mailing list of musl libc
 help / color / mirror / code / Atom feed
From: Rich Felker <dalias@libc.org>
To: 王洪亮 <wanghongliang@loongson.cn>
Cc: musl@lists.openwall.com
Subject: Re: [musl] add loongarch64 port v3
Date: Tue, 24 May 2022 08:32:01 -0400	[thread overview]
Message-ID: <20220524123201.GU7074@brightrain.aerifal.cx> (raw)
In-Reply-To: <777071eb-d8c3-eb04-fef4-4f54d6016e8f@loongson.cn>

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

  reply	other threads:[~2022-05-24 12:32 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-05  3:21 王洪亮
2022-05-09  1:34 ` [musl] " 王洪亮
2022-05-11 13:37   ` Rich Felker
2022-05-11 16:08     ` Arnd Bergmann
2022-05-16 14:27 ` [musl] " Rich Felker
2022-05-21  6:38   ` 王洪亮
2022-05-21  8:22     ` Markus Wichmann
2022-05-24  9:08       ` 王洪亮
2022-05-24 12:32         ` Rich Felker [this message]
2022-05-25 10:08           ` 王洪亮
2022-05-25 12:32             ` Rich Felker
2022-05-26  3:07               ` 王洪亮
2022-05-29  6:34                 ` Szabolcs Nagy

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20220524123201.GU7074@brightrain.aerifal.cx \
    --to=dalias@libc.org \
    --cc=musl@lists.openwall.com \
    --cc=wanghongliang@loongson.cn \
    --subject='Re: [musl] add loongarch64 port v3' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Code repositories for project(s) associated with this inbox:

	https://git.vuxu.org/mirror/musl/

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).