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Re: [PATCH v2] ARM: Drop ThumbEE support
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Bertrand Marquis <Bertrand.Marquis@xxxxxxx>
- Date: Thu, 4 Dec 2025 10:22:45 +0000
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- Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Hans van Kranenburg <hans@xxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Jan Beulich <JBeulich@xxxxxxxx>, Maximilian Engelhardt <maxi@xxxxxxxxxxxxx>
- Delivery-date: Thu, 04 Dec 2025 10:24:20 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-index: AQHcZQG1izPOHi/67kCiRUDJelIfObURRcsA
- Thread-topic: [PATCH v2] ARM: Drop ThumbEE support
Hi Andrew,
> On 4 Dec 2025, at 10:38, Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>
> It was reported that Xen no longer builds on Debian unstable/sid.
>
> Assembler messages:
> {standard input}:474: Error: unknown or missing system register name at
> operand 1 -- `msr TEECR32_EL1,x0'
> {standard input}:480: Error: unknown or missing system register name at
> operand 1 -- `msr TEEHBR32_EL1,x0'
> {standard input}:488: Error: unknown or missing system register name at
> operand 2 -- `mrs x0,TEECR32_EL1'
> {standard input}:494: Error: unknown or missing system register name at
> operand 2 -- `mrs x0,TEEHBR32_EL1'
> make[5]: *** [Rules.mk:249: arch/arm/domain.o] Error 1
>
> This turns out to be an intentional change in binutils. ThumbEE was dropped
> ahead of ARM v8 (i.e. AArch64).
>
> Xen supports ARM v7+virt extensions so in principle we could #ifdef
> CONFIG_ARM_32 to keep it working. However, there was apparently no use of
> ThumbEE outside of demo code, so simply drop it.
>
> On ThumbEE capable hardware, unconditionally trap ThumbEE instructions, and
> drop the context switching logic for TEE{CR,HBR}32.
>
> Reported-by: Hans van Kranenburg <hans@xxxxxxxxxxx>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Looks good to me:
Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>
Cheers
Bertrand
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