Re: [PATCH 1/2] x86: Force asm-goto

[Thomas Gleixner]

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) <peterz@xxxxxxxxxxxxx>
> ---
>  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