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

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Message-ID: <20160106175948.GA16647@pd.tnic>
Date:	Wed, 6 Jan 2016 18:59:49 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Tony Luck <tony.luck@...el.com>, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Robert <elliott@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	linux-nvdimm <linux-nvdimm@...1.01.org>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH v7 1/3] x86: Add classes to exception tables

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.

> > +       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?

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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