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From: Peter Zijlstra <peterz@infradead.org>
To: mingo@kernel.org, tglx@linutronix.de
Cc: linux-kernel@vger.kernel.org, torvalds@linux-foundation.org,
	"Peter Zijlstra (Intel)" <peterz@infradead.org>
Subject: [PATCH 1/2] x86: Force asm-goto
Date: Mon, 19 Mar 2018 16:41:25 +0100	[thread overview]
Message-ID: <20180319154717.652679334@infradead.org> (raw)
In-Reply-To: 20180319154124.337947038@infradead.org

[-- Attachment #1: peterz-x86-force-asm-goto.patch --]
[-- Type: text/plain, Size: 1923 bytes --]

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) $(KBUILD_CFLAGS)), y)
+  CC_HAVE_ASM_GOTO := 1
+  KBUILD_CFLAGS += -DCC_HAVE_ASM_GOTO
+  KBUILD_AFLAGS += -DCC_HAVE_ASM_GOTO
+endif
+
 ifeq ($(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

  reply	other threads:[~2018-03-19 22:33 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 ` Peter Zijlstra [this message]
2018-03-19 19:57   ` [PATCH 1/2] x86: Force asm-goto Thomas Gleixner
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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