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Commit e501ce95 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Thomas Gleixner
Browse files

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: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: torvalds@linux-foundation.org
Link: https://lkml.kernel.org/r/20180319201327.GJ4043@hirez.programming.kicks-ass.net
parent edc39c9b

Makefile

+7 −6
Original line number Diff line number Diff line
@@ -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 −0
Original line number Diff line number Diff line
@@ -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