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
next prev parent 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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