clayborg added a comment.
I had to revert this. There is a deadlock in:
void Module::PreloadSymbols() {
std::lock_guard<std::recursive_mutex> guard(m_mutex);
SymbolFile *sym_file = GetSymbolFile();
if (!sym_file)
return;
// Prime the symbol file first, since it adds symbols to the symbol table.
sym_file->PreloadSymbols();
// Now we can prime the symbol table.
if (Symtab *symtab = sym_file->GetSymtab())
symtab->PreloadSymbols();
}
That happens only when we are using ELF files since they need to be manually
indexed. What happens is:
- Thread #1 calls "sym_file->PreloadSymbols();"
- Thread #2 starts manually indexing the DWARF and tries to load section data
for a DWARF section which has relocations and since Module::PreloadSymbols()
from thread #1 has the lock.
The backtrace can be seen when debugging:
$ /Users/gclayton/Documents/src/llvm/clean/Debug/bin/lldb --no-lldbinit -S
/Users/gclayton/Documents/src/llvm/clean/Debug/tools/lldb/test/Shell/lit-lldb-init
debug_rnglists-dwo.o -o image lookup -v -s lookup_rnglists -o exit
This deadlocks with:
(lldb) bt all
* thread #1, queue = 'com.apple.main-thread', stop reason = signal SIGSTOP
* frame #0: 0x00000001850f4548 libsystem_kernel.dylib`__psynch_cvwait + 8
frame #1: 0x000000018512bdac libsystem_pthread.dylib`_pthread_cond_wait +
1248
frame #2: 0x0000000185085efc
libc++.1.dylib`std::__1::condition_variable::wait(std::__1::unique_lock<std::__1::mutex>&)
+ 28
frame #3: 0x0000000104ee97a8 LLDB`void
std::__1::condition_variable::wait<llvm::ThreadPool::wait()::$_1>(this=0x000000016d3b03f0,
__lk=0x000000016d3aff58, __pred=(anonymous class) @ 0x000000016d3aff28)::$_1)
at __mutex_base:409:9
frame #4: 0x0000000104ee9728
LLDB`llvm::ThreadPool::wait(this=0x000000016d3b0338) at ThreadPool.cpp:72:23
frame #5: 0x0000000104b97d54
LLDB`lldb_private::ManualDWARFIndex::Index(this=0x00000001302129b0) at
ManualDWARFIndex.cpp:109:8
frame #6: 0x0000000104b0ef98
LLDB`lldb_private::ManualDWARFIndex::Preload(this=0x00000001302129b0) at
ManualDWARFIndex.h:27:29
frame #7: 0x0000000104bb5f1c
LLDB`SymbolFileDWARF::PreloadSymbols(this=0x0000000130815400) at
SymbolFileDWARF.cpp:2071:12
frame #8: 0x0000000103c60dcc
LLDB`lldb_private::Module::PreloadSymbols(this=0x000000013020d238) at
Module.cpp:1383:13
frame #9: 0x0000000104266f44
LLDB`lldb_private::TargetList::CreateTargetInternal(debugger=0x000000013302d200,
user_exe_path=(Data = "debug_rnglists-dwo.o", Length = 20),
specified_arch=0x000000016d3b1478, load_dependent_files=eLoadDependentsDefault,
platform_sp=std::__1::shared_ptr<lldb_private::Platform>::element_type @
0x0000000130705b70 strong=7 weak=1,
target_sp=std::__1::shared_ptr<lldb_private::Target>::element_type @
0x0000000130811600 strong=1 weak=2) at TargetList.cpp:371:24
frame #10: 0x0000000104266648
LLDB`lldb_private::TargetList::CreateTargetInternal(debugger=0x000000013302d200,
user_exe_path=(Data = "debug_rnglists-dwo.o", Length = 20), triple_str=(Data =
"", Length = 0), load_dependent_files=eLoadDependentsDefault,
platform_options=0x0000000133044dc0,
target_sp=std::__1::shared_ptr<lldb_private::Target>::element_type @
