handler_default;
>>
>> the !handler condition here will never trigger because the offset was
>> already applied.
>
> Actually, if I do "0 - .", that would overflow the int because current
> location is virtual address and that's 64-bit. Or would gas simply
> truncate it? Lemme check...
>
> Anyway, what we should do instead is simply
>
>         .long 0
>
> to denote that the @handler is implicit.
>
> Right?

Agreed.  I just think that your current fixup_ex_handler
implementation needs adjustment if you do it that way.

--Andy