From 0961970dea995ce9f8750bd615a534bbbd23cefd Mon Sep 17 00:00:00 2001 From: Tom de Vries Date: Fri, 4 Aug 2023 15:05:57 +0200 Subject: [PATCH] [gdb/symtab] Fix data race on dwarf2_per_cu_data::{files_read,is_debug_types} With gdb build with -fsanitize=thread, and the exec from test-case gdb.base/index-cache.exp, I run into: ... $ rm -f ~/.cache/gdb/*; \ gdb -q -batch -iex "set index-cache enabled on" index-cache \ -ex "print foobar" ... WARNING: ThreadSanitizer: data race (pid=25018) Write of size 1 at 0x7b200000410d by main thread: #0 dw2_get_file_names_reader gdb/dwarf2/read.c:2033 (gdb+0x7ab023) #1 dw2_get_file_names gdb/dwarf2/read.c:2130 (gdb+0x7ab023) #2 dw_expand_symtabs_matching_file_matcher(dwarf2_per_objfile*, gdb::function_view) gdb/dwarf2/read.c:3105 (gdb+0x7ac6e9) #3 cooked_index_functions::expand_symtabs_matching(objfile*, gdb::function_view, lookup_name_info const*, gdb::function_view, gdb::function_view, enum_flags, domain_enum, search_domain) gdb/dwarf2/read.c:16812 (gdb+0x7d040f) #4 objfile::map_symtabs_matching_filename(char const*, char const*, gdb::function_view) gdb/symfile-debug.c:219 (gdb+0xda5b6e) #5 iterate_over_symtabs(char const*, gdb::function_view) gdb/symtab.c:648 (gdb+0xdc441d) #6 lookup_symtab(char const*) gdb/symtab.c:662 (gdb+0xdc4522) #7 classify_name gdb/c-exp.y:3083 (gdb+0x61afec) #8 c_yylex gdb/c-exp.y:3251 (gdb+0x61dd13) #9 c_yyparse() build/gdb/c-exp.c.tmp:1988 (gdb+0x61f07e) #10 c_parse(parser_state*) gdb/c-exp.y:3417 (gdb+0x62d864) #11 language_defn::parser(parser_state*) const gdb/language.c:598 (gdb+0x977245) #12 parse_exp_in_context gdb/parse.c:414 (gdb+0xb10b1b) #13 parse_expression(char const*, innermost_block_tracker*, enum_flags) gdb/parse.c:462 (gdb+0xb1112e) #14 process_print_command_args gdb/printcmd.c:1321 (gdb+0xb4bf8c) #15 print_command_1 gdb/printcmd.c:1335 (gdb+0xb4caaa) #16 print_command gdb/printcmd.c:1468 (gdb+0xb4cdda) #17 do_simple_func gdb/cli/cli-decode.c:95 (gdb+0x65b078) #18 cmd_func(cmd_list_element*, char const*, int) gdb/cli/cli-decode.c:2735 (gdb+0x65ed53) #19 execute_command(char const*, int) gdb/top.c:575 (gdb+0xe3a7ea) #20 catch_command_errors gdb/main.c:518 (gdb+0xa183fd) #21 execute_cmdargs gdb/main.c:617 (gdb+0xa185bf) #22 captured_main_1 gdb/main.c:1289 (gdb+0xa1aad8) #23 captured_main gdb/main.c:1310 (gdb+0xa1b9da) #24 gdb_main(captured_main_args*) gdb/main.c:1339 (gdb+0xa1b9da) #25 main gdb/gdb.c:39 (gdb+0x42506a) Previous read of size 1 at 0x7b200000410d by thread T2: #0 write_gdbindex gdb/dwarf2/index-write.c:1214 (gdb+0x75bb30) #1 write_dwarf_index(dwarf2_per_bfd*, char const*, char const*, char const*, dw_index_kind) gdb/dwarf2/index-write.c:1469 (gdb+0x75f803) #2 index_cache::store(dwarf2_per_bfd*, index_cache_store_context const&) gdb/dwarf2/index-cache.c:173 (gdb+0x755a36) #3 cooked_index::maybe_write_index(dwarf2_per_bfd*, index_cache_store_context const&) gdb/dwarf2/cooked-index.c:642 (gdb+0x71c96d) #4 operator() gdb/dwarf2/cooked-index.c:471 (gdb+0x71c96d) #5 _M_invoke /usr/include/c++/7/bits/std_function.h:316 (gdb+0x71c96d) #6 std::function::operator()() const /usr/include/c++/7/bits/std_function.h:706 (gdb+0x72a57c) #7 void std::__invoke_impl&>(std::__invoke_other, std::function&) /usr/include/c++/7/bits/invoke.h:60 (gdb+0x72a5db) #8 std::__invoke_result&>::type std::__invoke&>(std::function&) /usr/include/c++/7/bits/invoke.h:95 (gdb+0x72a5db) #9 std::__future_base::_Task_state, std::allocator, void ()>::_M_run()::{lambda()#1}::operator()() const /usr/include/c++/7/future:1421 (gdb+0x72a5db) #10 std::__future_base::_Task_setter, std::__future_base::_Result_base::_Deleter>, std::__future_base::_Task_state, std::allocator, void ()>::_M_run()::{lambda()#1}, void>::operator()() const /usr/include/c++/7/future:1362 (gdb+0x72a5db) #11 std::_Function_handler (), std::__future_base::_Task_setter, std::__future_base::_Result_base::_Deleter>, std::__future_base::_Task_state, std::allocator, void ()>::_M_run()::{lambda()#1}, void> >::_M_invoke(std::_Any_data const&) /usr/include/c++/7/bits/std_function.h:302 (gdb+0x72a5db) #12 std::function ()>::operator()() const /usr/include/c++/7/bits/std_function.h:706 (gdb+0x724954) #13 std::__future_base::_State_baseV2::_M_do_set(std::function ()>*, bool*) /usr/include/c++/7/future:561 (gdb+0x724954) #14 void std::__invoke_impl ()>*, bool*), std::__future_base::_State_baseV2*, std::function ()>*, bool*>(std::__invoke_memfun_deref, void (std::__future_base::_State_baseV2::*&&)(std::function ()>*, bool*), std::__future_base::_State_baseV2*&&, std::function ()>*&&, bool*&&) /usr/include/c++/7/bits/invoke.h:73 (gdb+0x72434a) #15 std::__invoke_result ()>*, bool*), std::__future_base::_State_baseV2*, std::function ()>*, bool*>::type std::__invoke ()>*, bool*), std::__future_base::_State_baseV2*, std::function ()>*, bool*>(void (std::__future_base::_State_baseV2::*&&)(std::function ()>*, bool*), std::__future_base::_State_baseV2*&&, std::function ()>*&&, bool*&&) /usr/include/c++/7/bits/invoke.h:95 (gdb+0x72434a) #16 std::call_once ()>*, bool*), std::__future_base::_State_baseV2*, std::function ()>*, bool*>(std::once_flag&, void (std::__future_base::_State_baseV2::*&&)(std::function ()>*, bool*), std::__future_base::_State_baseV2*&&, std::function ()>*&&, bool*&&)::{lambda()#1}::operator()() const /usr/include/c++/7/mutex:672 (gdb+0x72434a) #17 std::call_once ()>*, bool*), std::__future_base::_State_baseV2*, std::function ()>*, bool*>(std::once_flag&, void (std::__future_base::_State_baseV2::*&&)(std::function ()>*, bool*), std::__future_base::_State_baseV2*&&, std::function ()>*&&, bool*&&)::{lambda()#2}::operator()() const /usr/include/c++/7/mutex:677 (gdb+0x72434a) #18 std::call_once ()>*, bool*), std::__future_base::_State_baseV2*, std::function ()>*, bool*>(std::once_flag&, void (std::__future_base::_State_baseV2::*&&)(std::function ()>*, bool*), std::__future_base::_State_baseV2*&&, std::function ()>*&&, bool*&&)::{lambda()#2}::_FUN() /usr/include/c++/7/mutex:677 (gdb+0x72434a) #19 pthread_once (libtsan.so.0+0x4457c) #20 __gthread_once /usr/include/c++/7/x86_64-suse-linux/bits/gthr-default.h:699 (gdb+0x72532b) #21 void std::call_once ()>*, bool*), std::__future_base::_State_baseV2*, std::function ()>*, bool*>(std::once_flag&, void (std::__future_base::_State_baseV2::*&&)(std::function ()>*, bool*), std::__future_base::_State_baseV2*&&, std::function ()>*&&, bool*&&) /usr/include/c++/7/mutex:684 (gdb+0x72532b) #22 std::__future_base::_State_baseV2::_M_set_result(std::function ()>, bool) /usr/include/c++/7/future:401 (gdb+0x174570d) #23 std::__future_base::_Task_state, std::allocator, void ()>::_M_run() /usr/include/c++/7/future:1423 (gdb+0x174570d) #24 std::packaged_task::operator()() /usr/include/c++/7/future:1556 (gdb+0x174570d) #25 gdb::thread_pool::thread_function() gdbsupport/thread-pool.cc:242 (gdb+0x174570d) #26 void std::__invoke_impl(std::__invoke_memfun_deref, void (gdb::thread_pool::*&&)(), gdb::thread_pool*&&) /usr/include/c++/7/bits/invoke.h:73 (gdb+0x17480c0) #27 std::__invoke_result::type std::__invoke(void (gdb::thread_pool::*&&)(), gdb::thread_pool*&&) /usr/include/c++/7/bits/invoke.h:95 (gdb+0x17480c0) #28 decltype (__invoke((_S_declval<0ul>)(), (_S_declval<1ul>)())) std::thread::_Invoker >::_M_invoke<0ul, 1ul>(std::_Index_tuple<0ul, 1ul>) /usr/include/c++/7/thread:234 (gdb+0x17480c0) #29 std::thread::_Invoker >::operator()() /usr/include/c++/7/thread:243 (gdb+0x17480c0) #30 std::thread::_State_impl > >::_M_run() /usr/include/c++/7/thread:186 (gdb+0x17480c0) #31 (libstdc++.so.6+0xdcac2) ... SUMMARY: ThreadSanitizer: data race gdb/dwarf2/read.c:2033 in dw2_get_file_names_reader ... The race happens when issuing the "file $exec" command. The race is between: - a worker thread writing the index cache, and in the process reading dwarf2_per_cu_data::is_debug_type, and - the main thread writing to dwarf2_per_cu_data::files_read. The two bitfields dwarf2_per_cu_data::files_read and dwarf2_per_cu_data::is_debug_type share the same bitfield container. Fix this by making dwarf2_per_cu_data::files_read a packed. Tested on x86_64-linux. PR symtab/30718 Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30718 --- gdb/dwarf2/read.h | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/gdb/dwarf2/read.h b/gdb/dwarf2/read.h index 44bc3ce88a0c..9dfc435e861c 100644 --- a/gdb/dwarf2/read.h +++ b/gdb/dwarf2/read.h @@ -104,10 +104,10 @@ struct dwarf2_per_cu_data is_dwz (false), reading_dwo_directly (false), tu_read (false), - files_read (false), queued (false), m_header_read_in (false), mark (false), + files_read (false), scanned (false) { } @@ -150,10 +150,6 @@ struct dwarf2_per_cu_data This flag is only valid if is_debug_types is true. */ unsigned int tu_read : 1; - /* True if we've tried to read the file table. There will be no - point in trying to read it again next time. */ - bool files_read : 1; - /* Wrap the following in struct packed instead of bitfields to avoid data races when the bitfields end up on the same memory location (per C++ memory model). */ @@ -176,6 +172,10 @@ struct dwarf2_per_cu_data expand_symtabs_matching. */ packed mark; + /* True if we've tried to read the file table. There will be no + point in trying to read it again next time. */ + packed files_read; + private: /* The unit type of this CU. */ std::atomic> m_unit_type {(dwarf_unit_type)0};