0x0000000130811600 strong=1 weak=2) at TargetList.cpp:280:10
frame #11: 0x0000000104265ae0
LLDB`lldb_private::TargetList::CreateTarget(this=0x000000013302d2d0,
debugger=0x000000013302d200, user_exe_path=(Data = "debug_rnglists-dwo.o",
Length = 20), triple_str=(Data = "", Length = 0),
load_dependent_files=eLoadDependentsDefault,
platform_options=0x0000000133044dc0,
target_sp=std::__1::shared_ptr<lldb_private::Target>::element_type @
0x0000000130811600 strong=1 weak=2) at TargetList.cpp:52:17
frame #12: 0x0000000107d2d2a8
LLDB`CommandObjectTargetCreate::DoExecute(this=0x0000000133044c00,
command=0x000000016d3b22a0, result=0x000000016d3b28c0) at
CommandObjectTarget.cpp:314:45
frame #13: 0x0000000103efc228
LLDB`lldb_private::CommandObjectParsed::Execute(this=0x0000000133044c00,
args_string="\"debug_rnglists-dwo.o\"", result=0x000000016d3b28c0) at
CommandObject.cpp:995:19
frame #14: 0x0000000103ebd234
LLDB`lldb_private::CommandInterpreter::HandleCommand(this=0x0000000132834c90,
command_line="target create \"debug_rnglists-dwo.o\"",
lazy_add_to_history=eLazyBoolCalculate, result=0x000000016d3b28c0) at
CommandInterpreter.cpp:1971:14
frame #15: 0x0000000103ec17fc
LLDB`lldb_private::CommandInterpreter::IOHandlerInputComplete(this=0x0000000132834c90,
io_handler=0x0000000130508c18, line="target create \"debug_rnglists-dwo.o\"")
at CommandInterpreter.cpp:3021:3
frame #16: 0x0000000103bffcd8
LLDB`lldb_private::IOHandlerEditline::Run(this=0x0000000130508c18) at
IOHandler.cpp:576:22
frame #17: 0x0000000103b8fbb8
LLDB`lldb_private::Debugger::RunIOHandlers(this=0x000000013302d200) at
Debugger.cpp:877:16
frame #18: 0x0000000103ec2eac
LLDB`lldb_private::CommandInterpreter::RunCommandInterpreter(this=0x0000000132834c90,
options=0x00000001305085a0) at CommandInterpreter.cpp:3267:16
frame #19: 0x000000010349d85c
LLDB`lldb::SBDebugger::RunCommandInterpreter(this=0x000000016d3b31e0,
options=0x000000016d3b2ec0) at SBDebugger.cpp:1267:14
frame #20: 0x0000000102a50da0
lldb`Driver::MainLoop(this=0x000000016d3b31c0) at Driver.cpp:635:20
frame #21: 0x0000000102a51a60 lldb`main(argc=9, argv=0x000000016d3b3720)
at Driver.cpp:965:26
frame #22: 0x0000000185149430 libdyld.dylib`start + 4
thread #2, name = 'lldb.debugger.event-handler'
frame #0: 0x00000001850f4548 libsystem_kernel.dylib`__psynch_cvwait + 8
frame #1: 0x000000018512bdac libsystem_pthread.dylib`_pthread_cond_wait +
1248
frame #2: 0x0000000185085efc
libc++.1.dylib`std::__1::condition_variable::wait(std::__1::unique_lock<std::__1::mutex>&)
+ 28
frame #3: 0x000000010435286c
LLDB`lldb_private::Listener::GetEventInternal(this=0x0000000132834b50,
timeout=0x000000016dbbae58, broadcaster=0x0000000000000000,
broadcaster_names=0x0000000000000000, num_broadcaster_names=0,
event_type_mask=0, event_sp=nullptr) at Listener.cpp:364:28
frame #4: 0x0000000104352cd0
LLDB`lldb_private::Listener::GetEvent(this=0x0000000132834b50,
event_sp=nullptr, timeout=0x000000016dbbae58) at Listener.cpp:399:10
frame #5: 0x0000000103b930a0
LLDB`lldb_private::Debugger::DefaultEventHandler(this=0x000000013302d200) at
