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=-4.1 required=3.0 tests=AWL,BAYES_00, 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 061DE1F5AE for ; Sat, 11 Jul 2020 10:12:08 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id 7A352120AA7; Sat, 11 Jul 2020 19:11:27 +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 2BB48120AA6 for ; Sat, 11 Jul 2020 19:11:23 +0900 (JST) Received: by filterdrecv-p3iad2-5b55dcd864-9xqm9 with SMTP id filterdrecv-p3iad2-5b55dcd864-9xqm9-19-5F099061-53 2020-07-11 10:11:45.668971634 +0000 UTC m=+1270944.628056772 Received: from herokuapp.com (unknown) by geopod-ismtpd-3-1 (SG) with ESMTP id ryzoiOLmRmWUKbUXVCIUTg for ; Sat, 11 Jul 2020 10:11:45.597 +0000 (UTC) Date: Sat, 11 Jul 2020 10:11:45 +0000 (UTC) From: nobu@ruby-lang.org Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 74916 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: nobu 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?q8Dly+pU2+3ektTtZVXgZtbJPXwqo7p86jCsvYTW4ByL1F5YbTE5UZhqjdRclF?= =?us-ascii?Q?3wG8=2FtHqhAN9aO=2FFMaWg0oohlfURj7PI6ZgaSfD?= =?us-ascii?Q?pmJufNB8r1=2FRUi3YwIn7ZQWxSJ3K=2F17p184nEZk?= =?us-ascii?Q?+Agh5NWhXNX2Iyy3wUMf8s0K51WSRlt91yhvokc?= =?us-ascii?Q?7hscY10TkfGOIWU23ncv0WNUQOtXZCMgVkLRWI1?= =?us-ascii?Q?yrTwvWFpfqFhBFdg4=3D?= To: ruby-core@ruby-lang.org X-ML-Name: ruby-core X-Mail-Count: 99126 Subject: [ruby-core:99126] [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="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: ruby-core-bounces@ruby-lang.org Sender: "ruby-core" Issue #17023 has been updated by nobu (Nobuyoshi Nakada). Backport changed from 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN to 2.5: DONTNEED, 2.6: DONTNEED, 2.7: REQUIRED Status changed from Assigned to Closed As it doesn't seem to occur in the master but only in 2.7, I'll close this and set "Backport to 2.7" required, although I'm not sure if it is a bug. Aaron, could you tell which commit fixed this? ---------------------------------------- Bug #17023: How to prevent String memory to be relocated in ruby-ffi https://bugs.ruby-lang.org/issues/17023#change-86503 * Author: larskanis (Lars Kanis) * Status: Closed * Priority: Normal * Assignee: tenderlovemaking (Aaron Patterson) * ruby -v: ruby 2.7.1p83 (2020-03-31 revision a0c7c23c9c) [x86_64-linux] * Backport: 2.5: DONTNEED, 2.6: DONTNEED, 2.7: REQUIRED ---------------------------------------- [ruby-ffi](https://github.com/ffi/ffi) allows to pass String objects to C by 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 introduced `GC.compact`, which can relocate strings to another memory location. 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 = 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 = "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 to 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/