[lldb] add stop-at-user-entry option to process launch (#67019)

## Description
This pull request adds a new `stop-at-user-entry` option to LLDB
`process launch` command, allowing users to launch a process and pause
execution at the entry point of the program (for C-based languages,
`main` function).

## Motivation
This option provides a convenient way to begin debugging a program by
launching it and breaking at the desired entry point.

## Changes Made
- Added `stop-at-user-entry` option to `Options.td` and the
corresponding case in `CommandOptionsProcessLaunch.cpp` (short option is
'm')
- Implemented `GetUserEntryPointName` method in the Language plugins
available at the moment.
- Declared the `CreateBreakpointAtUserEntry` method in the Target API.
- Create Shell test for the command
`command-process-launch-user-entry.test`.

## Usage
`process launch --stop-at-user-entry` or `process launch -m` launches
the process and pauses execution at the entry point of the program.

lldb/include/lldb/Target/Language.h

@@ -160,6 +160,10 @@ public:
 
   virtual lldb::LanguageType GetLanguageType() const = 0;
 
+  // Implement this function to return the user-defined entry point name
+  // for the language.
+  virtual llvm::StringRef GetUserEntryPointName() const { return {}; }
+
   virtual bool IsTopLevelFunction(Function &function);
 
   virtual bool IsSourceFile(llvm::StringRef file_path) const = 0;

lldb/include/lldb/Target/Target.h

@@ -654,6 +654,8 @@ public:
 
   lldb::BreakpointSP GetBreakpointByID(lldb::break_id_t break_id);
 
+  lldb::BreakpointSP CreateBreakpointAtUserEntry(Status &error);
+
   // Use this to create a file and line breakpoint to a given module or all
   // module it is nullptr
   lldb::BreakpointSP CreateBreakpoint(const FileSpecList *containingModules,

lldb/source/Commands/CommandOptionsProcessLaunch.cpp

@@ -34,11 +34,15 @@ Status CommandOptionsProcessLaunch::SetOptionValue(
   Status error;
   const int short_option = g_process_launch_options[option_idx].short_option;
 
+  TargetSP target_sp =
+      execution_context ? execution_context->GetTargetSP() : TargetSP();
   switch (short_option) {
   case 's': // Stop at program entry point
     launch_info.GetFlags().Set(eLaunchFlagStopAtEntry);
     break;
-
+  case 'm': // Stop at user entry point
+    target_sp->CreateBreakpointAtUserEntry(error);
+    break;
   case 'i': // STDIN for read only
   {
     FileAction action;
@@ -89,8 +93,6 @@ Status CommandOptionsProcessLaunch::SetOptionValue(
     break;
 
   case 'a': {
-    TargetSP target_sp =
-        execution_context ? execution_context->GetTargetSP() : TargetSP();
     PlatformSP platform_sp =
         target_sp ? target_sp->GetPlatform() : PlatformSP();
     launch_info.GetArchitecture() =

lldb/source/Commands/Options.td

@@ -675,6 +675,10 @@ let Command = "platform shell" in {
 let Command = "process launch" in {
   def process_launch_stop_at_entry : Option<"stop-at-entry", "s">,
     Desc<"Stop at the entry point of the program when launching a process.">;
+  def process_launch_stop_at_user_entry : Option<"stop-at-user-entry", "m">,
+    Desc<"Stop at the user entry point when launching a process. For C based "
+    "languages this will be the 'main' function, but this might differ for "
+    "other languages.">;
   def process_launch_disable_aslr : Option<"disable-aslr", "A">, Arg<"Boolean">,
     Desc<"Set whether to disable address space layout randomization when launching a process.">;
   def process_launch_plugin : Option<"plugin", "P">, Arg<"Plugin">,

lldb/source/Plugins/Language/CPlusPlus/CPlusPlusLanguage.h

@@ -103,6 +103,8 @@ public:
     return lldb::eLanguageTypeC_plus_plus;
   }
 
+  llvm::StringRef GetUserEntryPointName() const override { return "main"; }
+
   std::unique_ptr<TypeScavenger> GetTypeScavenger() override;
   lldb::TypeCategoryImplSP GetFormatters() override;
 

lldb/source/Plugins/Language/ObjC/ObjCLanguage.h

@@ -127,6 +127,8 @@ public:
     return lldb::eLanguageTypeObjC;
   }
 
+  llvm::StringRef GetUserEntryPointName() const override { return "main"; }
+
   // Get all possible names for a method. Examples:
   // If method_name is "+[NSString(my_additions) myStringWithCString:]"
   //   variant_names[0] => "+[NSString myStringWithCString:]"

lldb/source/Plugins/Language/ObjCPlusPlus/ObjCPlusPlusLanguage.h

@@ -27,6 +27,8 @@ public:
     return lldb::eLanguageTypeObjC_plus_plus;
   }
 
+  llvm::StringRef GetUserEntryPointName() const override { return "main"; }
+
   llvm::StringRef GetNilReferenceSummaryString() override { return "nil"; }
 
   bool IsSourceFile(llvm::StringRef file_path) const override;

lldb/source/Target/Target.cpp

@@ -335,6 +335,45 @@ BreakpointSP Target::GetBreakpointByID(break_id_t break_id) {
   return bp_sp;
 }
 
+lldb::BreakpointSP
+lldb_private::Target::CreateBreakpointAtUserEntry(Status &error) {
+  ModuleSP main_module_sp = GetExecutableModule();
+  FileSpecList shared_lib_filter;
+  shared_lib_filter.Append(main_module_sp->GetFileSpec());
+  llvm::SetVector<std::string, std::vector<std::string>,
+                  std::unordered_set<std::string>>
+      entryPointNamesSet;
+  for (LanguageType lang_type : Language::GetSupportedLanguages()) {
+    Language *lang = Language::FindPlugin(lang_type);
+    if (!lang) {
+      error.SetErrorString("Language not found\n");
+      return lldb::BreakpointSP();
+    }
+    std::string entryPointName = lang->GetUserEntryPointName().str();
+    if (!entryPointName.empty())
+      entryPointNamesSet.insert(entryPointName);
+  }
+  if (entryPointNamesSet.empty()) {
+    error.SetErrorString("No entry point name found\n");
+    return lldb::BreakpointSP();
+  }
+  BreakpointSP bp_sp = CreateBreakpoint(
+      &shared_lib_filter,
+      /*containingSourceFiles=*/nullptr, entryPointNamesSet.takeVector(),
+      /*func_name_type_mask=*/eFunctionNameTypeFull,
+      /*language=*/eLanguageTypeUnknown,
+      /*offset=*/0,
+      /*skip_prologue=*/eLazyBoolNo,
+      /*internal=*/false,
+      /*hardware=*/false);
+  if (!bp_sp) {
+    error.SetErrorString("Breakpoint creation failed.\n");
+    return lldb::BreakpointSP();
+  }
+  bp_sp->SetOneShot(true);
+  return bp_sp;
+}
+
 BreakpointSP Target::CreateSourceRegexBreakpoint(
     const FileSpecList *containingModules,
     const FileSpecList *source_file_spec_list,

lldb/test/Shell/Commands/command-process-launch-user-entry.test

@@ -0,0 +1,8 @@
+# RUN: %clang_host -g %S/Inputs/main.c -o %t
+# RUN: %lldb %t -s %s -o exit | FileCheck %s
+
+process launch -m
+# CHECK-LABEL: process launch -m
+# CHECK: Process {{.*}} stopped
+# CHECK: stop reason = one-shot breakpoint 1
+# CHECK:   frame #0: {{.*}}`main at main.c