Debugger.cpp:1510:22
frame #6: 0x0000000103b933cc
LLDB`lldb_private::Debugger::EventHandlerThread(arg=0x000000013302d200) at
Debugger.cpp:1563:22
frame #7: 0x0000000103e3060c
LLDB`lldb_private::HostNativeThreadBase::ThreadCreateTrampoline(arg=0x0000000130508780)
at HostNativeThreadBase.cpp:65:10
frame #8: 0x00000001081c90f0
LLDB`lldb_private::HostThreadMacOSX::ThreadCreateTrampoline(arg=0x0000000130508780)
at HostThreadMacOSX.mm:67:10
frame #9: 0x000000018512b878 libsystem_pthread.dylib`_pthread_start + 320
thread #3
frame #0: 0x00000001850f3a48 libsystem_kernel.dylib`__psynch_mutexwait + 8
frame #1: 0x0000000185128918
libsystem_pthread.dylib`_pthread_mutex_firstfit_lock_wait + 88
frame #2: 0x0000000185126244
libsystem_pthread.dylib`_pthread_mutex_firstfit_lock_slow + 232
frame #3: 0x00000001850b8c88
libc++.1.dylib`std::__1::recursive_mutex::lock() + 16
frame #4: 0x000000010401a354
LLDB`std::__1::lock_guard<std::__1::recursive_mutex>::lock_guard(this=0x000000016e3c6080,
__m=0x000000013020d250) at __mutex_base:91:27
frame #5: 0x0000000104017a40
LLDB`std::__1::lock_guard<std::__1::recursive_mutex>::lock_guard(this=0x000000016e3c6080,
__m=0x000000013020d250) at __mutex_base:91:21
frame #6: 0x0000000104016ef8
LLDB`lldb_private::ObjectFile::GetSymtab(this=0x0000000130706470) at
ObjectFile.cpp:735:43
frame #7: 0x0000000104771f1c
LLDB`ObjectFileELF::RelocateSection(this=0x0000000130706470,
section=0x0000000130706e10) at ObjectFileELF.cpp:2852:56
frame #8: 0x000000010401771c
LLDB`lldb_private::ObjectFile::ReadSectionData(this=0x0000000130706470,
section=0x0000000130706e10, section_data=0x000000016e3c6538) at
ObjectFile.cpp:527:5
frame #9: 0x0000000104773eb8
LLDB`ObjectFileELF::ReadSectionData(this=0x0000000130706470,
section=0x0000000130706e10, section_data=0x000000016e3c6538) at
ObjectFileELF.cpp:3317:31
frame #10: 0x0000000103cd0210
LLDB`lldb_private::Section::GetSectionData(this=0x0000000130706e10,
section_data=0x000000016e3c6538) at Section.cpp:395:24
frame #11: 0x0000000104b4a648
LLDB`LoadSection(section_list=0x0000000130706200,
section_type=eSectionTypeDWARFDebugInfoDwo) at DWARFContext.cpp:26:15
frame #12: 0x0000000104b4a4f0
LLDB`lldb_private::DWARFContext::LoadOrGetSection(this=0x000000016e3c67a0)::$_0::operator()()
const at DWARFContext.cpp:36:19
frame #13: 0x0000000104b4a444
LLDB`decltype(__f=0x000000016e3c67a0)::$_0>(fp)())
std::__1::__invoke<lldb_private::DWARFContext::LoadOrGetSection(llvm::Optional<lldb::SectionType>,
llvm::Optional<lldb::SectionType>,
lldb_private::DWARFContext::SectionData&)::$_0>(lldb_private::DWARFContext::LoadOrGetSection(llvm::Optional<lldb::SectionType>,
llvm::Optional<lldb::SectionType>,
lldb_private::DWARFContext::SectionData&)::$_0&&) at type_traits:3747:1
frame #14: 0x0000000104b4a41c LLDB`void
std::__1::__call_once_param<std::__1::tuple<lldb_private::DWARFContext::LoadOrGetSection(llvm::Optional<lldb::SectionType>,
llvm::Optional<lldb::SectionType>,
lldb_private::DWARFContext::SectionData&)::$_0&&>
>::__execute<>(this=0x000000016e3c6740, (null)=__tuple_indices<> @
0x000000016e3c669f) at mutex:629:9
