From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by sourceware.org (Postfix) with ESMTPS id 6B39A3858D1E for ; Wed, 2 Aug 2023 09:53:25 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.2 sourceware.org 6B39A3858D1E Authentication-Results: sourceware.org; dmarc=pass (p=none dis=none) header.from=suse.de Authentication-Results: sourceware.org; spf=pass smtp.mailfrom=suse.de Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out2.suse.de (Postfix) with ESMTPS id 9EE391F749 for ; Wed, 2 Aug 2023 09:53:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_rsa; t=1690970004; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=d/W9XoZo0zEdEa6COA75oAbzB5mivg31zeNt4Bzc7jY=; b=JG3a3XIMndmLKV1mCBFwaTvoCL9hIq+C3dFZJJSknxMSrT8aOPSShqysoFcnUMImFhibDw J5ed3GVn/O3LbvBxEJg4p5LaG6/BJHidYgCG3XDVlSwNo4X+j91twl3B59TQYlzkiFAVI0 U/nA9GvBY0TPQ3qrTKwhKoOeatuPII8= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.de; s=susede2_ed25519; t=1690970004; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc: mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=d/W9XoZo0zEdEa6COA75oAbzB5mivg31zeNt4Bzc7jY=; b=4uk2pz1UqID8A5EhmRndDT5Xcl+R5rfnFTX8+8uETeQGGvOrLUbR5SdFYFYh/WyxI7/Sv3 FGF/l9yj5KnVoADA== Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 89C8313909 for ; Wed, 2 Aug 2023 09:53:24 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id wgN5IJQnymSscgAAMHmgww (envelope-from ) for ; Wed, 02 Aug 2023 09:53:24 +0000 From: Tom de Vries To: gdb-patches@sourceware.org Subject: [PATCH v2 0/6] [gdb/symtab] Fix data-races in gdb.base/index-cache.exp Date: Wed, 2 Aug 2023 11:52:59 +0200 Message-Id: <20230802095305.3668-1-tdevries@suse.de> X-Mailer: git-send-email 2.35.3 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Spam-Status: No, score=-6.2 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,SPF_HELO_NONE,SPF_PASS,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: When building gdb with -fsanitize=thread, we run into a data race in gdb.base/index-cache.exp. Fixing this leads us to another, and so on, so each patch addresses one particular data race, with the exception of the last patch, which extends the test-case a bit. The last patch, when applied without the series runs into a segfault with target board native-extended-gdbserver, filed as PR symtab/30712, but that seems to be fixed by a previous commit in this series. This is the reason for which the patch is part of this series. The first two patches implement the approach mentioned in PR30392 comment 2: ... The reader probably should capture the necessarily globals on the main thread and stash them until the index has been written. ... The 3rd patch cannot be fixed with this approach, so it uses the packed approach: ... - unsigned int queued : 1; + packed queued; ... There's one more patch like that, I checked using pahole that the struct size is not increased. I spent some time convincing myself that the data races on disjoint bitfields are not benign. I started with reading [1], and got convinced by "2.5 Disjoint bit manipulation" in [2]. Also [3] looked interesting, but haven't read it in full. Tested on x86_64-linux, with and without -fsanitize=thread. PR symtab/30392 Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30392 References: [1] https://hacks.mozilla.org/2021/04/eliminating-data-races-in-firefox-a-technical-report/ [2] https://www.usenix.org/legacy/event/hotpar11/tech/final_files/Boehm.pdf [3] https://bartoszmilewski.com/2020/08/11/benign-data-races-considered-harmful/ Tom de Vries (6): [gdb/symtab] Fix data race on index_cache::m_enabled [gdb/symtab] Fix data race on bfd::{cacheable,format} [gdb/symtab] Fix race on dwarf2_per_cu_data::{queued,is_debug_type} [gdb/symtab] Fix data race on bfd_last_cache [gdb/symtab] Fix data race on dwarf2_per_cu_data::{m_header_read_in,is_debug_type} [gdb/testsuite] Extend gdb.base/index-cache.exp gdb/dwarf2/cooked-index.c | 19 ++++++++--- gdb/dwarf2/cooked-index.h | 3 +- gdb/dwarf2/index-cache.c | 46 ++++++++++++++++++++------ gdb/dwarf2/index-cache.h | 25 +++++++++++++- gdb/dwarf2/read.c | 8 ++--- gdb/dwarf2/read.h | 26 +++++++-------- gdb/testsuite/gdb.base/index-cache-2.c | 24 ++++++++++++++ gdb/testsuite/gdb.base/index-cache.c | 6 ++-- gdb/testsuite/gdb.base/index-cache.exp | 22 ++++++++++-- 9 files changed, 141 insertions(+), 38 deletions(-) create mode 100644 gdb/testsuite/gdb.base/index-cache-2.c base-commit: 69c37f53e20dc3e0b3c179b511ff786db6ae114e -- 2.35.3