From: "James Y Knight via gnu-gabi" <gnu-gabi@sourceware.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: gnu-gabi@sourceware.org
Subject: Re: gABI extension proposal: PT_SHMMAP
Date: Sun, 01 Jan 2017 00:00:00 -0000 [thread overview]
Message-ID: <CAA2zVHqBowJEUjSNQw_867_79_FsSKJLLxf9GQQA+r+fGPToUQ@mail.gmail.com> (raw)
In-Reply-To: <5d71c4e4-19d2-3861-e212-5e86d29c53fc@zytor.com>
Why is MAP_SHARED even needed for the linux vdso use-case?
All the mappings created for the vdso are read-only mappings, right?
And on Linux, MAP_PRIVATE mappings already reflect changes made to the
underlying file, so long as the process hasn't written to the page, I
think?
So, if you're intending to use this to implement the "vvar" mapping,
isn't the default MAP_PRIVATE already sufficient?
On Wed, May 31, 2017 at 5:23 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>
> Hello,
>
> I would like to propose an extension to the ELF gABI, which is analogous
> to PT_LOAD except that it requests that the underlying file be
> memory-mapped with MAP_SHARED, rather than MAP_PRIVATE as used for
> PT_LOAD. PT_SHARED or PT_SHLOAD would be other possible names.
>
> The main motivation for this is to allow the Linux kernel vDSO to
> finally become as close to an "ordinary" ELF DSO as is possible. The
> vDSO depends on having its kernel-provided data page(s) at a specific
> offset from the vDSO code; this is currently done by ad hoc memory
> areas, which has a number of problems, especially for mixed-mode programs.
>
> The idea is to convert the vdso to a proper file in one of the
> kernel-provided filesystems (e.g. /proc or /sys); by defining this type,
> an ELF parser would be able to create the appropriate mappings without
> any ad hoc code.
>
> This may be usable for other operating systems or perhaps even in
> userspace. However, if there is no such interest then it would be
> possible for Linux to use one of the PT_*OS constants; however, I
> generally believe it is better to try to be as inclusive as possible.
>
> -hpa
next prev parent reply other threads:[~2017-06-07 18:27 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-01 0:00 H. Peter Anvin
2017-01-01 0:00 ` Cary Coutant
2017-01-01 0:00 ` hpa
2017-01-01 0:00 ` Suprateeka R Hegde
2017-01-01 0:00 ` H. Peter Anvin
2017-01-01 0:00 ` James Y Knight via gnu-gabi [this message]
2017-01-01 0:00 ` Cary Coutant
2017-01-01 0:00 ` Suprateeka R Hegde
2017-01-01 0:00 ` H. Peter Anvin
2017-01-01 0:00 ` Suprateeka R Hegde
2017-01-01 0:00 ` H. Peter Anvin
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=CAA2zVHqBowJEUjSNQw_867_79_FsSKJLLxf9GQQA+r+fGPToUQ@mail.gmail.com \
--to=gnu-gabi@sourceware.org \
--cc=hpa@zytor.com \
--cc=jyknight@google.com \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
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 read-only IMAP folder(s) and NNTP newsgroup(s).