From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 66EB4C433EF for ; Thu, 19 May 2022 21:06:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245022AbiESVGi convert rfc822-to-8bit (ORCPT ); Thu, 19 May 2022 17:06:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54098 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S244979AbiESVGg (ORCPT ); Thu, 19 May 2022 17:06:36 -0400 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.85.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 30C8C5BE56 for ; Thu, 19 May 2022 14:06:29 -0700 (PDT) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-94-pLza9LL4PAeN7Tz7PiBzzA-1; Thu, 19 May 2022 22:06:25 +0100 X-MC-Unique: pLza9LL4PAeN7Tz7PiBzzA-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.36; Thu, 19 May 2022 22:06:24 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.036; Thu, 19 May 2022 22:06:24 +0100 From: David Laight To: 'Kent Overstreet' , "linux-kernel@vger.kernel.org" , "linux-mm@vger.kernel.org" , "pmladek@suse.com" , "rostedt@goodmis.org" , "senozhatsky@chromium.org" CC: "andriy.shevchenko@linux.intel.com" , "willy@infradead.org" Subject: RE: [PATCH v2 03/28] vsprintf: %pf(%p) Thread-Topic: [PATCH v2 03/28] vsprintf: %pf(%p) Thread-Index: AQHYa6VkVQCoxy629k+LRSm5RxWDEq0mrmAQ Date: Thu, 19 May 2022 21:06:24 +0000 Message-ID: <141b17a257274fc38291cdb07e0e23b6@AcuMS.aculab.com> References: <20220519172421.162394-1-kent.overstreet@gmail.com> <20220519172421.162394-4-kent.overstreet@gmail.com> In-Reply-To: <20220519172421.162394-4-kent.overstreet@gmail.com> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Kent Overstreet > Sent: 19 May 2022 18:24 > > This implements two new format strings: both do the same thing, one more > compatible with current gcc format string checking, the other that we'd > like to standardize: > > %p(%p) - more compatible > %(%p) - more prettier > > Both can take variable numbers of arguments, i.e. %(%p,%p,%p). > > They're used to indicate that snprintf or pr_buf should interpret the > next argument as a pretty-printer function to call, and subsequent > arguments within the parentheses should be passed to the pretty-printer. I suspect this a very good way to blow the kernel stack. The highest stack use is already very likely to be inside the printf code in an error path somewhere. ... > The goal is to replace most of our %p format extensions with this > interface, and to move pretty-printers out of the core vsprintf.c code - One advantage of the current scheme is that is reasonably safe and easy to use. Perhaps too many extra formats have been added recently. This all seems like a recipe for disaster with functions being called with the wrong number of parameters (I can't think how you can compile-time check it). Double copying using a temporary buffer isn't the end of the world. It is only a problem because pr_cont() is basically impossible. But since kernel printf ought to be formatted to reasonable line length that isn't really an issue. printf() is expensive an extra memory copy is probably noise. ... > Currently, we can only call pretty printers with pointer arguments. This > could be changed to also allow at least integer arguments in the future > by using libffi. I'm sure I remember something else trying to use that. IIRC it is basically broken by design. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)