[lldb] Expand background symbol lookup

LLDB has a setting (symbols.enable-background-lookup) that calls dsymForUUID on
a background thread for images as they appear in the current backtrace.
Originally, the laziness of only looking up symbols for images in the
backtrace only existed to bring the number of dsymForUUID calls down to
a manageable number.

Users have requesting the same functionality but blocking. This gives
them the same user experience as enabling dsymForUUID globally, but
without the massive upfront cost of having to download all the images,
the majority of which they'll likely not need.

This patch renames the setting to have a more generic name
(symbols.lazy-lookup) and changes its values from a boolean to an enum.
Users can now specify lazy-lookup as "off", "background" and
"foreground". The default remains "off" although I'll probably change
that in the near future.

Author: JDevlieghere

lldb/include/lldb/Core/ModuleList.h

@@ -47,6 +47,26 @@ class UUID;
 class VariableList;
 struct ModuleFunctionSearchOptions;
 
+static constexpr OptionEnumValueElement g_lazy_lookup_enum_values[] = {
+    {
+        lldb::eLazyLookupOff,
+        "off",
+        "Disable lazy symbol lookup.",
+    },
+    {
+        lldb::eLazyLookupBackground,
+        "background",
+        "Lazily look up symbols in the background without blocking the "
+        "debugger.",
+    },
+    {
+        lldb::eLazyLookupForeground,
+        "foreground",
+        "Lazily look up symbols in the foreground and block the debugger until "
+        "they're found.",
+    },
+};
+
 class ModuleListProperties : public Properties {
   mutable llvm::sys::RWMutex m_symlink_paths_mutex;
   PathMappingList m_symlink_paths;
@@ -60,7 +80,6 @@ class ModuleListProperties : public Properties {
   bool SetClangModulesCachePath(const FileSpec &path);
   bool GetEnableExternalLookup() const;
   bool SetEnableExternalLookup(bool new_value);
-  bool GetEnableBackgroundLookup() const;
   bool GetEnableLLDBIndexCache() const;
   bool SetEnableLLDBIndexCache(bool new_value);
   uint64_t GetLLDBIndexCacheMaxByteSize();
@@ -71,6 +90,8 @@ class ModuleListProperties : public Properties {
 
   bool GetLoadSymbolOnDemand();
 
+  lldb::LazySymbolLookup GetLazySymbolLookup() const;
+
   PathMappingList GetSymlinkMappings() const;
 };
 

lldb/include/lldb/lldb-enumerations.h

@@ -1305,6 +1305,12 @@ enum CompletionType {
   eTerminatorCompletion = (1ul << 27)
 };
 
+enum LazySymbolLookup {
+  eLazyLookupOff = 0,
+  eLazyLookupBackground = 1,
+  eLazyLookupForeground = 2,
+};
+
 } // namespace lldb
 
 #endif // LLDB_LLDB_ENUMERATIONS_H

lldb/source/Core/CoreProperties.td

@@ -5,10 +5,11 @@ let Definition = "modulelist" in {
     Global,
     DefaultTrue,
     Desc<"Control the use of external tools and repositories to locate symbol files. Directories listed in target.debug-file-search-paths and directory of the executable are always checked first for separate debug info files. Then depending on this setting: On macOS, Spotlight would be also used to locate a matching .dSYM bundle based on the UUID of the executable. On NetBSD, directory /usr/libdata/debug would be also searched. On platforms other than NetBSD directory /usr/lib/debug would be also searched. If all other methods fail there may be symbol-locator plugins that, if configured properly, will also attempt to acquire symbols. The debuginfod plugin defaults to the DEGUFINFOD_URLS environment variable which is configurable through the 'plugin.symbol-locator.debuginfod.server_urls' setting.">;
-  def EnableBackgroundLookup: Property<"enable-background-lookup", "Boolean">,
+  def LazySymbolLookup: Property<"lazy-lookup", "Enum">,
     Global,
-    DefaultFalse,
-    Desc<"On macOS, enable calling dsymForUUID (or an equivalent script/binary) in the background to locate symbol files that weren't found.">;
+    DefaultEnumValue<"eLazyLookupOff">,
+    EnumValues<"OptionEnumValues(g_lazy_lookup_enum_values)">,
+    Desc<"On macOS, lazily look up symbols with dsymForUUID (or an equivalent script/binary) as images appear in the current backtrace.">;
   def ClangModulesCachePath: Property<"clang-modules-cache-path", "FileSpec">,
     Global,
     DefaultStringValue<"">,

lldb/source/Core/ModuleList.cpp

@@ -104,10 +104,11 @@ bool ModuleListProperties::SetEnableExternalLookup(bool new_value) {
   return SetPropertyAtIndex(ePropertyEnableExternalLookup, new_value);
 }
 
-bool ModuleListProperties::GetEnableBackgroundLookup() const {
-  const uint32_t idx = ePropertyEnableBackgroundLookup;
-  return GetPropertyAtIndexAs<bool>(
-      idx, g_modulelist_properties[idx].default_uint_value != 0);
+LazySymbolLookup ModuleListProperties::GetLazySymbolLookup() const {
+  const uint32_t idx = ePropertyLazySymbolLookup;
+  return GetPropertyAtIndexAs<lldb::LazySymbolLookup>(
+      idx, static_cast<lldb::LazySymbolLookup>(
+               g_modulelist_properties[idx].default_uint_value));
 }
 
 FileSpec ModuleListProperties::GetClangModulesCachePath() const {

lldb/source/Symbol/SymbolLocator.cpp

@@ -18,12 +18,10 @@ using namespace lldb;
 using namespace lldb_private;
 
 void SymbolLocator::DownloadSymbolFileAsync(const UUID &uuid) {
-  if (!ModuleList::GetGlobalModuleListProperties().GetEnableBackgroundLookup())
-    return;
-
   static llvm::SmallSet<UUID, 8> g_seen_uuids;
   static std::mutex g_mutex;
-  Debugger::GetThreadPool().async([=]() {
+
+  auto lookup = [=]() {
     {
       std::lock_guard<std::mutex> guard(g_mutex);
       if (g_seen_uuids.count(uuid))
@@ -43,5 +41,16 @@ void SymbolLocator::DownloadSymbolFileAsync(const UUID &uuid) {
       return;
 
     Debugger::ReportSymbolChange(module_spec);
-  });
+  };
+
+  switch (ModuleList::GetGlobalModuleListProperties().GetLazySymbolLookup()) {
+  case eLazyLookupOff:
+    break;
+  case eLazyLookupBackground:
+    Debugger::GetThreadPool().async(lookup);
+    break;
+  case eLazyLookupForeground:
+    lookup();
+    break;
+  };
 }