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From: Pavel Machek <pavel@ucw.cz>
To: Nick Desaulniers <ndesaulniers@google.com>
Cc: Pavel Machek <pavel@denx.de>, Roman Kiryanov <rkir@google.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>,
	linux-pm@vger.kernel.org, Greg KH <gregkh@linuxfoundation.org>,
	Alistair Delva <adelva@google.com>,
	Haitao Shan <hshan@google.com>
Subject: Re: [PATCH] arch: x86: power: cpu: init %gs before __restore_processor_state (clang)
Date: Sat, 19 Sep 2020 00:20:06 +0200	[thread overview]
Message-ID: <20200918222006.GA9613@duo.ucw.cz> (raw)
In-Reply-To: <CAKwvOdnuR9GF2tZuyS7Fe8i-S0W2YZ45qP8xJRm_gf+g+oF4=Q@mail.gmail.com>

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Hi!

> > > When load_TR_desc and load_mm_ldt are inlined into
> > > fix_processor_context due to LTO, they cause
> > > fix_processor_context (or in this case __restore_processor_state,
> > > as fix_processor_context was inlined into __restore_processor_state)
> > > to access the stack canary through %gs, but before
> > > __restore_processor_state has restored the previous value
> > > of %gs properly. LLVM appears to be inlining functions with stack
> > > protectors into functions compiled with -fno-stack-protector,
> > > which is likely a bug in LLVM's inliner that needs to be fixed.
> >
> > That's rather ugly.
> >
> > Would it be easier to simply mark those functions as noinline or
> > something like that?
> 
> It is possible, and a possible solution here.  We discussed that
> internally, and found it to not be great.  You only want to prevent
> inlining across TUs for LTO; currently there's no great way to
> express

You should really be doing such discussion publicly.

I believe this is not performance critical so just disabling inlining
(maybe conditional on clang) is best solution.

> compiler.  You could emulate that somewhat by wrapping the noinline
> attribute in CONFIG_LTO_CLANG, but that doesn't solve allowing
> inlining within the same TU.  If you've been following the thread,

Yep, just do that.

BR,
								Pavel
							

-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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  reply	other threads:[~2020-09-18 22:20 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-15 17:26 rkir
2020-09-15 17:46 ` Borislav Petkov
2020-09-15 17:57   ` Roman Kiryanov
2020-09-15 18:27     ` Borislav Petkov
2020-09-15 18:36       ` Roman Kiryanov
2020-09-15 18:52         ` Borislav Petkov
2020-09-15 18:55           ` Roman Kiryanov
2020-09-18 22:25         ` Pavel Machek
2020-09-21 23:28           ` Roman Kiryanov
2020-10-04  9:59             ` Pavel Machek
2020-09-15 18:00   ` Nick Desaulniers
2020-09-15 18:25     ` Borislav Petkov
2020-09-15 19:51       ` Nick Desaulniers
2020-09-15 20:20         ` Borislav Petkov
2020-09-15 21:49           ` Nick Desaulniers
2020-09-16  9:23             ` Borislav Petkov
2020-09-19 16:48             ` Pavel Machek
2020-09-16  8:17         ` peterz
2020-09-15 20:44     ` Arvind Sankar
2020-09-15 22:17 ` Pavel Machek
2020-09-15 22:21   ` Nick Desaulniers
2020-09-18 22:20     ` Pavel Machek [this message]
2020-09-15 23:13   ` Roman Kiryanov

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