lldb PlatformDarwinKernel make local filesystem scan lazy

Instead of doing the local filesystem scan for kexts and kernels
when the PlatformDarwinKernel is constructed, delay doing it until
the scan is needed.

Differential Revision: https://reviews.llvm.org/D150621
rdar://109186357

(cherry picked from commit e3227e7)

Author: jasonmolenda

lldb/source/Plugins/Platform/MacOSX/PlatformDarwinKernel.cpp

@@ -234,12 +234,8 @@ PlatformDarwinKernel::PlatformDarwinKernel(
       m_name_to_kext_path_map_without_dsyms(), m_search_directories(),
       m_search_directories_no_recursing(), m_kernel_binaries_with_dsyms(),
       m_kernel_binaries_without_dsyms(), m_kernel_dsyms_no_binaries(),
-      m_kernel_dsyms_yaas(), m_ios_debug_session(is_ios_debug_session)
-
-{
-  CollectKextAndKernelDirectories();
-  SearchForKextsAndKernelsRecursively();
-}
+      m_kernel_dsyms_yaas(), m_ios_debug_session(is_ios_debug_session),
+      m_kext_scan_flag() {}
 
 /// Destructor.
 ///
@@ -248,6 +244,7 @@ PlatformDarwinKernel::PlatformDarwinKernel(
 PlatformDarwinKernel::~PlatformDarwinKernel() = default;
 
 void PlatformDarwinKernel::GetStatus(Stream &strm) {
+  UpdateKextandKernelsLocalScan();
   Platform::GetStatus(strm);
   strm.Printf(" Debug session type: ");
   if (m_ios_debug_session == eLazyBoolYes)
@@ -716,6 +713,13 @@ PlatformDarwinKernel::GetDWARFBinaryInDSYMBundle(FileSpec dsym_bundle) {
   return results;
 }
 
+void PlatformDarwinKernel::UpdateKextandKernelsLocalScan() {
+  std::call_once(m_kext_scan_flag, [this]() {
+    CollectKextAndKernelDirectories();
+    SearchForKextsAndKernelsRecursively();
+  });
+}
+
 Status PlatformDarwinKernel::GetSharedModule(
     const ModuleSpec &module_spec, Process *process, ModuleSP &module_sp,
     const FileSpecList *module_search_paths_ptr,
@@ -796,6 +800,7 @@ Status PlatformDarwinKernel::GetSharedModuleKernel(
     llvm::SmallVectorImpl<ModuleSP> *old_modules, bool *did_create_ptr) {
   Status error;
   module_sp.reset();
+  UpdateKextandKernelsLocalScan();
 
   // First try all kernel binaries that have a dSYM next to them
   for (auto possible_kernel : m_kernel_binaries_with_dsyms) {

lldb/source/Plugins/Platform/MacOSX/PlatformDarwinKernel.h

@@ -157,6 +157,8 @@ class PlatformDarwinKernel : public PlatformDarwin {
   bool LoadPlatformBinaryAndSetup(Process *process, lldb::addr_t addr,
                                   bool notify) override;
 
+  void UpdateKextandKernelsLocalScan();
+
   // Most of the ivars are assembled under FileSystem::EnumerateDirectory calls
   // where the function being called for each file/directory must be static.
   // We'll pass a this pointer as a baton and access the ivars directly.
@@ -193,6 +195,8 @@ class PlatformDarwinKernel : public PlatformDarwin {
 
   LazyBool m_ios_debug_session;
 
+  std::once_flag m_kext_scan_flag;
+
   PlatformDarwinKernel(const PlatformDarwinKernel &) = delete;
   const PlatformDarwinKernel &operator=(const PlatformDarwinKernel &) = delete;
 };