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

[Mark Rutland]

On Fri, Jun 18, 2021 at 09:53:31AM -0700, Nathan Chancellor wrote:
> 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?

> >  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>

Whoops; that should have been as below.

Was that the same as you tested?

Thanks,
Mark.

---->8----
>From 622fd784c57423b1a276fbbfb270b84839e3afa8 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-def.h           | 9 +++++++++
 arch/arm64/include/asm/insn.h               | 5 +----
 3 files changed, 11 insertions(+), 5 deletions(-)
 create mode 100644 arch/arm64/include/asm/insn-def.h

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-def.h b/arch/arm64/include/asm/insn-def.h
new file mode 100644
index 000000000000..2c075f615c6a
--- /dev/null
+++ b/arch/arm64/include/asm/insn-def.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef __ASM_INSN_DEF_H
+#define __ASM_INSN_DEF_H
+
+/* A64 instructions are always 32 bits. */
+#define	AARCH64_INSN_SIZE		4
+
+#endif /* __ASM_INSN_DEF_H */
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