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Re: [PATCH 2/4] ARM: Fix register constraints in run_in_exception_handler()
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: "Orzel, Michal" <michal.orzel@xxxxxxx>
- Date: Mon, 10 Feb 2025 11:33:13 +0100
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- Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
- Delivery-date: Mon, 10 Feb 2025 10:33:42 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 08/02/2025 01:02, Andrew Cooper wrote:
>
>
> Right now, run_in_exception_handler() takes an input in an arbitrary register,
> and clobbers BUG_FN_REG. This causes the compiler to calculate fn in the
> wrong regsiter.
>
> Instead, use `register asm()` which is the normal way of tying register
> constraints to exact registers.
>
> Bloat-o-meter reports:
>
> ARM64:
> Function old new delta
> dump_registers 356 348 -8
>
> ARM32:
> ns16550_poll 52 48 -4
> dump_registers 432 428 -4
>
> The other instruction dropped in ARM64's dump_registers() is an alignment nop.
>
> No functional change.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
~Michal
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