From: "Jan Beulich" Subject: Re: [PATCH 2/10] linux 2.6.18: COMPAT_VDSO Date: Mon, 05 Mar 2007 14:48:57 +0000 Message-ID: <45EC3BE9.76E4.0078.0@novell.com> References: <45EC098D.76E4.0078.0@novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Content-Disposition: inline List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Keir Fraser Cc: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org >>> Keir Fraser 05.03.07 14:42 >>> >On 5/3/07 11:14, "Jan Beulich" wrote: > >> This adds support for CONFIG_COMPAT_VDSO. As this will certainly raise >> questions, I left in the code needed for an alternative approach (which >> requires mode C code, but less build script changes). > >I thought COMPAT_VDSO meant that the VDSO had to be mapped at a fixed >location at top of memory, which is impossible when running on Xen? It's gonna be really old libc-s that need an absolutely invariable address. But you certainly recall that in 2.6.16 (and probably earlier) we had a hack to map it in right below PAGE_OFFSET, which worked too for not really new but also not really old libc-s. It is those intermediate libc (supporting AT_SYSINFO but not AT_SYSINFO_EHDR) versions that the option attempts to address for Xen. I happen to have a SuSE 9.0 system still in active use that doesn't work without this option, and I think glibc 2.3.2 shouldn't be considered entirely obsolete, yet. Jan