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Re: [Xen-devel] [PATCH] xen/typesafe: Force helpers to be always_inline
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 1 Oct 2019 21:59:39 +0100
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- Cc: Juergen Gross <jgross@xxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, WeiLiu <wl@xxxxxxx>, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>, George Dunlap <George.Dunlap@xxxxxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>, Ian Jackson <ian.jackson@xxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 01 Oct 2019 20:59:47 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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On 01/10/2019 09:38, Jan Beulich wrote:
> On 30.09.2019 21:16, Andrew Cooper wrote:
>> Clang in particular has a habit of out-of-lining these and creating multiple
>> local copies of _mfn() and mfn_x(), etc. Override this behaviour.
> Is special casing the typesafe helpers then the right approach? The
> fundamental idea after all is to let the compiler decide. I certainly
> agree that not inlining such trivial functions despite the inline
> keyword looks far from optimal, but if there's such a general issue
> with clang, shouldn't we make "inline" expand to "always_inline"
> uniformly?
Inline handing is a mess.
We currently define inline to __inline__. Undoing this results in build
failures.
Linux currently defines inline to always_inline and they are desperately
trying to undo this (mis)behaviour.
There are a few uses of always_inline for safety purposes (the
speculative helpers). Most uses of always_inline look to be workarounds
for the size-of-asm bug/(mis)feature.
In an ideal world, we wouldn't need it at all, but I definitely don't
think that taking the Linux approach is a clever move. We definitely
have some static inlines which would better not being inline.
~Andrew
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