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Re: [Xen-devel] [PATCH RFC for-4.13 08/10] xen/arm: alternative: add auto-nop infrastructure
- To: Julien Grall <julien.grall@xxxxxxx>
- From: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Date: Fri, 27 Sep 2019 15:34:44 +0000
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- Cc: Mark Rutland <mark.rutland@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Will Deacon <will.deacon@xxxxxxx>, "andrii.anisov@xxxxxxxxx" <andrii.anisov@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Fri, 27 Sep 2019 15:34:50 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-topic: [PATCH RFC for-4.13 08/10] xen/arm: alternative: add auto-nop infrastructure
Julien Grall writes:
> From: Mark Rutland <mark.rutland@xxxxxxx>
>
> In some cases, one side of an alternative sequence is simply a number of
> NOPs used to balance the other side. Keeping track of this manually is
> tedious, and the presence of large chains of NOPs makes the code more
> painful to read than necessary.
>
> To ameliorate matters, this patch adds a new alternative_else_nop_endif,
> which automatically balances an alternative sequence with a trivial NOP
> sled.
>
> In many cases, we would like a NOP-sled in the default case, and
> instructions patched in in the presence of a feature. To enable the NOPs
> to be generated automatically for this case, this patch also adds a new
> alternative_if, and updates alternative_else and alternative_endif to
> work with either alternative_if or alternative_endif.
>
> The alternative infrastructure was originally ported from Linux. So this
> is pretty much a straight backport from commit 792d47379f4d "arm64:
> alternative: add auto-nop infrastructure". The only difference is the
> nops macro added as not yet existing in Xen.
>
> Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
> [will: use new nops macro to generate nop sequences]
> Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
> [julien: Add nops and port to Xen]
> Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
Reviewed-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
--
Volodymyr Babchuk at EPAM
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