frame #15: 0x0000000104b4a3ec
LLDB`std::__1::__call_once_param<std::__1::tuple<lldb_private::DWARFContext::LoadOrGetSection(llvm::Optional<lldb::SectionType>,
llvm::Optional<lldb::SectionType>,
lldb_private::DWARFContext::SectionData&)::$_0&&>
>::operator(this=0x000000016e3c6740)() at mutex:621:9
frame #16: 0x0000000104b4a2b8 LLDB`void
std::__1::__call_once_proxy<std::__1::tuple<lldb_private::DWARFContext::LoadOrGetSection(llvm::Optional<lldb::SectionType>,
llvm::Optional<lldb::SectionType>,
lldb_private::DWARFContext::SectionData&)::$_0&&> >(__vp=0x000000016e3c6740) at
mutex:657:5
frame #17: 0x00000001850b92b0
libc++.1.dylib`std::__1::__call_once(unsigned long volatile&, void*, void
(*)(void*)) + 180
frame #18: 0x0000000104b4a1f0 LLDB`void
std::__1::call_once<lldb_private::DWARFContext::LoadOrGetSection(llvm::Optional<lldb::SectionType>,
llvm::Optional<lldb::SectionType>,
lldb_private::DWARFContext::SectionData&)::$_0>(__flag=0x000000013200d1d0,
__func=0x000000016e3c67a0)::$_0&&) at mutex:675:9
frame #19: 0x0000000104b472b8 LLDB`void
llvm::call_once<lldb_private::DWARFContext::LoadOrGetSection(llvm::Optional<lldb::SectionType>,
llvm::Optional<lldb::SectionType>,
lldb_private::DWARFContext::SectionData&)::$_0>(flag=0x000000013200d1d0,
F=0x000000016e3c67a0)::$_0&&) at Threading.h:92:5
frame #20: 0x0000000104b47274
LLDB`lldb_private::DWARFContext::LoadOrGetSection(this=0x000000013200d0b8,
main_section_type=Optional<lldb::SectionType> @ 0x000000016e3c67d8,
dwo_section_type=Optional<lldb::SectionType> @ 0x000000016e3c67d0,
data=0x000000013200d1d0) at DWARFContext.cpp:34:3
frame #21: 0x0000000104b47558
LLDB`lldb_private::DWARFContext::getOrLoadDebugInfoData(this=0x000000013200d0b8)
at DWARFContext.cpp:69:10
frame #22: 0x0000000104b5b3d8
LLDB`DWARFDebugInfo::ParseUnitsFor(this=0x00000001307068f0, section=DebugInfo)
at DWARFDebugInfo.cpp:74:45
frame #23: 0x0000000104b63980
LLDB`DWARFDebugInfo::ParseUnitHeadersIfNeeded(this=0x000000016e3c6a80)::$_0::operator()()
const at DWARFDebugInfo.cpp:100:5
frame #24: 0x0000000104b63918
LLDB`decltype(__f=0x000000016e3c6a80)::$_0>(fp)())
std::__1::__invoke<DWARFDebugInfo::ParseUnitHeadersIfNeeded()::$_0>(DWARFDebugInfo::ParseUnitHeadersIfNeeded()::$_0&&)
at type_traits:3747:1
frame #25: 0x0000000104b638f0 LLDB`void
std::__1::__call_once_param<std::__1::tuple<DWARFDebugInfo::ParseUnitHeadersIfNeeded()::$_0&&>
>::__execute<>(this=0x000000016e3c6a20, (null)=__tuple_indices<> @
0x000000016e3c697f) at mutex:629:9
frame #26: 0x0000000104b638c0
LLDB`std::__1::__call_once_param<std::__1::tuple<DWARFDebugInfo::ParseUnitHeadersIfNeeded()::$_0&&>
>::operator(this=0x000000016e3c6a20)() at mutex:621:9
frame #27: 0x0000000104b6378c LLDB`void
std::__1::__call_once_proxy<std::__1::tuple<DWARFDebugInfo::ParseUnitHeadersIfNeeded()::$_0&&>
>(__vp=0x000000016e3c6a20) at mutex:657:5
frame #28: 0x00000001850b92b0
libc++.1.dylib`std::__1::__call_once(unsigned long volatile&, void*, void
(*)(void*)) + 180
frame #29: 0x0000000104b636c4 LLDB`void
std::__1::call_once<DWARFDebugInfo::ParseUnitHeadersIfNeeded()::$_0>(__flag=0x0000000130706900,
