[Lldb-commits] [lldb] [lldb] Change Module to have a concrete UnwindTable, update (PR #101130)
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Tue Jul 30 15:25:59 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-lldb
Author: Jason Molenda (jasonmolenda)
<details>
<summary>Changes</summary>
Currently a Module has a std::optional<UnwindTable> which is created when the UnwindTable is requested from outside the Module. The idea is to delay its creation until the Module has an ObjectFile initialized, which will have been done by the time we're doing an unwind.
However, Module::GetUnwindTable wasn't doing any locking, so it was possible for two threads to ask for the UnwindTable for the first time, one would be created and returned while another thread would create one, destroy the first in the process of emplacing it. It was an uncommon crash, but it was possible.
Grabbing the Module's mutex would be one way to address it, but when loading ELF binaries, we start creating the SymbolTable on one thread (ObjectFileELF) grabbing the Module's mutex, and then spin up worker threads to parse the individual DWARF compilation units, which then try to also get the UnwindTable and deadlock if they try to get the Module's mutex.
This changes Module to have a concrete UnwindTable as an ivar, and when it adds an ObjectFile or SymbolFileVendor, it will call the Update method on it, which will re-evaluate which sections exist in the ObjectFile/SymbolFile. UnwindTable used to have an Initialize method which set all the sections, and an Update method which would set some of them if they weren't set. I unified these with the Initialize method taking a `force` option to re-initialize the section pointers even if they had been done already before.
This is addressing a rare crash report we've received, and also a failure Adrian spotted on the -fsanitize=address CI bot last week, it's still uncommon with ASAN but it can happen with the standard testsuite.
rdar://128876433
---
Full diff: https://github.com/llvm/llvm-project/pull/101130.diff
4 Files Affected:
- (modified) lldb/include/lldb/Core/Module.h (+3-3)
- (modified) lldb/include/lldb/Symbol/UnwindTable.h (+3-3)
- (modified) lldb/source/Core/Module.cpp (+15-11)
- (modified) lldb/source/Symbol/UnwindTable.cpp (+10-51)
``````````diff
diff --git a/lldb/include/lldb/Core/Module.h b/lldb/include/lldb/Core/Module.h
index 0188057247a68..5589c1c9a350d 100644
--- a/lldb/include/lldb/Core/Module.h
+++ b/lldb/include/lldb/Core/Module.h
@@ -1021,9 +1021,9 @@ class Module : public std::enable_shared_from_this<Module>,
lldb::ObjectFileSP m_objfile_sp; ///< A shared pointer to the object file
/// parser for this module as it may or may
/// not be shared with the SymbolFile
- std::optional<UnwindTable> m_unwind_table; ///< Table of FuncUnwinders
- /// objects created for this
- /// Module's functions
+ UnwindTable m_unwind_table; ///< Table of FuncUnwinders
+ /// objects created for this
+ /// Module's functions
lldb::SymbolVendorUP
m_symfile_up; ///< A pointer to the symbol vendor for this module.
std::vector<lldb::SymbolVendorUP>
diff --git a/lldb/include/lldb/Symbol/UnwindTable.h b/lldb/include/lldb/Symbol/UnwindTable.h
index 26826e5d1b497..bfcf1c3c072d6 100644
--- a/lldb/include/lldb/Symbol/UnwindTable.h
+++ b/lldb/include/lldb/Symbol/UnwindTable.h
@@ -57,9 +57,9 @@ class UnwindTable {
ArchSpec GetArchitecture();
- /// Called after a SymbolFile has been added to a Module to add any new
- /// unwind sections that may now be available.
- void Update();
+ /// Called after an ObjectFile/SymbolFile has been added to a Module to add
+ /// any new unwind sections that may now be available.
+ void ModuleWasUpdated();
private:
void Dump(Stream &s);
diff --git a/lldb/source/Core/Module.cpp b/lldb/source/Core/Module.cpp
index 9c105b3f0e57a..f9d7832254f46 100644
--- a/lldb/source/Core/Module.cpp
+++ b/lldb/source/Core/Module.cpp
@@ -131,7 +131,8 @@ Module *Module::GetAllocatedModuleAtIndex(size_t idx) {
}
Module::Module(const ModuleSpec &module_spec)
- : m_file_has_changed(false), m_first_file_changed_log(false) {
+ : m_unwind_table(*this), m_file_has_changed(false),
+ m_first_file_changed_log(false) {
// Scope for locker below...
{
std::lock_guard<std::recursive_mutex> guard(
@@ -238,7 +239,8 @@ Module::Module(const FileSpec &file_spec, const ArchSpec &arch,
: m_mod_time(FileSystem::Instance().GetModificationTime(file_spec)),
m_arch(arch), m_file(file_spec), m_object_name(object_name),
m_object_offset(object_offset), m_object_mod_time(object_mod_time),
- m_file_has_changed(false), m_first_file_changed_log(false) {
+ m_unwind_table(*this), m_file_has_changed(false),
+ m_first_file_changed_log(false) {
// Scope for locker below...
{
std::lock_guard<std::recursive_mutex> guard(
@@ -254,7 +256,9 @@ Module::Module(const FileSpec &file_spec, const ArchSpec &arch,
m_object_name.AsCString(""), m_object_name.IsEmpty() ? "" : ")");
}
-Module::Module() : m_file_has_changed(false), m_first_file_changed_log(false) {
+Module::Module()
+ : m_unwind_table(*this), m_file_has_changed(false),
+ m_first_file_changed_log(false) {
std::lock_guard<std::recursive_mutex> guard(
GetAllocationModuleCollectionMutex());
GetModuleCollection().push_back(this);
@@ -323,6 +327,8 @@ ObjectFile *Module::GetMemoryObjectFile(const lldb::ProcessSP &process_sp,
// Augment the arch with the target's information in case
// we are unable to extract the os/environment from memory.
m_arch.MergeFrom(process_sp->GetTarget().GetArchitecture());
+
+ m_unwind_table.ModuleWasUpdated();
} else {
error.SetErrorString("unable to find suitable object file plug-in");
}
@@ -1009,8 +1015,7 @@ SymbolFile *Module::GetSymbolFile(bool can_create, Stream *feedback_strm) {
m_symfile_up.reset(
SymbolVendor::FindPlugin(shared_from_this(), feedback_strm));
m_did_load_symfile = true;
- if (m_unwind_table)
- m_unwind_table->Update();
+ m_unwind_table.ModuleWasUpdated();
}
}
}
@@ -1210,6 +1215,8 @@ ObjectFile *Module::GetObjectFile() {
// more specific than the generic COFF architecture, only merge in
// those values that overwrite unspecified unknown values.
m_arch.MergeFrom(m_objfile_sp->GetArchitecture());
+
+ m_unwind_table.ModuleWasUpdated();
} else {
ReportError("failed to load objfile for {0}\nDebugging will be "
"degraded for this module.",
@@ -1240,12 +1247,9 @@ void Module::SectionFileAddressesChanged() {
}
UnwindTable &Module::GetUnwindTable() {
- if (!m_unwind_table) {
- if (!m_symfile_spec)
- SymbolLocator::DownloadSymbolFileAsync(GetUUID());
- m_unwind_table.emplace(*this);
- }
- return *m_unwind_table;
+ if (!m_symfile_spec)
+ SymbolLocator::DownloadSymbolFileAsync(GetUUID());
+ return m_unwind_table;
}
SectionList *Module::GetUnifiedSectionList() {
diff --git a/lldb/source/Symbol/UnwindTable.cpp b/lldb/source/Symbol/UnwindTable.cpp
index 11bedf3d6052e..4dfbb953d0b8a 100644
--- a/lldb/source/Symbol/UnwindTable.cpp
+++ b/lldb/source/Symbol/UnwindTable.cpp
@@ -36,7 +36,6 @@ UnwindTable::UnwindTable(Module &module)
// We can't do some of this initialization when the ObjectFile is running its
// ctor; delay doing it until needed for something.
