[lldb] [darwin kernel debug] When looking for a Darwin kernel symbol file, call GetSharedModules before DownloadObjectAndSymbolFile

[jasonmolenda]

Summary

ModuleList::GetSharedModule will call in to the DebugSymbols framework and may be able to find a file on the local system by Spotlight search, or by using the Platform's override of GetSharedModule, and may be faster than calling Symbols::DownloadObjectAndSymbolFile which calls out to an external program and is likely to do a network filesystem or download of the binary/symbol file.

A small perf improvement, NFC. This is very much jason code, not really looking for a review of this one.

[JDevlieghere]

LGTM

[jasonmolenda]

Rebase patch on current top of tree sources.

lldb/source/Plugins/DynamicLoader/Darwin-Kernel/DynamicLoaderDarwinKernel.cpp

if (!m_module_sp) {
     m_module_sp = target_images.FindModule(m_uuid);
 
     // Search for the kext on the local filesystem via the UUID
     if (!m_module_sp && m_uuid.IsValid()) {
       ModuleSpec module_spec;
       module_spec.GetUUID() = m_uuid;
       module_spec.GetArchitecture() = target.GetArchitecture();
 
-      // For the kernel, we really do need an on-disk file copy of the binary
-      // to do anything useful. This will force a call to dsymForUUID if it
-      // exists, instead of depending on the DebugSymbols preferences being
-      // set.
-      Status kernel_search_error;
-      if (IsKernel()) {
-        if (Symbols::DownloadObjectAndSymbolFile(module_spec,
-                                                 kernel_search_error, true)) {
-          if (FileSystem::Instance().Exists(module_spec.GetFileSpec())) {
-            m_module_sp = std::make_shared<Module>(module_spec.GetFileSpec(),
-                                                   target.GetArchitecture());
-          }
-        }
-      }
-
       // If the current platform is PlatformDarwinKernel, create a ModuleSpec
       // with the filename set to be the bundle ID for this kext, e.g.
       // "com.apple.filesystems.msdosfs", and ask the platform to find it.
       // PlatformDarwinKernel does a special scan for kexts on the local
       // system.
       PlatformSP platform_sp(target.GetPlatform());
-      if (!m_module_sp && platform_sp) {
+      if (platform_sp) {
         static ConstString g_platform_name(
             PlatformDarwinKernel::GetPluginNameStatic());
         if (platform_sp->GetPluginName() == g_platform_name.GetStringRef()) {
           ModuleSpec kext_bundle_module_spec(module_spec);
           FileSpec kext_filespec(m_name.c_str());
           FileSpecList search_paths = target.GetExecutableSearchPaths();
           kext_bundle_module_spec.GetFileSpec() = kext_filespec;
           platform_sp->GetSharedModule(kext_bundle_module_spec, process,
                                        m_module_sp, &search_paths, nullptr,
                                        nullptr);
         }
       }
 
       // Ask the Target to find this file on the local system, if possible.
       // This will search in the list of currently-loaded files, look in the
       // standard search paths on the system, and on a Mac it will try calling
       // the DebugSymbols framework with the UUID to find the binary via its
       // search methods.
       if (!m_module_sp) {
         m_module_sp = target.GetOrCreateModule(module_spec, true /* notify */);
       }
 
+      // For the kernel, we really do need an on-disk file copy of the binary
+      // to do anything useful. This will force a call to dsymForUUID if it
+      // exists, instead of depending on the DebugSymbols preferences being
+      // set.
+      Status kernel_search_error;
+      if (IsKernel() &&
+          (!m_module_sp || !m_module_sp->GetSymbolFileFileSpec())) {
+        if (Symbols::DownloadObjectAndSymbolFile(module_spec,
+                                                 kernel_search_error, true)) {
+          if (FileSystem::Instance().Exists(module_spec.GetFileSpec())) {
+            m_module_sp = std::make_shared<Module>(module_spec.GetFileSpec(),
+                                                   target.GetArchitecture());
+          }
+        }
+      }
+
       if (IsKernel() && !m_module_sp) {
         Stream &s = target.GetDebugger().GetErrorStream();
         s.Printf("WARNING: Unable to locate kernel binary on the debugger "
                  "system.\n");
         if (kernel_search_error.Fail() && kernel_search_error.AsCString("") &&
             kernel_search_error.AsCString("")[0] != '\0') {
           s << kernel_search_error.AsCString();
         }