linux-kernel - Re: [PATCH v4 1/6] arm64: vdso32: Fix syncconfig errors.

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Date:   Thu, 3 Oct 2019 17:16:21 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
Cc:     ard.biesheuvel@...aro.org, ndesaulniers@...gle.com,
        linux-kernel@...r.kernel.org, luto@...nel.org, tglx@...utronix.de,
        will@...nel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 1/6] arm64: vdso32: Fix syncconfig errors.

On Thu, Oct 03, 2019 at 05:00:41PM +0100, Catalin Marinas wrote:
> On Wed, Oct 02, 2019 at 03:41:51PM +0100, Vincenzo Frascino wrote:
> > diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile
> > index 84a3d502c5a5..dfa6a5cb99e4 100644
> > --- a/arch/arm64/Makefile
> > +++ b/arch/arm64/Makefile
> > @@ -53,20 +53,12 @@ $(warning Detected assembler with broken .inst; disassembly will be unreliable)
> >    endif
> >  endif
> >  
> > +COMPATCC ?= $(CROSS_COMPILE_COMPAT)gcc
> > +export COMPATCC
> > +
> >  ifeq ($(CONFIG_GENERIC_COMPAT_VDSO), y)
> > -  CROSS_COMPILE_COMPAT ?= $(CONFIG_CROSS_COMPILE_COMPAT_VDSO:"%"=%)
> > -
> > -  ifeq ($(CONFIG_CC_IS_CLANG), y)
> > -    $(warning CROSS_COMPILE_COMPAT is clang, the compat vDSO will not be built)
> > -  else ifeq ($(strip $(CROSS_COMPILE_COMPAT)),)
> > -    $(warning CROSS_COMPILE_COMPAT not defined or empty, the compat vDSO will not be built)
> > -  else ifeq ($(shell which $(CROSS_COMPILE_COMPAT)gcc 2> /dev/null),)
> > -    $(error $(CROSS_COMPILE_COMPAT)gcc not found, check CROSS_COMPILE_COMPAT)
> > -  else
> > -    export CROSS_COMPILE_COMPAT
> > -    export CONFIG_COMPAT_VDSO := y
> > -    compat_vdso := -DCONFIG_COMPAT_VDSO=1
> > -  endif
> > +  export CONFIG_COMPAT_VDSO := y
> > +  compat_vdso := -DCONFIG_COMPAT_VDSO=1
> >  endif
> 
> With this change, if I don't have any CROSS_COMPILE_COMPAT in my
> environment, the kernel fails to build because COMPATCC becomes gcc
> which cannot build the vdso32. What I really want is not to warn me, nor
> fail to build the kernel when I don't care about the compat vDSO (e.g. I
> have a 64-bit only machine).
> 
> What saved us before was the COMPATCC_IS_ARM_GCC check and a selection
> of the GENERIC_COMPAT_VDSO dependent on this check. This was now dropped
> from the previous version of the patch. We could add something like
> COMPATCC_CAN_LINK.

Ah, the COMPATCC_CAN_LINK idea doesn't help because an x86 gcc can still
link. Maybe only enable CONFIG_COMPAT_VDSO above if CROSS_COMPILE_COMPAT
was set. You could move the COMPATCC setting and export under the
same 'if' block in the Makefile.

-- 
Catalin