From: Jamie Lokier <jamie@shareable.org>
To: Laurent Desnogues <laurent.desnogues@gmail.com>
Cc: "Edgar E. Iglesias" <edgar.iglesias@gmail.com>, qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] [PATCH] User mode: Handle x86_64 vsyscall
Date: Sun, 18 Oct 2009 03:47:35 +0100 [thread overview]
Message-ID: <20091018024734.GA15656@shareable.org> (raw)
In-Reply-To: <761ea48b0910171716p1243c63cqac0f8a4085f84c9b@mail.gmail.com>
Laurent Desnogues wrote:
> A recent compiler (gcc 4.4.0) produces this code for a statically
> compiled program:
>
> 00000000005779e0 <time>:
> 5779e0: 48 83 ec 08 sub $0x8,%rsp
> 5779e4: 48 c7 c0 00 04 60 ff mov $0xffffffffff600400,%rax
> 5779eb: ff d0 callq *%rax
> 5779ed: 48 83 c4 08 add $0x8,%rsp
> 5779f1: c3 retq
Yes. It's a fixed address. See the kernel at
linux/arch/x86/kernel/vsyscall_64.c. There are only 3 vsyscall
functions defined: vgettimeofday, vtime and vgetcpu.
Even though it's a statically linked program, I'm not sure if the
above code will work on really old kernels.
The vsyscall page is different from the vdso, which has variable
address, and the address is supplied to Glibc. vdso provides nearly
the same functions in a different way.
-- Jamie
next prev parent reply other threads:[~2009-10-18 2:47 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-07-11 15:14 [Qemu-devel] [PATCH] User mode: Handle x86_64 vsyscall Laurent Desnogues
2009-10-17 15:42 ` [Qemu-devel] " Laurent Desnogues
2009-10-17 19:57 ` [Qemu-devel] " Edgar E. Iglesias
2009-10-18 0:16 ` Laurent Desnogues
2009-10-18 2:47 ` Jamie Lokier [this message]
2009-10-18 11:23 ` Laurent Desnogues
2009-10-18 3:09 ` Jamie Lokier
2009-10-18 7:17 ` Edgar E. Iglesias
2009-10-18 11:29 ` Laurent Desnogues
2010-02-04 22:15 ` Stefan Weil
2010-02-05 22:57 ` Stefan Weil
2010-02-06 1:37 ` Laurent Desnogues
2010-02-06 7:49 ` Stefan Weil
2010-02-06 23:50 ` Laurent Desnogues
2010-02-07 0:22 ` Jamie Lokier
2010-02-07 3:11 ` malc
2010-02-07 10:06 ` Laurent Desnogues
2010-02-07 23:18 ` Richard Henderson
2010-02-08 14:57 ` Vince Weaver
2010-02-06 20:12 ` Richard Henderson
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