From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from simark.ca (simark.ca [158.69.221.121]) by sourceware.org (Postfix) with ESMTPS id F2AEA385828E for ; Mon, 6 Feb 2023 20:05:14 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org F2AEA385828E Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=simark.ca Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=simark.ca Received: from [10.0.0.11] (unknown [217.28.27.60]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by simark.ca (Postfix) with ESMTPSA id 480011E112; Mon, 6 Feb 2023 15:05:10 -0500 (EST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=simark.ca; s=mail; t=1675713914; bh=PS/cEaqQEeyL1nOuFRzq1GISJIdPeha7nHMNi496E8U=; h=Date:Subject:To:References:From:In-Reply-To:From; b=Ii50R4LvpZPZK7q+4Sd1roq4lqNPiVWKH31MRseMGr5CFl+LcVoOTlVlx0+2QgMqy QGn1Pt14OBVqC8z6OtNdmEN+EFDPGLll7x68vBBnO11OJPx5i5N4cieILPPIQpfesI K5TgnK3JHVaVlb3Ts5q+6leDrS0cFYSZV7xOvEas= Message-ID: Date: Mon, 6 Feb 2023 15:05:09 -0500 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 Subject: Re: [PATCH v3 0/8] gdbserver improvements for AArch64 SVE support Content-Language: en-US To: Pedro Alves , Thiago Jung Bauermann , gdb-patches@sourceware.org References: <20230130044518.3322695-1-thiago.bauermann@linaro.org> <28bdd610-982d-aebb-ebc7-17b6d5fd80ed@palves.net> From: Simon Marchi In-Reply-To: <28bdd610-982d-aebb-ebc7-17b6d5fd80ed@palves.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Spam-Status: No, score=-5.4 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,NICE_REPLY_A,SPF_HELO_PASS,SPF_PASS,TXREP autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: > Ah! I had also suggested to you something like that at the Cauldron (when we were in line > for lunch. :-D However, IIRC, I had suggested that we should be able to cache the tdesc by filename. > > Let me explain -- when we fetch a target description, we actually tell the server > to retrieve a tdesc _by a given filename_. By default, we ask for target.xml, like this: > > qXfer:features:read:target.xml > > but then, the retrieved target.xml file may "xi:include" some other file, like for example these do: > > gdb/features/s390-linux64.xml:14: > gdb/features/s390-linux64.xml:15: > gdb/features/s390-linux64.xml:16: > > (try grepping for xi:include in the gdb/features/ dir for a lot more hits.) > > and so when processing each of those xi:include's, gdb sends another qXfer:features:read packet, > with the corresponding included filename, like e.g., > > qXfer:features:read:s390-core64.xml > > Here's what the manual says: > > @item qXfer:features:read:@var{annex}:@var{offset},@var{length} > @anchor{qXfer target description read} > Access the @dfn{target description}. @xref{Target Descriptions}. The > annex specifies which XML document to access. The main description is > always loaded from the @samp{target.xml} annex. > > So basically I am suggesting that instead a new ID mechanism, we should be able to > use the preexisting annex/filename concept as key. That means that the stop reply and > the thread listing would include a new "tdesc=foo.xml" attribute, instead of this > ID that then is defined to map to "target-id-%u.xml", which is basically admitting > that tdesc filenames exist anyhow. Just for completeness, how do you envision that working for SVE? GDBserver would make up unique names for each configuration, like "target-vq-%d.xml"? If caching using filenames as keys, what is the scope of that namespace? Per remote connection, per inferior? I think it wouldn't work per remote connection, because fetching "target.xml" for two different inferiors could give two different answers. Tangentially, I'm wondering if querying qXfer:features:read (mostly fetching "target.xml" is going to become thread-sensitive. In other words, if GDB set the general thread to a thread with vq == A, gets target.xml, then sets the general thread to a thread with vq == B, then gets target.xml, is it going to get two different target descriptions? I think that it would make sense to do so *. Therefore, caching target.xml per-inferior wouldn't be reliable either. And if included files could vary per thread, you'd have to make sure to give them unique names. * I think that since we're going towards thread-specific tdescs, the process-wide tdesc is going to become an obsolete concept, maybe just kept for backwards compatibility for when an old GDB not aware of per-thread tdescs talks to a new GDBserver aware of it, or vice versa. Simon