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Subject: Re: [PATCH 2/2] x86/asm: Fix inline asm call constraints for clang
To: Dmitry Vyukov <dvyukov@google.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>,
        "x86@kernel.org" <x86@kernel.org>, LKML <linux-kernel@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>, Thomas Gleixner <tglx@linutronix.de>,
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        Alexander Potapenko <glider@google.com>,
        Matthias Kaehlcke <mka@chromium.org>, Arnd Bergmann <arnd@arndb.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>
References: <cover.1505846562.git.jpoimboe@redhat.com>
 <31e96e6bcfcb47725e15a093b9c31660dfaad430.1505846562.git.jpoimboe@redhat.com>
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From: "H. Peter Anvin" <hpa@zytor.com>
Message-ID: <7e39ef18-3e60-8cc9-ec4f-1cd02ade171f@zytor.com>
Date: Wed, 20 Sep 2017 10:46:24 -0700
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On 09/20/17 10:38, Dmitry Vyukov wrote:
> 
> I think we need just the frame itself and RSP pointing below this
> frame. If we don't have a frame, CALL instruction will smash whatever
> RSP happens to point to. Compiler doesn't have to setup RSP to point
> below used part of stack in leaf functions.
> 

In the kernel it does.  Redzoning is not allowed in the kernel, because
interrupts or exceptions would also smash the redzone.

	-hpa