From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756910AbdCUIoK (ORCPT ); Tue, 21 Mar 2017 04:44:10 -0400 Received: from mail-oi0-f66.google.com ([209.85.218.66]:34624 "EHLO mail-oi0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755004AbdCUIoI (ORCPT ); Tue, 21 Mar 2017 04:44:08 -0400 MIME-Version: 1.0 In-Reply-To: <877f3javde.fsf@intel.com> References: <20170320215713.3086140-1-arnd@arndb.de> <877f3javde.fsf@intel.com> From: Arnd Bergmann Date: Tue, 21 Mar 2017 09:44:07 +0100 X-Google-Sender-Auth: iCOJLwUI4vUCwc_l613_kM_hl-M Message-ID: Subject: Re: [PATCH] drm/i915: use static const array for PICK macro To: Jani Nikula Cc: Daniel Vetter , David Airlie , Mika Kuoppala , =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= , Chris Wilson , Imre Deak , Ander Conselvan de Oliveira , Robert Bragg , intel-gfx@lists.freedesktop.org, dri-devel , Linux Kernel Mailing List 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 Tue, Mar 21, 2017 at 9:26 AM, Jani Nikula wrote: > On Mon, 20 Mar 2017, Arnd Bergmann wrote: >> The varargs macro trick in _PIPE3/_PHY3/_PORT3 was meant as an optimization >> to shrink the i915 kernel module by around 1000 bytes. > > Really, I didn't care one bit about the size shrink, I only cared about > making it easier and less error prone to increase the number of args in > a number of places. Maintainability and correctness were the goals. Just > for the record. ;) Ok. My only interest here is the warning about possible stack overflow, though the fact that KASAN considers the array code to be fragile is an indication that it is perhaps actually dangerous: if we ever run into a bug that causes the array index to overflow, we might in theory have a security bug that lets users access arbitrary kernel pointers. While the risk for that actually happening is very low, the original code was safer in that regard. My patch on top of yours merely turns a hypothetical arbitrary stack access into an arbitrary .data access, and I don't even know which one would be worse. Arnd From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH] drm/i915: use static const array for PICK macro Date: Tue, 21 Mar 2017 09:44:07 +0100 Message-ID: References: <20170320215713.3086140-1-arnd@arndb.de> <877f3javde.fsf@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: In-Reply-To: <877f3javde.fsf@intel.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" To: Jani Nikula Cc: Ander Conselvan de Oliveira , David Airlie , Linux Kernel Mailing List , dri-devel , Daniel Vetter , intel-gfx@lists.freedesktop.org List-Id: dri-devel@lists.freedesktop.org T24gVHVlLCBNYXIgMjEsIDIwMTcgYXQgOToyNiBBTSwgSmFuaSBOaWt1bGEKPGphbmkubmlrdWxh QGxpbnV4LmludGVsLmNvbT4gd3JvdGU6Cj4gT24gTW9uLCAyMCBNYXIgMjAxNywgQXJuZCBCZXJn bWFubiA8YXJuZEBhcm5kYi5kZT4gd3JvdGU6Cj4+IFRoZSB2YXJhcmdzIG1hY3JvIHRyaWNrIGlu IF9QSVBFMy9fUEhZMy9fUE9SVDMgd2FzIG1lYW50IGFzIGFuIG9wdGltaXphdGlvbgo+PiB0byBz aHJpbmsgdGhlIGk5MTUga2VybmVsIG1vZHVsZSBieSBhcm91bmQgMTAwMCBieXRlcy4KPgo+IFJl YWxseSwgSSBkaWRuJ3QgY2FyZSBvbmUgYml0IGFib3V0IHRoZSBzaXplIHNocmluaywgSSBvbmx5 IGNhcmVkIGFib3V0Cj4gbWFraW5nIGl0IGVhc2llciBhbmQgbGVzcyBlcnJvciBwcm9uZSB0byBp bmNyZWFzZSB0aGUgbnVtYmVyIG9mIGFyZ3MgaW4KPiBhIG51bWJlciBvZiBwbGFjZXMuIE1haW50 YWluYWJpbGl0eSBhbmQgY29ycmVjdG5lc3Mgd2VyZSB0aGUgZ29hbHMuIEp1c3QKPiBmb3IgdGhl IHJlY29yZC4gOykKCk9rLiBNeSBvbmx5IGludGVyZXN0IGhlcmUgaXMgdGhlIHdhcm5pbmcgYWJv dXQgcG9zc2libGUgc3RhY2sgb3ZlcmZsb3csCnRob3VnaCB0aGUgZmFjdCB0aGF0IEtBU0FOIGNv bnNpZGVycyB0aGUgYXJyYXkgY29kZSB0byBiZSBmcmFnaWxlIGlzCmFuIGluZGljYXRpb24gdGhh dCBpdCBpcyBwZXJoYXBzIGFjdHVhbGx5IGRhbmdlcm91czogaWYgd2UgZXZlciBydW4gaW50bwph IGJ1ZyB0aGF0IGNhdXNlcyB0aGUgYXJyYXkgaW5kZXggdG8gb3ZlcmZsb3csIHdlIG1pZ2h0IGlu IHRoZW9yeQpoYXZlIGEgc2VjdXJpdHkgYnVnIHRoYXQgbGV0cyB1c2VycyBhY2Nlc3MgYXJiaXRy YXJ5IGtlcm5lbCBwb2ludGVycy4KCldoaWxlIHRoZSByaXNrIGZvciB0aGF0IGFjdHVhbGx5IGhh cHBlbmluZyBpcyB2ZXJ5IGxvdywgdGhlIG9yaWdpbmFsIGNvZGUKd2FzIHNhZmVyIGluIHRoYXQg cmVnYXJkLiBNeSBwYXRjaCBvbiB0b3Agb2YgeW91cnMgbWVyZWx5IHR1cm5zIGEKaHlwb3RoZXRp Y2FsIGFyYml0cmFyeSBzdGFjayBhY2Nlc3MgaW50byBhbiBhcmJpdHJhcnkgLmRhdGEgYWNjZXNz LAphbmQgSSBkb24ndCBldmVuIGtub3cgd2hpY2ggb25lIHdvdWxkIGJlIHdvcnNlLgoKICAgICBB cm5kCl9fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fCkludGVs LWdmeCBtYWlsaW5nIGxpc3QKSW50ZWwtZ2Z4QGxpc3RzLmZyZWVkZXNrdG9wLm9yZwpodHRwczov L2xpc3RzLmZyZWVkZXNrdG9wLm9yZy9tYWlsbWFuL2xpc3RpbmZvL2ludGVsLWdmeAo=