From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on dcvr.yhbt.net X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=AWL,BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED, SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY shortcircuit=no autolearn=ham autolearn_force=no version=3.4.2 Received: from neon.ruby-lang.org (neon.ruby-lang.org [221.186.184.75]) by dcvr.yhbt.net (Postfix) with ESMTP id A39BD1F5AE for ; Sat, 11 Jul 2020 00:25:10 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id C120D1209D3; Sat, 11 Jul 2020 09:24:38 +0900 (JST) Received: from xtrwkhkc.outbound-mail.sendgrid.net (xtrwkhkc.outbound-mail.sendgrid.net [167.89.16.28]) by neon.ruby-lang.org (Postfix) with ESMTPS id D8A451209B7 for ; Sat, 11 Jul 2020 09:24:36 +0900 (JST) Received: by filterdrecv-p3mdw1-75c584b9c6-nzp6n with SMTP id filterdrecv-p3mdw1-75c584b9c6-nzp6n-20-5F0906D9-2 2020-07-11 00:24:57.024563429 +0000 UTC m=+1235727.893140310 Received: from herokuapp.com (unknown) by ismtpd0040p1iad2.sendgrid.net (SG) with ESMTP id SxALWP6GRwSb_YiREF46cw for ; Sat, 11 Jul 2020 00:24:56.954 +0000 (UTC) Date: Sat, 11 Jul 2020 00:24:57 +0000 (UTC) From: duerst@it.aoyama.ac.jp Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 74910 X-Redmine-Project: ruby-master X-Redmine-Issue-Tracker: Bug X-Redmine-Issue-Id: 17023 X-Redmine-Issue-Author: larskanis X-Redmine-Issue-Assignee: tenderlovemaking X-Redmine-Sender: duerst X-Mailer: Redmine X-Redmine-Host: bugs.ruby-lang.org X-Redmine-Site: Ruby Issue Tracking System X-Auto-Response-Suppress: All Auto-Submitted: auto-generated X-SG-EID: =?us-ascii?Q?uQY=2F2xNrNfHHTWbKn6MBvvzfU5Pqk9I4lnOVb0CFDutnyYqR5dCxTCQB0JS6BE?= =?us-ascii?Q?d5bFRrJ+be9DLmmelb7uZSUEh+HN7Gu62EYiah+?= =?us-ascii?Q?9B7sT8rHKDFjtDBT=2FFz+g9DAxPd0j4tYYFkxrMs?= =?us-ascii?Q?wUUTs80m3KPo38+GY8OGIP3G=2Fn9qDLJUw2vUJMr?= =?us-ascii?Q?4rCQzJPoWzSU7DgGXcWiRrf8cqdm2L5hmF70UzC?= =?us-ascii?Q?KXM+sSMwQiIl1lrWw=3D?= To: ruby-core@ruby-lang.org X-ML-Name: ruby-core X-Mail-Count: 99120 Subject: [ruby-core:99120] [Ruby master Bug#17023] How to prevent String memory to be relocated in ruby-ffi X-BeenThere: ruby-core@ruby-lang.org X-Mailman-Version: 2.1.15 Precedence: list Reply-To: Ruby developers List-Id: Ruby developers List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Errors-To: ruby-core-bounces@ruby-lang.org Sender: "ruby-core" Issue #17023 has been updated by duerst (Martin D=FCrst). Assignee set to tenderlovemaking (Aaron Patterson) Status changed from Open to Assigned ---------------------------------------- Bug #17023: How to prevent String memory to be relocated in ruby-ffi https://bugs.ruby-lang.org/issues/17023#change-86496 * Author: larskanis (Lars Kanis) * Status: Assigned * Priority: Normal * Assignee: tenderlovemaking (Aaron Patterson) * ruby -v: ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x86_64-linux] * Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN ---------------------------------------- [ruby-ffi](https://github.com/ffi/ffi) allows to pass String objects to C b= y using the `:string` argument type. This way the string memory returned by= `RSTRING_PTR` is passed to the C function. The user has to ensure on Ruby = level that the string isn't GC'ed - as long as it is used on C level. That'= s the contract and this worked with all past ruby versions, but ruby-2.7 in= troduced `GC.compact`, which can relocate strings to another memory locatio= n. This example shows the situation and that the string is relocated although = it is still referenced in ruby code: ```ruby File.write "string-relocate.c", <<-EOC static char *g_str; void set(char* str) { g_str =3D str; } char* get() { return g_str; } EOC system "gcc -shared -fPIC string-relocate.c -o string-relocate.so" require 'ffi' class Foo extend FFI::Library ffi_lib File.expand_path('string-relocate.so') attach_function :set, [:string], :void attach_function :get, [], :string def initialize(count) proc {} # necessary to trigger relocation a =3D "a" * count set(a) GC.verify_compaction_references(toward: :empty, double_heap: true) puts "get(#{count}): #{get} (should be: #{a})" end end Foo.new(23) Foo.new(24) ``` The output looks like so on ruby-2.7.1: ``` get(23): (should be: aaaaaaaaaaaaaaaaaaaaaaa) get(24): aaaaaaaaaaaaaaaaaaaaaaaa (should be: aaaaaaaaaaaaaaaaaaaaaaaa) ``` So using `GC.compact` while a string parameter is in use, both on Ruby and = on C level, can cause invalid memory access. How can this prevented? A C extension is expected to use `rb_gc_mark()` in order to pin the VALUE t= o a memory location. But I couldn't find a way to pin a `VALUE` at the time= the argument is passed to the C function, which is the only point in time = ruby-ffi has access to it. ---Files-------------------------------- string-relocate.rb (653 Bytes) -- = https://bugs.ruby-lang.org/ Unsubscribe: