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From: Tom de Vries <vries@sourceware.org> To: gdb-cvs@sourceware.org Subject: [binutils-gdb] [gdb/symtab] Make per_cu->m_lang atomic Date: Thu, 14 Jul 2022 06:19:14 +0000 (GMT) [thread overview] Message-ID: <20220714061919.BDBB43858C83@sourceware.org> (raw) https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=14dd1080c6127e7ad7566598860a885aa244ff8d commit 14dd1080c6127e7ad7566598860a885aa244ff8d Author: Tom de Vries <tdevries@suse.de> Date: Thu Jul 14 08:19:00 2022 +0200 [gdb/symtab] Make per_cu->m_lang atomic When building gdb with -fsanitize=thread and running test-case gdb.dwarf2/inlined_subroutine-inheritance.exp, we run into a data race between: ... Read of size 1 at 0x7b2000003010 by thread T4: #0 packed<language, 1ul>::operator language() const packed.h:54 #1 dwarf2_per_cu_data::set_lang(language) read.h:363 ... and: ... Previous write of size 1 at 0x7b2000003010 by main thread: #0 dwarf2_per_cu_data::set_lang(language) read.h:365 ... Fix this by making per_cu->m_lang atomic. Tested on x86_64-linux. Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29286 Diff: --- gdb/dwarf2/read.h | 22 +++++++++++++--------- 1 file changed, 13 insertions(+), 9 deletions(-) diff --git a/gdb/dwarf2/read.h b/gdb/dwarf2/read.h index acbe298b310..c2f86a9d367 100644 --- a/gdb/dwarf2/read.h +++ b/gdb/dwarf2/read.h @@ -181,7 +181,7 @@ private: std::atomic<packed<dwarf_unit_type, 1>> m_unit_type {(dwarf_unit_type)0}; /* The language of this CU. */ - packed<language, LANGUAGE_BYTES> m_lang = language_unknown; + std::atomic<packed<language, LANGUAGE_BYTES>> m_lang {language_unknown}; public: /* True if this CU has been scanned by the indexer; false if @@ -351,21 +351,25 @@ public: enum language lang (bool strict_p = true) const { + enum language l = m_lang.load (); if (strict_p) - gdb_assert (m_lang != language_unknown); - return m_lang; + gdb_assert (l != language_unknown); + return l; } void set_lang (enum language lang) { if (unit_type () == DW_UT_partial) return; - if (m_lang == language_unknown) - /* Set if not set already. */ - m_lang = lang; - else - /* If already set, verify that it's the same value. */ - gdb_assert (m_lang == lang); + /* Set if not set already. */ + packed<language, LANGUAGE_BYTES> nope = language_unknown; + if (m_lang.compare_exchange_strong (nope, lang)) + return; + /* If already set, verify that it's the same value. */ + nope = lang; + if (m_lang.compare_exchange_strong (nope, lang)) + return; + gdb_assert_not_reached (); } /* Free any cached file names. */
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