__func=0x000000016e3c6a80)::$_0&&) at mutex:675:9
frame #30: 0x0000000104b5b9c0 LLDB`void
llvm::call_once<DWARFDebugInfo::ParseUnitHeadersIfNeeded()::$_0>(flag=0x0000000130706900,
F=0x000000016e3c6a80)::$_0&&) at Threading.h:92:5
frame #31: 0x0000000104b5b984
LLDB`DWARFDebugInfo::ParseUnitHeadersIfNeeded(this=0x00000001307068f0) at
DWARFDebugInfo.cpp:99:3
frame #32: 0x0000000104b5c048
LLDB`DWARFDebugInfo::ContainsTypeUnits(this=0x00000001307068f0) at
DWARFDebugInfo.cpp:173:3
frame #33: 0x0000000104bff524
LLDB`SymbolFileDWARFDwo::FindSingleCompileUnit(this=0x000000013200d018) at
SymbolFileDWARFDwo.cpp:62:19
frame #34: 0x0000000104bff48c
LLDB`SymbolFileDWARFDwo::GetDWOCompileUnitForHash(this=0x000000013200d018,
hash=16045690984229367821) at SymbolFileDWARFDwo.cpp:49:26
frame #35: 0x0000000104b7ce44
LLDB`DWARFUnit::ExtractUnitDIEIfNeeded(this=0x000000013081e400) at
DWARFUnit.cpp:84:40
frame #36: 0x0000000104b804a4
LLDB`DWARFUnit::GetDwoSymbolFile(this=0x000000013081e400) at DWARFUnit.cpp:817:3
frame #37: 0x0000000104b98538
LLDB`lldb_private::ManualDWARFIndex::IndexUnit(this=0x00000001302129b0,
unit=0x000000013081e400, dwp=0x0000000000000000, set=0x0000000130213240) at
ManualDWARFIndex.cpp:144:50
frame #38: 0x0000000104ba2354
LLDB`lldb_private::ManualDWARFIndex::Index(this=0x00000001303047c8,
cu_idx=0)::$_1::operator()(unsigned long) const at ManualDWARFIndex.cpp:80:5
frame #39: 0x0000000104ba22e0 LLDB`decltype(__f=0x00000001303047c8,
__args=0x00000001303047f0)::$_1&>(fp)(std::__1::forward<unsigned long&>(fp0)))
std::__1::__invoke<lldb_private::ManualDWARFIndex::Index()::$_1&, unsigned
long&>(lldb_private::ManualDWARFIndex::Index()::$_1&, unsigned long&) at
type_traits:3747:1
frame #40: 0x0000000104ba229c
LLDB`std::__1::__bind_return<lldb_private::ManualDWARFIndex::Index()::$_1,
std::__1::tuple<unsigned long>, std::__1::tuple<>,
__is_valid_bind_return<lldb_private::ManualDWARFIndex::Index()::$_1,
std::__1::tuple<unsigned long>, std::__1::tuple<> >::value>::type
std::__1::__apply_functor<lldb_private::ManualDWARFIndex::Index(__f=0x00000001303047c8,
__bound_args=size=1, (null)=__tuple_indices<0> @ 0x000000016e3c6d5f,
__args=size=0)::$_1, std::__1::tuple<unsigned long>, 0ul, std::__1::tuple<>
>(lldb_private::ManualDWARFIndex::Index()::$_1&, std::__1::tuple<unsigned
long>&, std::__1::__tuple_indices<0ul>, std::__1::tuple<>&&) at
functional:2852:12
frame #41: 0x0000000104ba2254
LLDB`std::__1::__bind_return<lldb_private::ManualDWARFIndex::Index()::$_1,
std::__1::tuple<unsigned long>, std::__1::tuple<>,
__is_valid_bind_return<lldb_private::ManualDWARFIndex::Index()::$_1,
std::__1::tuple<unsigned long>, std::__1::tuple<> >::value>::type
std::__1::__bind<lldb_private::ManualDWARFIndex::Index(this=0x00000001303047c8)::$_1&,
unsigned long&>::operator()<>() at functional:2885:20
frame #42: 0x0000000104ba2210
LLDB`decltype(__f=0x00000001303047c8)::$_1&, unsigned long&>&>(fp)())
std::__1::__invoke<std::__1::__bind<lldb_private::ManualDWARFIndex::Index()::$_1&,
unsigned
long&>&>(std::__1::__bind<lldb_private::ManualDWARFIndex::Index()::$_1&,
