Re: [PATCH AUTOSEL 4.19 58/73] x86/build: Fix compiler support check for CONFIG_RETPOLINE

[Greg KH <gregkh@linuxfoundation.org>]

On Tue, Dec 18, 2018 at 02:26:29PM +0100, Gi-Oh Kim wrote:
> On Thu, Dec 13, 2018 at 5:47 AM Sasha Levin <sashal@kernel.org> wrote:
> >
> > From: Masahiro Yamada <yamada.masahiro@socionext.com>
> >
> > [ Upstream commit 25896d073d8a0403b07e6dec56f58e6c33678207 ]
> >
> > It is troublesome to add a diagnostic like this to the Makefile
> > parse stage because the top-level Makefile could be parsed with
> > a stale include/config/auto.conf.
> >
> > Once you are hit by the error about non-retpoline compiler, the
> > compilation still breaks even after disabling CONFIG_RETPOLINE.
> >
> > The easiest fix is to move this check to the "archprepare" like
> > this commit did:
> >
> >   829fe4aa9ac1 ("x86: Allow generating user-space headers without a compiler")
> >
> > Reported-by: Meelis Roos <mroos@linux.ee>
> > Tested-by: Meelis Roos <mroos@linux.ee>
> > Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
> > Acked-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
> > Cc: Borislav Petkov <bp@alien8.de>
> > Cc: Linus Torvalds <torvalds@linux-foundation.org>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Zhenzhong Duan <zhenzhong.duan@oracle.com>
> > Fixes: 4cd24de3a098 ("x86/retpoline: Make CONFIG_RETPOLINE depend on compiler support")
> > Link: http://lkml.kernel.org/r/1543991239-18476-1-git-send-email-yamada.masahiro@socionext.com
> > Link: https://lkml.org/lkml/2018/12/4/206
> > Signed-off-by: Ingo Molnar <mingo@kernel.org>
> > Signed-off-by: Sasha Levin <sashal@kernel.org>
> > ---
> >  arch/x86/Makefile | 10 +++++++---
> >  1 file changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> > index 9298f0f3817a..b84f61bc5e7a 100644
> > --- a/arch/x86/Makefile
> > +++ b/arch/x86/Makefile
> > @@ -223,9 +223,6 @@ KBUILD_CFLAGS += -fno-asynchronous-unwind-tables
> >
> >  # Avoid indirect branches in kernel to deal with Spectre
> >  ifdef CONFIG_RETPOLINE
> > -ifeq ($(RETPOLINE_CFLAGS),)
> > -  $(error You are building kernel with non-retpoline compiler, please update your compiler.)
> > -endif
> >    KBUILD_CFLAGS += $(RETPOLINE_CFLAGS)
> >  endif
> >
> > @@ -303,6 +300,13 @@ ifndef CC_HAVE_ASM_GOTO
> >         @echo Compiler lacks asm-goto support.
> >         @exit 1
> >  endif
> > +ifdef CONFIG_RETPOLINE
> > +ifeq ($(RETPOLINE_CFLAGS),)
> > +       @echo "You are building kernel with non-retpoline compiler." >&2
> > +       @echo "Please update your compiler." >&2
> > +       @false
> > +endif
> > +endif
> >
> >  archclean:
> >         $(Q)rm -rf $(objtree)/arch/i386
> > --
> > 2.19.1
> >
> 
> 
> Hi Greg,
> 
> I think this patch needs to be merged to linux-stable 4.14.y branch.
> I found out the same problem when I built my drivers on linux-stable 4.14.86.
> Following is what I did to reproduce the problem.
> The problem is gone after applying the patch.

Yes, it needs to get into 4.19.y now as well, I've queued it up.

thanks,

greg k-h