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From: Thomas Gleixner <tglx@linutronix.de>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@kernel.org, linux-kernel@vger.kernel.org,
	torvalds@linux-foundation.org
Subject: Re: [PATCH 1/2] x86: Force asm-goto
Date: Mon, 19 Mar 2018 20:57:48 +0100 (CET)	[thread overview]
Message-ID: <alpine.DEB.2.21.1803192055410.1520@nanos.tec.linutronix.de> (raw)
In-Reply-To: <20180319154717.652679334@infradead.org>

On Mon, 19 Mar 2018, Peter Zijlstra wrote:

> We want to start using asm-goto to guarantee the absence of dynamic
> branches (and thus speculation).
> 
> A primary prerequisite for this is of course that the compiler
> supports asm-goto. This effecively lifts the minimum GCC version to
> build an x86 kernel to gcc-4.5.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  Makefile          |   13 +++++++------
>  arch/x86/Makefile |    4 ++++
>  2 files changed, 11 insertions(+), 6 deletions(-)
> 
> --- a/Makefile
> +++ b/Makefile
> @@ -494,6 +494,13 @@ RETPOLINE_CFLAGS_CLANG := -mretpoline-ex
>  RETPOLINE_CFLAGS := $(call cc-option,$(RETPOLINE_CFLAGS_GCC),$(call cc-option,$(RETPOLINE_CFLAGS_CLANG)))
>  export RETPOLINE_CFLAGS
>  
> +# check for 'asm goto'
> +ifeq ($(shell $(srctree)/scripts/gcc-goto.sh $(CC) $(KBUILD_CFLAGS)), y)

Why are you not using the shell-cached version which you remove further
down?

Thanks,

	tglx

  reply	other threads:[~2018-03-19 19:58 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-03-19 15:41 [PATCH 0/2] x86: Mandate asm-goto support Peter Zijlstra
2018-03-19 15:41 ` [PATCH 1/2] x86: Force asm-goto Peter Zijlstra
2018-03-19 19:57   ` Thomas Gleixner [this message]
2018-03-19 20:13     ` Peter Zijlstra
2018-03-20 10:00       ` [tip:x86/build] " tip-bot for Peter Zijlstra
2018-03-27 16:43       ` [PATCH 1/2] " Anders Roxell
2018-03-20 15:45   ` Jonathan Corbet
2018-03-20 15:50     ` Peter Zijlstra
2018-03-20 18:44       ` Jonathan Corbet
2018-03-22 12:10       ` Pavel Machek
2018-03-19 15:41 ` [PATCH 2/2] x86: Remove FAST_FEATURE_TESTS Peter Zijlstra
2018-03-20 10:01   ` [tip:x86/build] " tip-bot for Peter Zijlstra

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