Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751694AbaFOTbu (ORCPT ); Sun, 15 Jun 2014 15:31:50 -0400 Received: from terminus.zytor.com ([198.137.202.10]:41628 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750979AbaFOTbr (ORCPT ); Sun, 15 Jun 2014 15:31:47 -0400 User-Agent: K-9 Mail for Android In-Reply-To: References: <21405.44257.742122.786960@gargle.gargle.HOWL> <20140615143500.GP179@brightrain.aerifal.cx> <539DD26B.3060709@zytor.com> <539DDE9C.3010903@zytor.com> <4ab91a07-c46c-485b-895d-b074d36624d6@email.android.com> <90c597c5-f77d-491e-b0b8-dde2027155b5@email.android.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Subject: Re: [RFC 0/2] __vdso_findsym From: "H. Peter Anvin" Date: Sun, 15 Jun 2014 12:31:17 -0700 To: Ian Lance Taylor CC: Andy Lutomirski , Andi Kleen , Rich Felker , Mikael Pettersson , Russ Cox , Linux API , "linux-kernel@vger.kernel.org" , X86 ML Message-ID: <9a4fb9c9-4b1c-4593-a99e-a2ef2325d55d@email.android.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The weak symbols are well-known names. The __vdso symbols are strong. On June 15, 2014 12:22:17 PM PDT, Ian Lance Taylor wrote: >On Sun, Jun 15, 2014 at 12:14 PM, H. Peter Anvin wrote: >> >> If it doesn't, then you incur an additional indirection penalty. The >strong __vdso symbol allows the libc wrapper to fall back to the vdso >implementation, the weak symbol allows three to be no wrapper at all. >This is good. >> >> The reason for changing ABI would be shifting types. This is very >much how glibc manages transitions. > >The purpose of symbol versioning is so that symbols with well known >names, like stat, can continue to use those same names while changing >types. Both old and new programs can continue to use the name stat >and continue to work even though they use different types. > >I don't see how this applies to the kernel VDSO. Those symbols do not >use well-known names; they use names like __vdso_time. If you change >the types used by those symbols, you can change the name as well. >What is the downside? > >Ian -- Sent from my mobile phone. Please pardon brevity and lack of formatting. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/