From: Peter Zijlstra <peterz@infradead.org>
To: Thomas Gleixner <tglx@linutronix.de>
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 21:13:27 +0100 [thread overview]
Message-ID: <20180319201327.GJ4043@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <alpine.DEB.2.21.1803192055410.1520@nanos.tec.linutronix.de>
On Mon, Mar 19, 2018 at 08:57:48PM +0100, Thomas Gleixner wrote:
> 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?
Bah, I'm an idiot. I fixed that up at least two times, but clearly I
forgot to check that again before sending.
---
Subject: x86: Force asm-goto
From: Peter Zijlstra <peterz@infradead.org>
Date: Wed Jan 17 11:42:07 CET 2018
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 ($(call shell-cached,$(CONFIG_SHELL) $(srctree)/scripts/gcc-goto.sh $(CC) $(KBUILD_CFLAGS)), y)
+ CC_HAVE_ASM_GOTO := 1
+ KBUILD_CFLAGS += -DCC_HAVE_ASM_GOTO
+ KBUILD_AFLAGS += -DCC_HAVE_ASM_GOTO
+endif
+
ifeq ($(config-targets),1)
# ===========================================================================
# *config targets only - make sure prerequisites are updated, and descend
@@ -658,12 +665,6 @@ KBUILD_CFLAGS += $(call cc-ifversion, -l
# Tell gcc to never replace conditional load with a non-conditional one
KBUILD_CFLAGS += $(call cc-option,--param=allow-store-data-races=0)
-# check for 'asm goto'
-ifeq ($(call shell-cached,$(CONFIG_SHELL) $(srctree)/scripts/gcc-goto.sh $(CC) $(KBUILD_CFLAGS)), y)
- KBUILD_CFLAGS += -DCC_HAVE_ASM_GOTO
- KBUILD_AFLAGS += -DCC_HAVE_ASM_GOTO
-endif
-
include scripts/Makefile.kcov
include scripts/Makefile.gcc-plugins
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -181,6 +181,10 @@ ifdef CONFIG_FUNCTION_GRAPH_TRACER
endif
endif
+ifndef CC_HAVE_ASM_GOTO
+ $(error Compiler lacks asm-goto support.)
+endif
+
#
# Jump labels need '-maccumulate-outgoing-args' for gcc < 4.5.2 to prevent a
# GCC bug (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=46226). There's no way
next prev parent reply other threads:[~2018-03-19 20:13 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
2018-03-19 20:13 ` Peter Zijlstra [this message]
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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