From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Message-ID: <4E27163A.6090102@mit.edu> Date: Wed, 20 Jul 2011 13:54:02 -0400 From: Andy Lutomirski MIME-Version: 1.0 References: <1310994456-14142-1-git-send-email-richard@nod.at> <1310994456-14142-3-git-send-email-richard@nod.at> In-Reply-To: <1310994456-14142-3-git-send-email-richard@nod.at> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Subject: Re: [PATCH 3/3] um: Implement a x86_64 vDSO To: Richard Weinberger Cc: user-mode-linux-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org List-ID: On 07/18/2011 09:07 AM, Richard Weinberger wrote: > Until now UML had no x86_64 vDSO. > So glibc always used the vsyscall page for gettimeday() > and friends. > Calls to gettimeday() returned falsely the host time and > confused some programs. > > This patch adds a vDSO which turns all __vdso_* calls into > a system call so that UML can trap them. > > As glibc still uses the vsyscall page for static binaries this > patch improves the situation only for dynamic binaries. > > Signed-off-by: Richard Weinberger > + asm("syscall" : "=a" (ret) : > + "0" (__NR_clock_gettime), "D" (clock), "S" (ts) : "memory"); > + The x86-64 ABI and glibc think that rcx, and r11 are clobbered. glibc also thinks that cc is clobbered. I personally think that rdx and r8-r15 ought to be clobbered under the principle that syscall should look like a function call. It's hard to imagine this causing a problem in a function this trivial, though. This applies to the other two syscall instructions as well. --Andy P.S. If you really care, with the changes in tip/x86/vdso, it ought to be possible for UML to trap vsyscalls as well. This would need a change to do_emulate_vsyscall to honor TIF_SYSCALL_EMU with intelligent semantics. I know nothing about ptrace, so I'm not volunteering :)