From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2FACC6116 for ; Wed, 10 Jan 2024 00:29:30 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="cnD/Opmn" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1704846569; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=3UBCSAP+i4rFiL/6w+6TRuBgPaXgWBvM8cIe5uHLFsI=; b=cnD/OpmnzbShIlSU4hg2KWUQb1VjAaLDwQEK8s6f1sy0u6NXzbZ/EsvkP/6hBtAmZs/+/k VtWB0pcRhAMsLOqiWDq6fQTXB2A8Vj2QODoBenVakC3zBIOMlRjplPoWD7SIn4erTjETlr iYBpwnm5npwViQotATcc3RGJerXXfTQ= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-225-rRqSgByQNiiaVW-p7jmNbQ-1; Tue, 09 Jan 2024 19:29:25 -0500 X-MC-Unique: rRqSgByQNiiaVW-p7jmNbQ-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 9EACB82DFE4; Wed, 10 Jan 2024 00:29:25 +0000 (UTC) Received: from warthog.procyon.org.uk (unknown [10.42.28.67]) by smtp.corp.redhat.com (Postfix) with ESMTP id 182D6492BC7; Wed, 10 Jan 2024 00:29:24 +0000 (UTC) Organization: Red Hat UK Ltd. Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom. Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <152261521484.30503.16131389653845029164.stgit@warthog.procyon.org.uk> <3465e0c6-f5b2-4c42-95eb-29361481f805@zytor.com> To: Andrew Pinski Cc: dhowells@redhat.com, "H. Peter Anvin" , linux-kernel@vger.kernel.org Subject: Re: [PATCH 00/45] C++: Convert the kernel to C++ Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <1682636.1704846564.1@warthog.procyon.org.uk> Date: Wed, 10 Jan 2024 00:29:24 +0000 Message-ID: <1682637.1704846564@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.9 Andrew Pinski wrote: > Note even in GCC, we disable exceptions and RTTI while building GCC. > This is specifically due to not wanting to use them and use other > methods to do that. > Note GDB on the other hand used to use setjmp/longjmp for their > exception handling in C and I think they moved over to using C++ > exceptions which simplified things there. But as far as I know the > Linux kernel does not use a mechanism like that (I know of copy > from/to user using HW exceptions/error/interrupt handling but that is > a special case only). If we were to allow exception handling, I wonder if we would actually need to throw anything other than a signed long integer (e.g. an error code) and just disable RTTI. Maybe something like: long sys_rename(...) { struct rwsem_lock lock_a, lock_b; struct inode *dir_a, *dir_b; ... try { if (dir_a > dir_b) { lock_a.down_write_killable(dir_a); lock_b.down_write_killable(dir_b); } else { lock_b.down_write_killable(dir_b); lock_a.down_write_killable(dir_a); } } catch (-EINTR) { throw -ERESTARTSYS; } ... } then have a cut-down exception unwinder that only needs to deal with long values. However, I think rolling out exception handling in the kernel might be too big a task, given the huge amount of code involved - however much we might like to avoid all those return value checks. David