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Date: Wed, 19 Jul 2017 18:30:24 -0500
From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Kees Cook <keescook@chromium.org>
Cc: Ingo Molnar <mingo@kernel.org>, Peter Zijlstra <peterz@infradead.org>,
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Subject: Re: [PATCH v6 2/2] x86/refcount: Implement fast refcount overflow
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On Wed, Jul 19, 2017 at 04:12:37PM -0700, Kees Cook wrote:
> On Wed, Jul 19, 2017 at 12:37 PM, Josh Poimboeuf <jpoimboe@redhat.com> wrote:
> > +#define ASM_UNREACHABLE                                                        \
> > +       "999: .pushsection .discard.unreachable\n\t"                    \
> > +       ".long 999b - .\n\t"                                            \
> > +       ".popsection\n\t"
> 
> Will this end up running into the same bug fixed with
> 3d1e236022cc1426b0834565995ddee2ca231cee and the __LINE__ macro? I
> could tell under which conditions gcc would do this kind of merging...

I hope not, but objtool should complain about it if it does.

We could involve the __LINE__ macro, or some other way to make the
labels unique, but that might complicate the code a bit, so we can delay
doing that unless necessary.

-- 
Josh