-
void UnwindTable::Initialize() {
if (m_initialized)
return;
@@ -45,55 +44,13 @@ void UnwindTable::Initialize() {
if (m_initialized) // check again once we've acquired the lock
return;
- m_initialized = true;
- ObjectFile *object_file = m_module.GetObjectFile();
- if (!object_file)
- return;
-
- m_object_file_unwind_up = object_file->CreateCallFrameInfo();
-
- SectionList *sl = m_module.GetSectionList();
- if (!sl)
- return;
-
- SectionSP sect = sl->FindSectionByType(eSectionTypeEHFrame, true);
- if (sect.get()) {
- m_eh_frame_up = std::make_unique<DWARFCallFrameInfo>(
- *object_file, sect, DWARFCallFrameInfo::EH);
- }
-
- sect = sl->FindSectionByType(eSectionTypeDWARFDebugFrame, true);
- if (sect) {
- m_debug_frame_up = std::make_unique<DWARFCallFrameInfo>(
- *object_file, sect, DWARFCallFrameInfo::DWARF);
- }
-
- sect = sl->FindSectionByType(eSectionTypeCompactUnwind, true);
- if (sect) {
- m_compact_unwind_up =
- std::make_unique<CompactUnwindInfo>(*object_file, sect);
- }
-
- sect = sl->FindSectionByType(eSectionTypeARMexidx, true);
- if (sect) {
- SectionSP sect_extab = sl->FindSectionByType(eSectionTypeARMextab, true);
- if (sect_extab.get()) {
- m_arm_unwind_up =
- std::make_unique<ArmUnwindInfo>(*object_file, sect, sect_extab);
- }
- }
-}
-
-void UnwindTable::Update() {
- if (!m_initialized)
- return Initialize();
-
- std::lock_guard<std::mutex> guard(m_mutex);
ObjectFile *object_file = m_module.GetObjectFile();
if (!object_file)
return;
+ m_initialized = true;
+
if (!m_object_file_unwind_up)
m_object_file_unwind_up = object_file->CreateCallFrameInfo();
@@ -102,22 +59,19 @@ void UnwindTable::Update() {
return;
SectionSP sect = sl->FindSectionByType(eSectionTypeEHFrame, true);
- if (!m_eh_frame_up && sect) {
+ if (!m_eh_frame_up && sect)
m_eh_frame_up = std::make_unique<DWARFCallFrameInfo>(
*object_file, sect, DWARFCallFrameInfo::EH);
- }
sect = sl->FindSectionByType(eSectionTypeDWARFDebugFrame, true);
- if (!m_debug_frame_up && sect) {
+ if (!m_debug_frame_up && sect)
m_debug_frame_up = std::make_unique<DWARFCallFrameInfo>(
*object_file, sect, DWARFCallFrameInfo::DWARF);
- }
sect = sl->FindSectionByType(eSectionTypeCompactUnwind, true);
- if (!m_compact_unwind_up && sect) {
+ if (!m_compact_unwind_up && sect)
m_compact_unwind_up =
std::make_unique<CompactUnwindInfo>(*object_file, sect);
- }
sect = sl->FindSectionByType(eSectionTypeARMexidx, true);
if (!m_arm_unwind_up && sect) {
@@ -129,6 +83,11 @@ void UnwindTable::Update() {
}
}
+void UnwindTable::ModuleWasUpdated() {
+ std::lock_guard<std::mutex> guard(m_mutex);
+ m_initialized = false;
+}
+
UnwindTable::~UnwindTable() = default;
std::optional<AddressRange>
``````````
</details>
https://github.com/llvm/llvm-project/pull/101130
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