[lldb/Target] Add GetStartSymbol method to DynamicLoader plugins (#99673)

Summary:
This patch introduces a new method to the dynamic loader plugin, to
fetch its `start` symbol.

This can be useful to resolve the `start` symbol address for instance.

Signed-off-by: Med Ismail Bennani <[email protected]>

Test Plan: 

Reviewers: 

Subscribers: 

Tasks: 

Tags: 


Differential Revision: https://phabricator.intern.facebook.com/D60251468

Author: medismailben

lldb/include/lldb/Target/DynamicLoader.h

@@ -10,6 +10,7 @@
 #define LLDB_TARGET_DYNAMICLOADER_H
 
 #include "lldb/Core/PluginInterface.h"
+#include "lldb/Symbol/Symbol.h"
 #include "lldb/Utility/FileSpec.h"
 #include "lldb/Utility/Status.h"
 #include "lldb/Utility/UUID.h"
@@ -24,7 +25,6 @@ namespace lldb_private {
 class ModuleList;
 class Process;
 class SectionList;
-class Symbol;
 class SymbolContext;
 class SymbolContextList;
 class Thread;
@@ -329,6 +329,13 @@ class DynamicLoader : public PluginInterface {
   /// safe to call certain APIs or SPIs.
   virtual bool IsFullyInitialized() { return true; }
 
+  /// Return the `start` function \b symbol in the dynamic loader module.
+  /// This is the symbol the process will begin executing with
+  /// `process launch --stop-at-entry`.
+  virtual std::optional<lldb_private::Symbol> GetStartSymbol() {
+    return std::nullopt;
+  }
+
 protected:
   // Utility methods for derived classes
 

lldb/source/Plugins/DynamicLoader/MacOSX-DYLD/DynamicLoaderDarwin.cpp

@@ -609,6 +609,26 @@ void DynamicLoaderDarwin::UpdateDYLDImageInfoFromNewImageInfo(
   }
 }
 
+std::optional<lldb_private::Symbol> DynamicLoaderDarwin::GetStartSymbol() {
+  Log *log = GetLog(LLDBLog::DynamicLoader);
+
+  auto log_err = [log](llvm::StringLiteral err_msg) -> std::nullopt_t {
+    LLDB_LOGV(log, "{}", err_msg);
+    return std::nullopt;
+  };
+
+  ModuleSP dyld_sp = GetDYLDModule();
+  if (!dyld_sp)
+    return log_err("Couldn't retrieve DYLD module. Cannot get `start` symbol.");
+
+  const Symbol *symbol =
+      dyld_sp->FindFirstSymbolWithNameAndType(ConstString("_dyld_start"));
+  if (!symbol)
+    return log_err("Cannot find `start` symbol in DYLD module.");
+
+  return *symbol;
+}
+
 void DynamicLoaderDarwin::SetDYLDModule(lldb::ModuleSP &dyld_module_sp) {
   m_dyld_module_wp = dyld_module_sp;
 }

lldb/source/Plugins/DynamicLoader/MacOSX-DYLD/DynamicLoaderDarwin.h

@@ -67,6 +67,8 @@ class DynamicLoaderDarwin : public lldb_private::DynamicLoader {
   // Clear method for classes derived from this one
   virtual void DoClear() = 0;
 
+  std::optional<lldb_private::Symbol> GetStartSymbol() override;
+
   void SetDYLDModule(lldb::ModuleSP &dyld_module_sp);
 
   lldb::ModuleSP GetDYLDModule();