From: "H. Peter Anvin" <hpa@zytor.com>
To: Andy Lutomirski <luto@amacapital.net>, criu@openvz.org
Cc: Stefani Seibold <stefani@seibold.net>,
linux-kernel@vger.kernel.org, x86@kernel.org, tglx@linutronix.de,
mingo@redhat.com, ak@linux.intel.com, aarcange@redhat.com,
john.stultz@linaro.org
Subject: Re: [PATCH] Add VDSO time function support for x86 32-bit kernel
Date: Thu, 13 Dec 2012 18:18:05 -0800 [thread overview]
Message-ID: <8c3585bc-fc7d-4826-913c-f4581494d91d@email.android.com> (raw)
In-Reply-To: <CALCETrWKDJd1T_VCRNAzD-KTtYBbmvgE_ZYvb8uN4nBUYQvkgA@mail.gmail.com>
Wouldn't the vdso get mapped already and could be mremap()'d. If we really need more control I'd almost push for a device/filesystem node that could be mmapped the usual way.
Andy Lutomirski <luto@amacapital.net> wrote:
>On Thu, Dec 13, 2012 at 5:49 PM, H. Peter Anvin <hpa@zytor.com> wrote:
>> On 12/13/2012 05:42 PM, Andy Lutomirski wrote:
>>>
>>> The 64-bit/x32 case is currently very simple and fast because it
>uses
>>> absolute addressing. Admittedly, pcrel references are free, so
>>> changing this wouldn't cost much. For native, it'll be slower, but
>>> maybe no one cares. I seem to care about this more than anyone
>else,
>>> and I don't use 32 bit code. :)
>>>
>>
>> pcrel is actually cheaper than absolute addressing in 64-bit mode.
>>
>>> The benefit of switching is that the vdso code could be the same in
>>> all three cases. (Actually, it's even better than that. All of the
>>> VVAR magic could be the same in the vdso and the kernel -- the
>kernel
>>> linker script would just have to have an appropriate symbol to see
>the
>>> appropriate mapping.)
>>>
>>>
>>> This:
>>>
>>> __attribute__((visibility("hidden"))) int foo;
>>>
>>> int get_foo(void)
>>> {
>>> return foo;
>>> }
>>>
>>> generates a rip-relative access on 64 bits and GOTOFF on 32 bits.
>>>
>>> The only reason I didn't use a real symbol in the first place is
>>> because I couldn't figure out how to get gcc to emit an absolute
>>> relocation in pic code.
>>
>> Well, then, we wouldn't need to do that... this is starting to sound
>> like a significant win.
>
>How will this avoid breaking checkpoint/restore in userspace? If the
>vdso is not just plain old code, criu presumably needs to know about
>it. Should there be an arch_prctl(ARCH_MAP_VDSO, addr) to create a
>vdso mapping somewhere?
>
>--Andy
--
Sent from my mobile phone. Please excuse brevity and lack of formatting.
next prev parent reply other threads:[~2012-12-14 2:18 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-12-12 20:19 [PATCH] Add VDSO time function support for x86 32-bit kernel stefani
2012-12-12 23:34 ` H. Peter Anvin
2012-12-13 5:53 ` Stefani Seibold
2012-12-13 6:10 ` H. Peter Anvin
2012-12-13 6:14 ` H. Peter Anvin
2012-12-13 6:17 ` Stefani Seibold
2012-12-13 6:47 ` H. Peter Anvin
2012-12-13 7:17 ` Stefani Seibold
2012-12-13 19:32 ` Andy Lutomirski
2012-12-14 0:09 ` H. Peter Anvin
2012-12-14 0:20 ` Andy Lutomirski
2012-12-14 0:36 ` H. Peter Anvin
2012-12-14 1:32 ` H. Peter Anvin
2012-12-14 1:42 ` Andy Lutomirski
2012-12-14 1:49 ` H. Peter Anvin
2012-12-14 2:11 ` Andy Lutomirski
2012-12-14 2:18 ` H. Peter Anvin [this message]
2012-12-14 2:20 ` Andy Lutomirski
2012-12-14 8:34 ` [CRIU] " Pavel Emelyanov
2012-12-14 18:35 ` H. Peter Anvin
2012-12-14 18:44 ` Andy Lutomirski
2012-12-14 18:47 ` H. Peter Anvin
2012-12-14 20:12 ` Cyrill Gorcunov
2012-12-14 21:08 ` H. Peter Anvin
2012-12-14 21:20 ` Cyrill Gorcunov
2012-12-14 21:21 ` H. Peter Anvin
2012-12-14 21:27 ` Andy Lutomirski
2012-12-14 22:00 ` H. Peter Anvin
2012-12-14 22:25 ` Cyrill Gorcunov
2012-12-14 22:27 ` H. Peter Anvin
2012-12-14 22:43 ` Cyrill Gorcunov
2012-12-14 22:48 ` H. Peter Anvin
2012-12-14 23:48 ` John Stultz
2012-12-14 23:55 ` H. Peter Anvin
2012-12-17 9:05 ` Pavel Emelyanov
[not found] ` <fb2e871b-3e2a-4e96-9eb9-cb2dd4f66eaa@email.android! .com>
2012-12-17 15:21 ` H. Peter Anvin
2012-12-17 18:56 ` Pavel Emelyanov
2012-12-17 18:57 ` H. Peter Anvin
2012-12-14 22:46 ` H. Peter Anvin
2012-12-14 23:09 ` Stefani Seibold
2012-12-14 23:29 ` H. Peter Anvin
-- strict thread matches above, loose matches on Subject: below --
2012-12-11 16:11 stefani
2012-12-11 19:27 ` John Stultz
2012-12-11 19:37 ` Andy Lutomirski
2012-12-11 20:54 ` Stefani Seibold
2012-12-11 21:18 ` Andy Lutomirski
2012-12-11 21:28 ` Stefani Seibold
2012-12-11 19:37 ` Andy Lutomirski
2012-12-11 20:40 ` Stefani Seibold
2012-12-12 1:29 ` Andy Lutomirski
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=8c3585bc-fc7d-4826-913c-f4581494d91d@email.android.com \
--to=hpa@zytor.com \
--cc=aarcange@redhat.com \
--cc=ak@linux.intel.com \
--cc=criu@openvz.org \
--cc=john.stultz@linaro.org \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@amacapital.net \
--cc=mingo@redhat.com \
--cc=stefani@seibold.net \
--cc=tglx@linutronix.de \
--cc=x86@kernel.org \
/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 NNTP newsgroup(s).