From: Andi Kleen <ak@muc.de>
To: Bryan Henderson <hbryan@us.ibm.com>
Cc: Paul Taysom <Paul.Taysom@novell.com>,
linux-fsdevel@vger.kernel.org, viro@www.linux.org.uk
Subject: Re: negative seek offsets in VFS
Date: 26 May 2005 21:23:32 +0200
Date: Thu, 26 May 2005 21:23:32 +0200 [thread overview]
Message-ID: <20050526192332.GW86087@muc.de> (raw)
In-Reply-To: <OF71D8EA4F.087D140F-ON8825700D.00613961-8825700D.0061F567@us.ibm.com>
On Thu, May 26, 2005 at 10:49:57AM -0700, Bryan Henderson wrote:
> >The addresses returned from /proc/kallsyms on the x86_64 are negative and
> when
> >I print the address of a kernel variable with "%p" it comes out negative.
>
> Wow. So can someone explain this? Does the x86_64 architecture actually
> have a concept of negative addresses?
Yes, it has. It has a 48bit address space, and the 48th bit
is sign extended to 64bits. So you have a big hole in the middle
and positive and negative address spaces. The kernel uses the negative
half, user space the positive half.
>
> Ordinarily, I'd think this was a bug if I saw it, but I don't see how %p
> could format a minus sign without it being deliberate.
It doesnt, but they are still negative.
> In any case, I know POSIX doesn't have a concept of a negative absolute
> file offset, so a kmem device cannot represent a negative address as a
> negative file offset. A negative loff_t means something else.
I dont think POSIX has anything to say about /dev/kmem.
-Andi
>
next prev parent reply other threads:[~2005-05-26 19:23 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <s29588e0.089@sinclair.provo.novell.com>
2005-05-26 17:49 ` negative seek offsets in VFS Bryan Henderson
2005-05-26 19:23 ` Andi Kleen [this message]
2005-05-26 21:17 ` Bryan Henderson
2005-05-27 10:43 ` Andi Kleen
2005-05-27 18:39 ` Bryan Henderson
2005-05-28 12:41 ` Jamie Lokier
2005-05-31 18:08 ` Bryan Henderson
2005-05-30 9:36 ` Andi Kleen
2005-05-31 18:33 ` Bryan Henderson
2005-05-28 12:37 ` Jamie Lokier
2005-05-30 9:32 ` Andi Kleen
2005-05-26 14:29 Paul Taysom
-- strict thread matches above, loose matches on Subject: below --
2005-05-25 16:39 Andi Kleen
2005-05-25 16:56 ` Trond Myklebust
2005-05-25 18:48 ` Andi Kleen
2005-05-26 0:56 ` Bryan Henderson
2005-05-26 19:20 ` Andi Kleen
2005-05-26 15:15 ` Al Viro
2005-05-26 15:29 ` Linus Torvalds
2005-05-26 19:25 ` Andi Kleen
2005-05-26 19:39 ` Linus Torvalds
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