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x86: Force asm-goto
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> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Cc: torvalds@linux-foundation.org Link: https://lkml.kernel.org/r/20180319201327.GJ4043@hirez.programming.kicks-ass.net
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13
Makefile
13
Makefile
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@ -494,6 +494,13 @@ RETPOLINE_CFLAGS_CLANG := -mretpoline-external-thunk
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RETPOLINE_CFLAGS := $(call cc-option,$(RETPOLINE_CFLAGS_GCC),$(call cc-option,$(RETPOLINE_CFLAGS_CLANG)))
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export RETPOLINE_CFLAGS
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# check for 'asm goto'
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ifeq ($(call shell-cached,$(CONFIG_SHELL) $(srctree)/scripts/gcc-goto.sh $(CC) $(KBUILD_CFLAGS)), y)
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CC_HAVE_ASM_GOTO := 1
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KBUILD_CFLAGS += -DCC_HAVE_ASM_GOTO
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KBUILD_AFLAGS += -DCC_HAVE_ASM_GOTO
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endif
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ifeq ($(config-targets),1)
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# ===========================================================================
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# *config targets only - make sure prerequisites are updated, and descend
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@ -658,12 +665,6 @@ KBUILD_CFLAGS += $(call cc-ifversion, -lt, 0409, \
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# Tell gcc to never replace conditional load with a non-conditional one
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KBUILD_CFLAGS += $(call cc-option,--param=allow-store-data-races=0)
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# check for 'asm goto'
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ifeq ($(call shell-cached,$(CONFIG_SHELL) $(srctree)/scripts/gcc-goto.sh $(CC) $(KBUILD_CFLAGS)), y)
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KBUILD_CFLAGS += -DCC_HAVE_ASM_GOTO
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KBUILD_AFLAGS += -DCC_HAVE_ASM_GOTO
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endif
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include scripts/Makefile.kcov
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include scripts/Makefile.gcc-plugins
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@ -181,6 +181,10 @@ ifdef CONFIG_FUNCTION_GRAPH_TRACER
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endif
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endif
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ifndef CC_HAVE_ASM_GOTO
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$(error Compiler lacks asm-goto support.)
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endif
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#
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# Jump labels need '-maccumulate-outgoing-args' for gcc < 4.5.2 to prevent a
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# GCC bug (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=46226). There's no way
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