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Wed, 24 Jan 2018 16:52:28 +0000 Cc: nd@arm.com Subject: Re: A possible libc/dlmopen/pthreads bug To: =?UTF-8?Q?Vivek_Das=c2=a0Mohapatra?= , libc-help@sourceware.org References: From: Szabolcs Nagy Message-ID: <41b64265-397f-1ead-dd79-50052b2d19af@arm.com> Date: Wed, 24 Jan 2018 16:52:00 -0000 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:52.0) Gecko/20100101 Thunderbird/52.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: AM6PR0502CA0001.eurprd05.prod.outlook.com (2603:10a6:209:1::14) To HE1PR0802MB2490.eurprd08.prod.outlook.com (2603:10a6:3:d9::22) X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-HT: Tenant X-MS-Office365-Filtering-Correlation-Id: 8d74d0d1-078d-4ad3-3949-08d5634ada6d X-Microsoft-Antispam: UriScan:;BCL:0;PCL:0;RULEID:(7020095)(4652020)(48565401081)(5600026)(4604075)(2017052603307)(7153060)(7193020);SRVR:HE1PR0802MB2490; X-Microsoft-Exchange-Diagnostics: 1;HE1PR0802MB2490;3:1ihe8Mr9MCEu6lgZL6nWN5m2qI3d7/3DoYZHrgDnsMdNkHcmqkO5+507o1ZXDXrpOA1k/PhfjSPnSvy3DAI+GCW04VO/dRKDAyqWRDMPHq/YdEVk14wXMQ453Tm12nstUdM41NdV9FHiN2gmnCh/VS4Vamc8bIdls/lUXJEAPYnuqRiVglMgF8EnF2UxbNcixDazLVStFDR40J8PqW0Dz6p0QfgwG2p7s8lCgVDxJW8UpFeJIGqpUpQQwEoBeTzU;25:GtTGsy2eO99FONfKiZlCY3M92awFY1cHrBRheaGoys8ztvL6QetuHNDuEsbp5U+a5bN2GxEyf5pf6WUUUABG3/9kQU5GpCJdygcDJh2tYMccu6LY4g8g1HICkAXyHPRjp6wNQZYaNlnrf63QV+xC4cF/YfNCbU+cK+0EV0HimqYSp0g1Zi8jR9Tr2BZ2lxhoLcYmz9uZEd1CegH2zrH6+ifeijvcMq/YvMHNkQNgigC7i63U7WdOYCsnGrwVlZuRY9QvqitZf9dsmUd+Eu3KVHanPlHsR1Q9OQ99IRsKjMD/+F3HGu/6+bALS63TAJ1C5NQA/V4xoz4U9or3U+9nVQ==;31:L+1GJdhVmvQT0yGV/tms2hiuRjjNMJcxL8EEYyEBJvgzGBnFJyGIGYq6ynn63VlrsJ9bdHjU2qXTmkcW/0umAgLpl2ncUo6SFuAdR5/UUyC15OqcV+LDZf5oCtTVNoYNYk+ltTkM4FDttwh/WwPIglkK8TPd2hIa90Q7jQVW06TjhlN5JkTeTAA2UHAxJQl7qGm8wRhvHvdWms+S3IZQ9KF/byUCk7isEFLdr6e7adU= X-MS-TrafficTypeDiagnostic: HE1PR0802MB2490: NoDisclaimer: True X-Microsoft-Exchange-Diagnostics: 1;HE1PR0802MB2490;20:0Ww8/7J+CENX4vAGUViJWRqm6LDAUbGGJMT4dpzpGab3NrhSj6HKA+86OWD0vjGvrwFmFkTevh8Y185f+zP5QI0BluyWRB4VwTytZDJGBtyikm4DFKAuKHaHjAuYMNfpYCVp8zvmW0741jF7pqVLknoDQAy1Jm7dc4w+5M2f3Zg=;4:LVGnvJEFaLsEvWQ1r5VOMr0cziIX85dK3p8vGox1dgZIagfYXR32+7n/wOBNB+XLv7XuLCPljApd59UNMO+76jVc+3FSxiwTgNqM5j6kWh/LhOSLop+6XMDf4/G7SYQa7LGxku0XUyEdbyf1KaILBl137F4sQFDHavH4q4PMrq6r/abQVJ78ZH1R/7npgdFS4Kb9zbCsJHBDdQ1E6haCQrPEQsmzgi1OSNKsLH1tEJyYw1kQuOikBYms0CsjI/bGN6Z3+AQUCr7UM3T6HT4n8Q== X-Microsoft-Antispam-PRVS: X-Exchange-Antispam-Report-Test: UriScan:; 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Is there something I could or should have done to > avoid this? > > A while ago (https://sourceware.org/ml/libc-help/2018-01/msg00002.html) > I suggested a dlmopen flag RTLD_UNIQUE or similar which would cause the > existing mapping of the target library in the main namespace/link-map to be > re-used instead of creating a new one: I believe this would prevent this > problem (and others detailed in that message) from occurring - any thoughts? i don't know what you are doing, but it's hard to imagine that two libcs (or libpthreads) would work in the same process: if they can run code on the same thread they cannot both control the tcb (and will clobber each other's global state through that). same for signal handlers (for internal signals) or brk syscall, or stdio buffering, etc. the libc has to deal with process global/thread local state that must be controlled by the same code consistently otherwise bad things happen.