Re: [Patch v2] x86/build: require only gcc use -maccumulate-outgoing-args
From: Josh Poimboeuf
Date: Fri May 05 2017 - 09:05:59 EST
On Thu, May 04, 2017 at 11:38:57PM -0700, hpa@xxxxxxxxx wrote:
> On May 4, 2017 11:23:33 PM PDT, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
> >* Nick Desaulniers <nick.desaulniers@xxxxxxxxx> wrote:
> >> Other compilers, like clang, treat unknown compiler flags as errors.
> >> Signed-off-by: Nick Desaulniers <nick.desaulniers@xxxxxxxxx>
> >> ---
> >> arch/x86/Makefile | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> >> index 4430dd489620..12757a252e6b 100644
> >> --- a/arch/x86/Makefile
> >> +++ b/arch/x86/Makefile
> >> @@ -179,7 +179,7 @@ ifdef CONFIG_JUMP_LABEL
> >> endif
> >> ifeq ($(ACCUMULATE_OUTGOING_ARGS), 1)
> >> - KBUILD_CFLAGS += -maccumulate-outgoing-args
> >> + KBUILD_CFLAGS += $(if $(filter
> >> endif
> >> # Stackpointer is addressed different for 32 bit and 64 bit x86
> >The justification Josh gave for this pattern should be put into a
> >comment and into
> >the changelog as well.
> > Ingo
> However, I don't think Josh's explanation is correct. I am pretty
> sure it is a performance issue, not a correctness issue
Why wouldn't it be a correctness issue? The option is needed in a few
cases (involving older versions of gcc and certain configs) to avoid
some bugs (see the Makefile for more details).
> and besides, a version of gcc that old won't be able to compile the
> kernel for other reasons, as evidenced by the fact that noone has
> complained about this option being mandatory.
Yeah. Looking at the gcc source, the option has actually been around
since 2000. So, never mind!
I'd be ok with v1, plus a comment saying that clang doesn't support the