[PATCH 2/2] arm64: insn: move AARCH64_INSN_SIZE into <asm/insn.h>

[Nathan Chancellor]

On Fri, Jun 18, 2021 at 04:18:35PM +0100, Mark Rutland wrote:
> On Thu, Jun 17, 2021 at 06:25:27PM -0700, Nathan Chancellor wrote:
> > Hi Mark,
> 
> Hi Nathan,
> 
> > On Wed, Jun 09, 2021 at 11:23:01AM +0100, Mark Rutland wrote:
> > > For histroical reasons, we define AARCH64_INSN_SIZE in
> > > <asm/alternative-macros.h>, but it would make more sense to do so in
> > > <asm/insn.h>. Let's move it into <asm/insn.h>, and add the necessary
> > > include directives for this.
> 
> > I bisected a CONFIG_LTO_CLANG_THIN=y build failure that our CI reported
> > to this patch:
> > 
> > https://builds.tuxbuild.com/1u4Fpx2FQkkgkyPxWtq0Ke4YFCQ/build.log
> 
> Thanks for reporting this; the lopg is really helpful!
> 
> > I have not had a whole ton of time to look into this (dealing with a
> > million fires it seems :^) but it is not immediately obvious to me why
> > this fails because include/linux/build_bug.h is included within
> > arch/arm64/include/asm/insn.h.
> 
> The problem is that with LTO, we patch READ_ONCE(), and <asm/rwonce.h>
> includes <asm/insn.h>, creating a circular include chain:
> 
> 	<linux/build_bug.h>
> 	<linux/compiler.h>
> 	<asm/rwonce.h>
> 	<asm/alternative-macros.h>
> 	<asm/insn.h>
> 	<linux/build-bug.h>
> 
> ... and so when <asm/insn.h> includes <linux/build_bug.h>, none of the
> BUILD_BUG* definitions have happened yet.

Aha, that would certainly explain it. I figured something like this
would be the root cause but figuring out header dependencies is not my
cup of tea.

> Will, are you happy to take the fixup patch below, or would you prefer
> to drop this patch for now?
> 
> Thanks,
> Mark.
> 
> ---->8----
> >From 0acc3d92302f54475d938f55749805adf74faec1 Mon Sep 17 00:00:00 2001
> From: Mark Rutland <mark.rutland at arm.com>
> Date: Fri, 18 Jun 2021 16:11:22 +0100
> Subject: [PATCH] arm64: insn: avoid circular include dependency
> 
> Nathan reports that when building with CONFIG_LTO_CLANG_THIN=y, the
> build fails due to BUILD_BUG_ON() not being defined before its uss in
> <asm/insn.h>.
> 
> The problem is that with LTO, we patch READ_ONCE(), and <asm/rwonce.h>
> includes <asm/insn.h>, creating a circular include chain:
> 
>         <linux/build_bug.h>
>         <linux/compiler.h>
>         <asm/rwonce.h>
>         <asm/alternative-macros.h>
>         <asm/insn.h>
>         <linux/build-bug.h>
> 
> ... and so when <asm/insn.h> includes <linux/build_bug.h>, none of the
> BUILD_BUG* definitions have happened yet.
> 
> To avoid this, let's move AARCH64_INSN_SIZE into a header without any
> dependencies, such that it can always be safely included. At the same
> time, avoid including <asm/alternative.h> in <asm/insn.h>, which should
> no longer be necessary (and doesn't make sense when insn.h is consumed
> by userspace).
> 
> Reported-by: Nathan Chancellor <nathan at kernel.org>
> Signed-off-by: Mark Rutland <mark.rutland at arm.com>
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Will Deacon <will at kernel.org>
> ---
>  arch/arm64/include/asm/alternative-macros.h | 2 +-
>  arch/arm64/include/asm/insn.h               | 5 +----

Looks like arch/arm64/include/asm/insn-def.h is missing from this patch?

If I add one with just the two deleted lines plus a header guard, the
build passes.

Tested-by: Nathan Chancellor <nathan at kernel.org>

Thank you for the quick fix!

Cheers,
Nathan

>  2 files changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/alternative-macros.h b/arch/arm64/include/asm/alternative-macros.h
> index 703fbf310b79..eba3173a2a2c 100644
> --- a/arch/arm64/include/asm/alternative-macros.h
> +++ b/arch/arm64/include/asm/alternative-macros.h
> @@ -3,7 +3,7 @@
>  #define __ASM_ALTERNATIVE_MACROS_H
>  
>  #include <asm/cpucaps.h>
> -#include <asm/insn.h>
> +#include <asm/insn-def.h>
>  
>  #define ARM64_CB_PATCH ARM64_NCAPS
>  
> diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
> index 1430b4973039..6b776c8667b2 100644
> --- a/arch/arm64/include/asm/insn.h
> +++ b/arch/arm64/include/asm/insn.h
> @@ -10,10 +10,7 @@
>  #include <linux/build_bug.h>
>  #include <linux/types.h>
>  
> -#include <asm/alternative.h>
> -
> -/* A64 instructions are always 32 bits. */
> -#define	AARCH64_INSN_SIZE		4
> +#include <asm/insn-def.h>
>  
>  #ifndef __ASSEMBLY__
>  /*
> -- 
> 2.11.0
> 
> 
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