[PATCH] ARM: 8680/1: boot/compressed: fix inappropriate Thumb2 mnemonic for __nop

[PATCH] ARM: 8680/1: boot/compressed: fix inappropriate Thumb2 mnemonic for __nop

[Chris Brandt]

From: Ard Biesheuvel <ard.biesheuvel@linaro.org>

[ Upstream commit 60ce2858514ed9ccaf00dc7e9f4dc219537e9855 ]

Commit 06a4b6d009a1 ("ARM: 8677/1: boot/compressed: fix decompressor
header layout for v7-M") fixed an issue in the layout of the header
of the compressed kernel image that was caused by the assembler
emitting narrow opcodes for 'mov r0, r0', and for this reason, the
mnemonic was updated to use the W() macro, which will append the .w
suffix (which forces a wide encoding) if required, i.e., when building
the kernel in Thumb2 mode.

However, this failed to take into account that on Thumb2 kernels built
for CPUs that are also ARM capable, the entry point is entered in ARM
mode, and so the instructions emitted here will be ARM instructions
that only exist in a wide encoding to begin with, which is why the
assembler rejects the .w suffix here and aborts the build with the
following message:

  head.S: Assembler messages:
  head.S:132: Error: width suffixes are invalid in ARM mode -- `mov.w r0,r0'

So replace the W(mov) with separate ARM and Thumb2 instructions, where
the latter will only be used for THUMB2_ONLY builds.

Fixes: 06a4b6d009a1 ("ARM: 8677/1: boot/compressed: fix decompressor ...")
Reported-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Chris Brandt <chris.brandt@renesas.com>
---

For the 4.9.x tree, commit 7b5407843691 was applied, but that caused
an issue for CONFIG_THUMB2 builds as you can see in the commit
message above.

Therefore, this upstream fix (that came 2 weeks later) is also required
in the 4.9.x tree to make it build again.
---
 arch/arm/boot/compressed/efi-header.S | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm/boot/compressed/efi-header.S b/arch/arm/boot/compressed/efi-header.S
index 3f7d1b74c5e0..a17ca8d78656 100644
--- a/arch/arm/boot/compressed/efi-header.S
+++ b/arch/arm/boot/compressed/efi-header.S
@@ -17,7 +17,8 @@
 		@ there.
 		.inst	'M' | ('Z' << 8) | (0x1310 << 16)   @ tstne r0, #0x4d000
 #else
-		W(mov)	r0, r0
+ AR_CLASS(	mov	r0, r0		)
+  M_CLASS(	nop.w			)
 #endif
 		.endm
 
-- 
2.16.1

Re: [PATCH] ARM: 8680/1: boot/compressed: fix inappropriate Thumb2 mnemonic for __nop

[Sasha Levin]

On Wed, May 08, 2019 at 01:59:51PM -0500, Chris Brandt wrote:
>From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>
>[ Upstream commit 60ce2858514ed9ccaf00dc7e9f4dc219537e9855 ]
>
>Commit 06a4b6d009a1 ("ARM: 8677/1: boot/compressed: fix decompressor
>header layout for v7-M") fixed an issue in the layout of the header
>of the compressed kernel image that was caused by the assembler
>emitting narrow opcodes for 'mov r0, r0', and for this reason, the
>mnemonic was updated to use the W() macro, which will append the .w
>suffix (which forces a wide encoding) if required, i.e., when building
>the kernel in Thumb2 mode.
>
>However, this failed to take into account that on Thumb2 kernels built
>for CPUs that are also ARM capable, the entry point is entered in ARM
>mode, and so the instructions emitted here will be ARM instructions
>that only exist in a wide encoding to begin with, which is why the
>assembler rejects the .w suffix here and aborts the build with the
>following message:
>
>  head.S: Assembler messages:
>  head.S:132: Error: width suffixes are invalid in ARM mode -- `mov.w r0,r0'
>
>So replace the W(mov) with separate ARM and Thumb2 instructions, where
>the latter will only be used for THUMB2_ONLY builds.
>
>Fixes: 06a4b6d009a1 ("ARM: 8677/1: boot/compressed: fix decompressor ...")
>Reported-by: Arnd Bergmann <arnd@arndb.de>
>Acked-by: Arnd Bergmann <arnd@arndb.de>
>Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
>Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
>Signed-off-by: Chris Brandt <chris.brandt@renesas.com>
>---
>
>For the 4.9.x tree, commit 7b5407843691 was applied, but that caused
>an issue for CONFIG_THUMB2 builds as you can see in the commit
>message above.
>
>Therefore, this upstream fix (that came 2 weeks later) is also required
>in the 4.9.x tree to make it build again.

I've queued 60ce2858514 for 4.9, thanks!

--
Thanks,
Sasha