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=-3.3 required=3.0 tests=AWL,BAYES_00, MAILING_LIST_MULTI,RCVD_IN_BL_SPAMCOP_NET,RCVD_IN_DNSWL_MED, SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY shortcircuit=no autolearn=no 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 2CC251F5AE for ; Wed, 22 Jul 2020 18:23:21 +0000 (UTC) Received: from neon.ruby-lang.org (localhost [IPv6:::1]) by neon.ruby-lang.org (Postfix) with ESMTP id 937FA1209CF; Thu, 23 Jul 2020 03:22:50 +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 996801209CE for ; Thu, 23 Jul 2020 03:22:48 +0900 (JST) Received: by filterdrecv-p3iad2-5b55dcd864-622mb with SMTP id filterdrecv-p3iad2-5b55dcd864-622mb-16-5F188413-4D 2020-07-22 18:23:15.621802627 +0000 UTC m=+2250835.931248882 Received: from herokuapp.com (unknown) by geopod-ismtpd-3-2 (SG) with ESMTP id gpap-PWuSduADgIuqDubKQ for ; Wed, 22 Jul 2020 18:23:15.609 +0000 (UTC) Date: Wed, 22 Jul 2020 18:23:15 +0000 (UTC) From: tenderlove@ruby-lang.org Message-ID: References: Mime-Version: 1.0 X-Redmine-MailingListIntegration-Message-Ids: 75065 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: tenderlovemaking 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?lWh=2FbSnEjJFRTUHRj45oOQBme8zohdTU9K3TxrDAbWJ6+3Hzebb8wfm4xBZdOu?= =?us-ascii?Q?AFx9zAFVe6VcA19rx=2FSoYKSgtygYRUs3wB7ftJN?= =?us-ascii?Q?wV3DbW8YLPa6QDqHtpzTRN43ivFjdqJjIlAeRhZ?= =?us-ascii?Q?A+NTFn1IENK5=2Fste4KduaJcMg3w8KABpvBoHU7=2F?= =?us-ascii?Q?PkM7Aq++ISdxj42DM=2FslRyt4iR7FaxDFwrPOS0D?= =?us-ascii?Q?jD=2FOszzdfgAiQjVCA=3D?= To: ruby-core@ruby-lang.org X-ML-Name: ruby-core X-Mail-Count: 99276 Subject: [ruby-core:99276] [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 tenderlovemaking (Aaron Patterson). Eregon (Benoit Daloze) wrote in #note-15: > Maybe we need a pin function that doesn't mind if the String is frozen? > After all pinning doesn't change the String contents. I think Lars was having trouble expanding strings that are frozen, not pinning them. I suggested that strings could be expanded such that they cannot be embedded in the Ruby object, and this technique doesn't work on frozen strings. ---------------------------------------- Bug #17023: How to prevent String memory to be relocated in ruby-ffi https://bugs.ruby-lang.org/issues/17023#change-86664 * 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: DONE ---------------------------------------- [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) 0001-Only-marked-objects-should-be-considered-movable.patch (1.23 KB) -- https://bugs.ruby-lang.org/