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x86: Force asm-goto

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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) <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]
This commit is contained in:
Peter Zijlstra authored and Thomas Gleixner committed 2018-03-20 10:58:02 +01:00
1 parent edc39c9b45
commit e501ce957a
2 files changed
+11 -6
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Makefile
+7 -6
View File
@@ -494,6 +494,13 @@ RETPOLINE_CFLAGS_CLANG := -mretpoline-external-thunk
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, -lt, 0409, \
# 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
arch/x86/Makefile
+4
View File
@@ -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