From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gproxy2-pub.mail.unifiedlayer.com (gproxy2-pub.mail.unifiedlayer.com [69.89.18.3]) by sourceware.org (Postfix) with ESMTPS id C09EE3858D28 for ; Wed, 18 Jan 2023 18:47:07 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org C09EE3858D28 Authentication-Results: sourceware.org; dmarc=none (p=none dis=none) header.from=tromey.com Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=tromey.com Received: from cmgw11.mail.unifiedlayer.com (unknown [10.0.90.126]) by progateway4.mail.pro1.eigbox.com (Postfix) with ESMTP id 2A097100476C6 for ; Wed, 18 Jan 2023 18:47:07 +0000 (UTC) Received: from box5379.bluehost.com ([162.241.216.53]) by cmsmtp with ESMTP id IDSlpFckVJceRIDSlpJAG4; Wed, 18 Jan 2023 18:47:07 +0000 X-Authority-Reason: nr=8 X-Authority-Analysis: v=2.4 cv=Or6Kdwzt c=1 sm=1 tr=0 ts=63c83eab a=ApxJNpeYhEAb1aAlGBBbmA==:117 a=ApxJNpeYhEAb1aAlGBBbmA==:17 a=dLZJa+xiwSxG16/P+YVxDGlgEgI=:19 a=IkcTkHD0fZMA:10:nop_charset_1 a=RvmDmJFTN0MA:10:nop_rcvd_month_year a=Qbun_eYptAEA:10:endurance_base64_authed_username_1 a=CCpqsmhAAAAA:8 a=10psJO9psGJRdV8u2w4A:9 a=QEXdDO2ut3YA:10:nop_charset_2 a=i3ACzUuj7-AOF9OFYtzV:22 a=ul9cdbp4aOFLsgKbc677:22 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=tromey.com; s=default; h=Content-Transfer-Encoding:Content-Type:MIME-Version:Message-ID: In-Reply-To:Date:References:Subject:Cc:To:From:Sender:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Id:List-Help:List-Unsubscribe:List-Subscribe: List-Post:List-Owner:List-Archive; bh=fJopQ8Vu3O5+ZGQfxMvAC4QomJ61gZISwfx2kAMvg40=; b=x7+d05ebUI9EOXbCSO0ac02bg6 8NFKPKH7+Gq8hCL6CpbA1eDtf3nfDhbfIQer4GXbQTtlYwWlxDg5JI2X3wrl8yp8dIWq3371HdocN oerp6WM6IOgEzx62+l5IAaueO; Received: from 97-122-76-186.hlrn.qwest.net ([97.122.76.186]:34624 helo=murgatroyd) by box5379.bluehost.com with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1pIDSk-000Ppe-H9; Wed, 18 Jan 2023 11:47:06 -0700 From: Tom Tromey To: =?utf-8?Q?Torbj=C3=B6rn?= SVENSSON via Gdb-patches Cc: =?utf-8?Q?Torbj=C3=B6rn?= SVENSSON , , , Yvan Roux Subject: Re: [PATCH v2 3/4] gdb: dwarf2 generic implementation for caching function data References: <20221118155252.113476-1-torbjorn.svensson@foss.st.com> <20221118155252.113476-4-torbjorn.svensson@foss.st.com> X-Attribution: Tom Date: Wed, 18 Jan 2023 11:47:04 -0700 In-Reply-To: <20221118155252.113476-4-torbjorn.svensson@foss.st.com> (=?utf-8?Q?=22Torbj=C3=B6rn?= SVENSSON via Gdb-patches"'s message of "Fri, 18 Nov 2022 16:52:52 +0100") Message-ID: <878rhz1xzr.fsf@tromey.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - box5379.bluehost.com X-AntiAbuse: Original Domain - sourceware.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - tromey.com X-BWhitelist: no X-Source-IP: 97.122.76.186 X-Source-L: No X-Exim-ID: 1pIDSk-000Ppe-H9 X-Source: X-Source-Args: X-Source-Dir: X-Source-Sender: 97-122-76-186.hlrn.qwest.net (murgatroyd) [97.122.76.186]:34624 X-Source-Auth: tom+tromey.com X-Email-Count: 4 X-Source-Cap: ZWx5bnJvYmk7ZWx5bnJvYmk7Ym94NTM3OS5ibHVlaG9zdC5jb20= X-Local-Domain: yes X-Spam-Status: No, score=-3021.9 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,JMQ_SPF_NEUTRAL,RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_PASS,TXREP autolearn=no autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: >>>>> Torbj=C3=B6rn SVENSSON via Gdb-patches w= rites: > When there is no dwarf2 data for a register, a function can be called > to provide the value of this register. In some situations, it might > not be trivial to determine the value to return and it would cause a > performance bottleneck to do the computation each time. > This patch allows the called function to have a "cache" object that it > can use to store some metadata between calls to reduce the performance > impact of the complex logic. > +struct dwarf2_frame_fn_data > +{ This struct should have some kind of introductory comment, as should the fields. > + struct value *(*fn) (frame_info_ptr this_frame, void **this_cache, > + int regnum); Seems like this should use the fn_prev_register typedef. (But see below.) > + void *data; > + struct dwarf2_frame_fn_data* next; Wrong "*" placement. > +void *dwarf2_frame_get_fn_data (frame_info_ptr this_frame, void **this_c= ache, > + fn_prev_register fn) Wrong formatting. > +void *dwarf2_frame_allocate_fn_data (frame_info_ptr this_frame, > + void **this_cache, > + fn_prev_register fn, unsigned long size) Wrong formatting. > +{ > + struct dwarf2_frame_fn_data *fn_data =3D nullptr; > + struct dwarf2_frame_cache *cache > + =3D dwarf2_frame_cache (this_frame, this_cache); > + > + /* First try to find an existing object. */ > + void *data =3D dwarf2_frame_get_fn_data (this_frame, this_cache, fn); > + if (data) > + return data; > + > + /* No object found, lets create a new instance. */ > + fn_data =3D FRAME_OBSTACK_ZALLOC (struct dwarf2_frame_fn_data); > + fn_data->fn =3D fn; > + fn_data->data =3D frame_obstack_zalloc (size); > + fn_data->next =3D cache->fn_data; > + cache->fn_data =3D fn_data; > + > + return fn_data->data; This API seems a bit weird to me. It seems like the 'fn' parameter is never really used. It's maybe just a sort of cookie. But if so, I think it would be better to just use a 'const void *' or 'const char *' or something like that. (A string is nice because then it can also be seen in the debugger and give a clue where it came from.) Ok, I dug up the follow-up patch and indeed it is just a cookie. I think naming it as such and changing the type would make this more clear. Also in the follow-up I see that it calls dwarf2_frame_fn_data first. So if you're going to go that route, then it seems that dwarf2_frame_allocate_fn_data does not need to find an existing object -- it can just assert there isn't one. > + > +/* Allocate a new instance of the function unique data. */ > + > +extern void *dwarf2_frame_allocate_fn_data (frame_info_ptr this_frame, > + void **this_cache, > + fn_prev_register fn, > + unsigned long size); > + > +/* Retrieve the function unique data for this frame. */ > + > +extern void *dwarf2_frame_get_fn_data (frame_info_ptr this_frame, > + void **this_cache, > + fn_prev_register fn); IMO both of these could use a longer comment. From this it's impossible to tell what the point of them is. thanks, Tom