[Lldb-commits] [lldb] [lldb/Target] Add GetStartSymbol method to DynamicLoader plugins (PR #99673)

[Med Ismail Bennani via lldb-commits]

https://github.com/medismailben updated https://github.com/llvm/llvm-project/pull/99673

>From 16ef7297eef25d329631fd62d126bf7a7be24c4d Mon Sep 17 00:00:00 2001
From: Med Ismail Bennani <ismail at bennani.ma>
Date: Fri, 19 Jul 2024 11:08:39 -0700
Subject: [PATCH] [lldb/Target] Add GetStartSymbol method to DynamicLoader
 plugins

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 <ismail at bennani.ma>
---
 lldb/include/lldb/Target/DynamicLoader.h      | 10 +++++++++-
 .../MacOSX-DYLD/DynamicLoaderDarwin.cpp       | 20 +++++++++++++++++++
 .../MacOSX-DYLD/DynamicLoaderDarwin.h         |  2 ++
 3 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/lldb/include/lldb/Target/DynamicLoader.h b/lldb/include/lldb/Target/DynamicLoader.h
index e508d192d2759..fd3b3924c2725 100644
--- a/lldb/include/lldb/Target/DynamicLoader.h
+++ b/lldb/include/lldb/Target/DynamicLoader.h
@@ -10,9 +10,11 @@
 #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"
+#include "lldb/Utility/UnimplementedError.h"
 #include "lldb/lldb-defines.h"
 #include "lldb/lldb-forward.h"
 #include "lldb/lldb-private-enumerations.h"
@@ -24,7 +26,6 @@ namespace lldb_private {
 class ModuleList;
 class Process;
 class SectionList;
-class Symbol;
 class SymbolContext;
 class SymbolContextList;
 class Thread;
@@ -329,6 +330,13 @@ 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
 
diff --git a/lldb/source/Plugins/DynamicLoader/MacOSX-DYLD/DynamicLoaderDarwin.cpp b/lldb/source/Plugins/DynamicLoader/MacOSX-DYLD/DynamicLoaderDarwin.cpp
index 0e17d57fa9c4f..5c6331735bde8 100644
--- a/lldb/source/Plugins/DynamicLoader/MacOSX-DYLD/DynamicLoaderDarwin.cpp
+++ b/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;
 }
diff --git a/lldb/source/Plugins/DynamicLoader/MacOSX-DYLD/DynamicLoaderDarwin.h b/lldb/source/Plugins/DynamicLoader/MacOSX-DYLD/DynamicLoaderDarwin.h
index 8f9a29c94173f..4ac55fdf6f3af 100644
--- a/lldb/source/Plugins/DynamicLoader/MacOSX-DYLD/DynamicLoaderDarwin.h
+++ b/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();