unsigned long&>&) at type_traits:3747:1
frame #43: 0x0000000104ba21c4 LLDB`void
std::__1::__invoke_void_return_wrapper<void>::__call<std::__1::__bind<lldb_private::ManualDWARFIndex::Index(__args=0x00000001303047c8)::$_1&,
unsigned
long&>&>(std::__1::__bind<lldb_private::ManualDWARFIndex::Index()::$_1&,
unsigned long&>&) at __functional_base:348:9
frame #44: 0x0000000104ba219c
LLDB`std::__1::__function::__alloc_func<std::__1::__bind<lldb_private::ManualDWARFIndex::Index()::$_1&,
unsigned long&>,
std::__1::allocator<std::__1::__bind<lldb_private::ManualDWARFIndex::Index()::$_1&,
unsigned long&> >, void ()>::operator(this=0x00000001303047c8)() at
functional:1553:16
frame #45: 0x0000000104ba1054
LLDB`std::__1::__function::__func<std::__1::__bind<lldb_private::ManualDWARFIndex::Index()::$_1&,
unsigned long&>,
std::__1::allocator<std::__1::__bind<lldb_private::ManualDWARFIndex::Index()::$_1&,
unsigned long&> >, void ()>::operator(this=0x00000001303047c0)() at
functional:1727:12
frame #46: 0x0000000103f4f47c
LLDB`std::__1::__function::__value_func<void
()>::operator(this=0x0000000130304898)() const at functional:1880:16
frame #47: 0x0000000103f4f414 LLDB`std::__1::function<void
()>::operator(this=0x0000000130304898)() const at functional:2555:12
frame #48: 0x0000000104eee758
LLDB`decltype(__f=0x0000000130304898)>&>(fp)())
std::__1::__invoke<std::__1::function<void ()>&>(std::__1::function<void ()>&)
at type_traits:3747:1
frame #49: 0x0000000104eee288
LLDB`std::__1::__packaged_task_func<std::__1::function<void ()>,
std::__1::allocator<std::__1::function<void ()> >, void
()>::operator(this=0x0000000130304890)() at future:1683:12
frame #50: 0x0000000104eed45c
LLDB`std::__1::__packaged_task_function<void
()>::operator(this=0x000000016e3c6f20)() const at future:1865:12
frame #51: 0x0000000104eecc58 LLDB`std::__1::packaged_task<void
()>::operator(this=0x000000016e3c6f20)() at future:2085:9
frame #52: 0x0000000104eeca24
LLDB`llvm::ThreadPool::ThreadPool(this=0x00000001302128c0)::$_0::operator()()
const at ThreadPool.cpp:51:9
frame #53: 0x0000000104eec900 LLDB`void
llvm::thread::Apply<llvm::ThreadPool::ThreadPool(llvm::ThreadPoolStrategy)::$_0>(Callee=size=1,
(null)=std::__1::index_sequence<> @ 0x000000016e3c6f6f)::$_0>&,
std::__1::integer_sequence<unsigned long>) at thread.h:42:5
frame #54: 0x0000000104eec8cc LLDB`void
llvm::thread::GenericThreadProxy<std::__1::tuple<llvm::ThreadPool::ThreadPool(llvm::ThreadPoolStrategy)::$_0>
>(Ptr=0x00000001302128c0) at thread.h:50:5
frame #55: 0x0000000104eec5bc LLDB`void*
llvm::thread::ThreadProxy<std::__1::tuple<llvm::ThreadPool::ThreadPool(llvm::ThreadPoolStrategy)::$_0>
>(Ptr=0x00000001302128c0) at thread.h:60:5
frame #56: 0x000000018512b878 libsystem_pthread.dylib`_pthread_start + 320
The issue is the ObjectFileELF::GetSymtab() used to _not_ take the module lock,
which is really bad. With this new patch is did take the module lock. So we had
very dangerous multi-threading issues before with ObjectFileELF::GetSymtab()
not being threadsafe which could explain flakiness.
The main issue is how to fix this. @labath: let me know if you have any ideas
on how to fix this. We are asking the symbol file to pre-load the symbols
first, and _then_ asking the symbol table to preload itself. Do you remember
why? The comment "Prime the symbol file first, since it adds symbols to the
symbol table" but the SymbolFile::PreloadSymbols() doesn't seem to do that
anymore. Maybe this was changed? I see the symbol file can add symbols via
SymbolFile::AddSymbols() as seen in:
Symtab *SymbolFile::GetSymtab() {
std::lock_guard<std::recursive_mutex> guard(GetModuleMutex());
if (m_symtab)
return m_symtab;
// Fetch the symtab from the main object file.
m_symtab = GetMainObjectFile()->GetSymtab();
// Then add our symbols to it.
if (m_symtab)
AddSymbols(*m_symtab);
return m_symtab;
}
So one solution is to load the normal symbol table first in
Module::PreloadSymbols():
void Module::PreloadSymbols() {
std::lock_guard<std::recursive_mutex> guard(m_mutex);
SymbolFile *sym_file = GetSymbolFile();
if (!sym_file)
return;
// Load the symbol table first so it can be available to any thread without
a lock
if (Symtab *symtab = sym_file->GetSymtab())
symtab->PreloadSymbols();
// Now let the symbol file preload its symbols
sym_file->PreloadSymbols();
}
Then we would need to modify the ObjectFile::GetSymtab() to be able to check
m_symtab_up without taking the module lock:
Symtab *ObjectFile::GetSymtab() {
// We don't need to take the module lock if the symbol table pointer is
// already set in the std::unique_ptr since it is thread safe for access.
This
// prevents deadlocks where the symbol table has already been parsed and
// someone has the module lock acquired and another thread spins up to do
// something that requires the symbol table. This currently happens in the
// manual DWARF indexing where it will spin up a thread to index the DWARF
and
// that thread might ask for the symbol table in
// ObjectFileELF::RelocateSection() which requires the symbol table and
causes
// a deadlock.
if (auto symtab = m_symtab_up.get())
return symtab;
ModuleSP module_sp(GetModule());
if (module_sp) {
std::lock_guard<std::recursive_mutex> guard(module_sp->GetMutex());
// Check the unique pointer again in case two threads made it to the above
// lock guard and one thread actually acquired the lock first and was
// populating the symbol table. By the time we get to this line of code
// the symbol table will either already be parsed or we need to parse it.
// Here we detect if the symbol table was parsed while the lock was held
// on this thread.
if (auto symtab = m_symtab_up.get())
return symtab;
// We haven't parse the symbol table yet.
ElapsedTime elapsed(module_sp->GetSymtabParseTime());
// Store the symbol table in a local unique pointer until the symbol table
// has been parsed, and then store the value into m_symtab_up.
auto symtab_up = std::make_unique<Symtab>(this);
std::lock_guard<std::recursive_mutex> symtab_guard(
symtab_up->GetMutex());
ParseSymtab(*symtab_up);
symtab_up->Finalize();
m_symtab_up = std::move(symtab_up);
}
return m_symtab_up.get();
}
Any input would be appreciated!
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D113965/new/
https://reviews.llvm.org/D113965
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