Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751722AbaFOTWU (ORCPT ); Sun, 15 Jun 2014 15:22:20 -0400 Received: from mail-oa0-f54.google.com ([209.85.219.54]:49655 "EHLO mail-oa0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751176AbaFOTWS (ORCPT ); Sun, 15 Jun 2014 15:22:18 -0400 MIME-Version: 1.0 In-Reply-To: <90c597c5-f77d-491e-b0b8-dde2027155b5@email.android.com> 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> Date: Sun, 15 Jun 2014 12:22:17 -0700 X-Google-Sender-Auth: AE8XHrPpD7PFdO3WOS3GgleHZzk Message-ID: Subject: Re: [RFC 0/2] __vdso_findsym From: Ian Lance Taylor To: "H. Peter Anvin" Cc: Andy Lutomirski , Andi Kleen , Rich Felker , Mikael Pettersson , Russ Cox , Linux API , "linux-kernel@vger.kernel.org" , X86 ML Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 -- 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/