Re: [musl] add loongarch64 port v3

[Rich Felker <dalias@libc.org>]

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