Now that we have objtool to validate the correctness of asm-goto
constructs we can start using it 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) <pet...@infradead.org>
---
Makefile | 13 +++++++------
arch/x86/Makefile | 4 ++++
2 files changed, 11 insertions(+), 6 deletions(-)
--- a/Makefile
+++ b/Makefile
@@ -513,6 +513,13 @@ ifneq ($(filter install,$(MAKECMDGOALS))
endif
endif
+# check for 'asm goto'
+ifeq ($(shell $(CONFIG_SHELL) $(srctree)/scripts/gcc-goto.sh $(CC)
$(KBUILD_CFLAGS)), y)
+ CC_HAVE_ASM_GOTO := 1
+ KBUILD_CFLAGS += -DCC_HAVE_ASM_GOTO
+ KBUILD_AFLAGS += -DCC_HAVE_ASM_GOTO
+endif
+
ifeq ($(mixed-targets),1)
# ===========================================================================
# We're called with mixed targets (*config and build targets).
@@ -652,12 +659,6 @@ KBUILD_CFLAGS += $(call cc-ifversion, -l
# Tell gcc to never replace conditional load with a non-conditional one
KBUILD_CFLAGS += $(call cc-option,--param=allow-store-data-races=0)
-# check for 'asm goto'
-ifeq ($(shell $(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.gcc-plugins
ifdef CONFIG_READABLE_ASM
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -186,6 +186,10 @@ 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
