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 X-Spam-Level: X-Spam-Status: No, score=-11.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E4687C433DF for ; Wed, 19 Aug 2020 14:53:06 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 93FF32083B for ; Wed, 19 Aug 2020 14:53:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="ho+zMHTu" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 93FF32083B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=qQ7QSWQXKDDaY7RjZUeLO8ChK8e02F+pxmwPxtOec/s=; b=ho+zMHTuyTutU6jZnewC6qMWx zhRHgPa3Gu0naR1NfRpVvIdxsawV1PrBa2tTyDkckEjcAdsJK8VQD0m3+razraStL3esUxPjWykch htZLOioNlSpOwZEdP8cK/bSFfXGwelSjrsSogxiD011CYNsFG+g/fdvvS1CHXlkZRP3ZcyiBtmSIw wBLXRPFG9XPd+jAh4Nh5kkzHwZkjZ4tJOTVfwqBaGx0qvHLf+GSjQnqHkKsLUi7CQJZt6w2mjpCw+ /AXAM6B7F/lxTc3tetoi7a0cVl9CVxHukoIzpl+yGJnpOGzhIBehDWf8Qn8/r8H7PL7V3gaPYqaLN zcHpPITYg==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1k8PQy-0007CJ-Ii; Wed, 19 Aug 2020 14:51:24 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1k8PQw-0007Bv-31 for linux-arm-kernel@lists.infradead.org; Wed, 19 Aug 2020 14:51:23 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id AEEDB1045; Wed, 19 Aug 2020 07:51:16 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CD2273F71F; Wed, 19 Aug 2020 07:51:14 -0700 (PDT) Date: Wed, 19 Aug 2020 15:51:12 +0100 From: Dave Martin To: Peter Collingbourne Subject: Re: [PATCH v9 4/6] signal: define the SA_UNSUPPORTED bit in sa_flags Message-ID: <20200819145112.GG6642@arm.com> References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200819_105122_236616_C6558E35 X-CRM114-Status: GOOD ( 27.89 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Linux ARM , linux-parisc@vger.kernel.org, Catalin Marinas , Kevin Brodsky , Oleg Nesterov , "James E.J. Bottomley" , Kostya Serebryany , "Eric W. Biederman" , Andrey Konovalov , David Spickett , Vincenzo Frascino , Will Deacon , Evgenii Stepanov , Richard Henderson Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Aug 17, 2020 at 08:33:49PM -0700, Peter Collingbourne wrote: > This bit will never be supported in the uapi. The purpose of this flag > bit is to allow userspace to distinguish an old kernel that does not > clear unknown sa_flags bits from a kernel that supports every flag bit. > > In other words, if userspace finds that this bit remains set in > oldact.sa_flags, it means that the kernel cannot be trusted to have > cleared unknown flag bits from sa_flags, so no assumptions about flag > bit support can be made. > > Signed-off-by: Peter Collingbourne > --- > View this change in Gerrit: https://linux-review.googlesource.com/q/Ic2501ad150a3a79c1cf27fb8c99be342e9dffbcb > > include/uapi/asm-generic/signal-defs.h | 7 +++++++ > kernel/signal.c | 6 ++++++ > 2 files changed, 13 insertions(+) > > diff --git a/include/uapi/asm-generic/signal-defs.h b/include/uapi/asm-generic/signal-defs.h > index 91000b6b97e0..c30a9c1a77b2 100644 > --- a/include/uapi/asm-generic/signal-defs.h > +++ b/include/uapi/asm-generic/signal-defs.h > @@ -13,6 +13,12 @@ > * SA_RESETHAND clears the handler when the signal is delivered. > * SA_NOCLDWAIT flag on SIGCHLD to inhibit zombies. > * SA_NODEFER prevents the current signal from being masked in the handler. > + * SA_UNSUPPORTED is a flag bit that will never be supported. Kernels from > + * before the introduction of SA_UNSUPPORTED did not clear unknown bits from > + * sa_flags when read using the oldact argument to sigaction and rt_sigaction, > + * so this bit allows flag bit support to be detected from userspace while > + * allowing an old kernel to be distinguished from a kernel that supports every > + * flag bit. > * > * SA_ONESHOT and SA_NOMASK are the historical Linux names for the Single > * Unix names RESETHAND and NODEFER respectively. > @@ -42,6 +48,7 @@ > * The following bits are used in architecture-specific SA_* definitions and > * should be avoided for new generic flags: 3, 4, 5, 6, 7, 8, 9, 16, 24, 25, 26. > */ > +#define SA_UNSUPPORTED 0x00000400 This concept confused me a bit initially, since in a sense this flag is supported, just with a rather peculiar meaning. Since the main (only) purpose of this bit will be to check whether SA_XFLAGS is actually supported, I wonder whether it makes sense to weld the two together, say: #define SA_REQUEST_XFLAGS 0x00000c00 #define SA_XFLAGS_MASK 0x00000c00 #define SA_HAVE_XFLAGS 0x00000800 This is a departure from the current style of definitions though. sa.sa_flags |= SA_REQUEST_XFLAGS; sigaction(..., &sa, &sa); if ((sa.sa_flags & SA_XFLAGS_MASK) == SA_HAVE_XFLAGS) /* xflags available */ This would require some juggling of the way SA_UAPI_FLAGS works though. Maybe not worth it, so long as the semantics get clearly documented. [...] Cheers ---Dave _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel