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Date: Tue, 24 May 2022 08:32:01 -0400
From: Rich Felker <dalias@...c.org>
To: 王洪亮 <wanghongliang@...ngson.cn>
Cc: musl@...ts.openwall.com
Subject: Re: add loongarch64 port v3
On Tue, May 24, 2022 at 05:08:21PM +0800, 王洪亮 wrote:
>
> 在 2022/5/21 下午4:22, Markus Wichmann 写道:
> >>>I'm also not clear on how
> >>>specifying the alignment here helps since any object created in a way
> >>>that the alignment would affect cannot have the FAM present.
> >>>
> >>the __aligned__(16) here used to save 128bit vector later.
> >But it has no effect, right? The array member is offset an integer
> >multiple of sixteen bytes from the start of the structure, so it is
> >already aligned with respect to that, and the declaration adds no
> >further padding (and if it did, common style in both Linux and musl is
> >to explicate the padding). And the pointer to the structure comes from
> >the kernel.
>
> if no __aligned__(16),the struct sigcontext is 8 bytes align,even if
> the extcontext[]
What we've been trying to say is that there are several cases, none of
which seem to need it:
1. You create an object with declared type struct sigcontext. In this
case, the flexible array member at the end is not present at all
(because that's how C works) which means there's no extended
context which needs additional alignment and probably also means
this is not a usable way of creating sigcontext structs.
2. You malloc storage for the object with space for the flexible array
member. In this case the allocation has alignment max_align_t and
everything is fine.
3. You get the object from the kernel pushing it onto the stack in a
signal frame. This is probably actually the only case the type is
usable in, and of course it has whatever alignment the kernel gave
it.
Rich
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