On Mon, 19 Mar 2018, Peter Zijlstra wrote:
> 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) <pet...@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)
Why are you not using the shell-cached version which you remove further
down?
Thanks,
tglx
