[PATCH] arm: boot/compressed: fix inappropriate Thumb2 mnemonic for __nop

[Ard Biesheuvel]

On 8 June 2017 at 16:29, Russell King - ARM Linux <linux at armlinux.org.uk> wrote:
> Gah, it's rather unfortunate that this has been discovered only a
> few days after the other decompressor fix was merged and hit Linus'
> tree...
>

I guess that is where Arnd found it, although he didn't specify. In
any case, apologies for the breakage and thanks to Arnd for reporting
it.

I have dropped this into the patch system.


> On Thu, Jun 08, 2017 at 12:58:47PM +0000, Ard Biesheuvel wrote:
>> 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 CPU_THUMBONLY builds.
>>
>> Fixes: 06a4b6d009a1 ("ARM: 8677/1: boot/compressed: fix decompressor ...")
>> Reported-by: Arnd Bergmann <arnd at arndb.de>
>> Acked-by: Arnd Bergmann <arnd at arndb.de>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>
>> ---
>>
>> Apologies for the breakage: apparently, the combination CONFIG_THUMB2_KERNEL=y,
>> CONFIG_CPU_THUMBONLY=n and CONFIG_EFI_STUB=y was not among the configurations
>> I tested before sending out the original patch.
>>
>>  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
>>
>> --
>> 2.9.3
>>
>
> --
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