linux-kernel - Re: [PATCH 0000/2297] [ANNOUNCE, RFC] "Fast Kernel Headers" Tree -v1: Eliminate the Linux kernel's "Dependency Hell"

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Date:   Sat, 8 Jan 2022 13:17:31 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "David S. Miller" <davem@...emloft.net>,
        Ard Biesheuvel <ardb@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Al Viro <viro@...iv.linux.org.uk>, llvm@...ts.linux.dev
Subject: Re: [PATCH 0000/2297] [ANNOUNCE, RFC] "Fast Kernel Headers" Tree
 -v1: Eliminate the Linux kernel's "Dependency Hell"


* Ingo Molnar <mingo@...nel.org> wrote:

> * Nathan Chancellor <nathan@...nel.org> wrote:
> 
> > 5. Build error in arch/arm64/kvm/hyp/nvhe with LTO
> > 
> > With arm64 + CONFIG_LTO_CLANG_THIN=y, I see:
> > 
> > $ make -skj"$(nproc)" ARCH=arm64 LLVM=1 defconfig
> > 
> > $ scripts/config -e LTO_CLANG_THIN
> > 
> > $ make -skj"$(nproc)" ARCH=arm64 LLVM=1 olddefconfig arch/arm64/kvm/hyp/nvhe/
> > ld.lld: error: arch/arm64/kvm/hyp/nvhe/hyp.lds:2: unknown directive: .macro
> > >>> .macro __put, val, name
> > >>> ^
> > make[5]: *** [arch/arm64/kvm/hyp/nvhe/Makefile:51: arch/arm64/kvm/hyp/nvhe/kvm_nvhe.tmp.o] Error 1
> > 
> > I was not able to figure out the exact include chain but CONFIG_LTO
> > causes asm/alternative-macros.h to be included in asm/rwonce.h, which
> > eventually gets included in either asm/cache.h or asm/memory.h.
> > 
> > I managed to solve this with the following diff but I am not sure if
> > there is a better or cleaner way to do that.
> > 
> > diff --git a/arch/arm64/include/asm/rwonce.h b/arch/arm64/include/asm/rwonce.h
> > index 1bce62fa908a..e19572a205d0 100644
> > --- a/arch/arm64/include/asm/rwonce.h
> > +++ b/arch/arm64/include/asm/rwonce.h
> > @@ -5,7 +5,7 @@
> >  #ifndef __ASM_RWONCE_H
> >  #define __ASM_RWONCE_H
> >  
> > -#ifdef CONFIG_LTO
> > +#if defined(CONFIG_LTO) && !defined(LINKER_SCRIPT)
> >  
> >  #include <linux/compiler_types.h>
> >  #include <asm/alternative-macros.h>
> > @@ -66,7 +66,7 @@
> >  })
> >  
> >  #endif	/* !BUILD_VDSO */
> > -#endif	/* CONFIG_LTO */
> > +#endif	/* CONFIG_LTO && !LINKER_SCRIPT */

In any case I've added your fix to the fast-headers tree, with a comment 
that this might just be a workaround.

Thanks,

	Ingo