ldso: remove deprecated support for legacy 'main'

Besides the removal of the legacy 'main' support, this patch simplifies
the lib/startup/_main.cc.

Issue #2199

repos/base/lib/symbols/ld

@@ -400,9 +400,6 @@ _ZnwjPN6Genode9AllocatorE T
 _ZnwjRN6Genode9AllocatorE T
 _ZnwmPN6Genode9AllocatorE T
 _ZnwmRN6Genode9AllocatorE T
-genode_argc D 4
-genode_argv D 8
-genode_envp B 8
 lx_environ B 8
 memcpy W
 memmove W

repos/base/src/ld/genode_dyn.dl

@@ -15,5 +15,4 @@
 	_dtors_end;
 	_ZN9Component9constructERN6Genode3EnvE;
 	_ZN9Component10stack_sizeEv;
-	main;
 };

repos/base/src/ld/genode_dyn.ld

@@ -34,16 +34,15 @@ SECTIONS
 
     /*
      * The ELF entry point is unused for dynamically linked components. The
-     * dynamic linker determined the entry point by looking up the symbol of
-     * the 'Component::construct' function or - if it does not exist - the
-     * 'main' function (for legacy components).
+     * dynamic linker determines the entry point by looking up the symbol of
+     * the 'Component::construct' function.
      *
      * \deprecated  The support for legacy main functions will be removed.
      *
      * The 'KEEP' directive prevents text that is reachable from one of the
      * possible entry points from being garbage collected.
      */
-    KEEP(*(.text._ZN9Component9constructERN6Genode3EnvE .text.main))
+    KEEP(*(.text._ZN9Component9constructERN6Genode3EnvE))
 
     *(.text
       .stub .text.* .gnu.linkonce.t.*)

repos/base/src/lib/ldso/main.cc

@@ -337,18 +337,6 @@ Linker::Ld &Linker::Ld::linker()
 }
 
 
-/*
- * Defined in the startup library, passed to legacy main functions.
- */
-extern char **genode_argv;
-extern int    genode_argc;
-extern char **genode_envp;
-
-static int exit_status;
-
-static void exit_on_suspended() { genode_exit(exit_status); }
-
-
 /**
  * The dynamic binary to load
  */
@@ -452,29 +440,6 @@ struct Linker::Binary : private Root_object, public Elf_object
 			return;
 		}
 
-		/*
-		 * The 'Component::construct' function is missing. This may be the
-		 * case for legacy components that still implement a 'main' function.
-		 *
-		 * \deprecated  the handling of legacy 'main' functions will be removed
-		 */
-		if (Elf::Addr addr = lookup_symbol("main")) {
-			warning("using legacy main function, please convert to 'Component::construct'");
-
-			/* execute static constructors before calling legacy 'main' */
-			finish_static_construction();
-
-			exit_status = ((int (*)(int, char **, char **))addr)(genode_argc,
-			                                                     genode_argv,
-			                                                     genode_envp);
-
-			/* trigger suspend in the entry point */
-			env.ep().schedule_suspend(exit_on_suspended, nullptr);
-
-			/* return to entrypoint and exit via exit_on_suspended() */
-			return;
-		}
-
 		error("dynamic linker: component-entrypoint lookup failed");
 		throw Fatal();
 	}

repos/base/src/lib/startup/_main.cc

@@ -14,9 +14,7 @@
  */
 
 /* Genode includes */
-#include <base/sleep.h>
 #include <base/thread.h>
-#include <base/component.h>
 
 /* platform-specific local helper functions */
 #include <base/internal/globals.h>
@@ -29,8 +27,6 @@ addr_t init_main_thread_result;
 
 static Platform *platform_ptr;
 
-enum { MAIN_THREAD_STACK_SIZE = 16*1024 };
-
 
 /**
  * Satisfy crt0.s in static programs, LDSO overrides this symbol
@@ -42,38 +38,15 @@ void init_rtld()
 	init_cxx_guard();
 }
 
+void * __dso_handle = 0;
+
 
 /**
  * Lower bound of the stack, solely used for sanity checking
  */
 extern unsigned char __initial_stack_base[];
 
 
-/**
- * The first thread in a program
- */
-struct Main_thread : Thread
-{
-	Main_thread()
-	:
-		Thread(Weight::DEFAULT_WEIGHT, "main", MAIN_THREAD_STACK_SIZE, Type::MAIN)
-	{ }
-
-	/**********************
-	 ** Thread interface **
-	 **********************/
-
-	void entry() override { }
-};
-
-
-Main_thread * main_thread()
-{
-	static Main_thread s { };
-	return &s;
-}
-
-
 /**
  * Create a thread object for the main thread
  *
@@ -90,14 +63,28 @@ extern "C" void init_main_thread()
 
 	platform_ptr = &init_platform();
 
-	/* create a thread object for the main thread */
-	main_thread();
+	/*
+	 * Create a 'Thread' object for the main thread
+	 */
+	static constexpr size_t STACK_SIZE = 16*1024;
+
+	struct Main_thread : Thread
+	{
+		Main_thread()
+		:
+			Thread(Weight::DEFAULT_WEIGHT, "main", STACK_SIZE, Type::MAIN)
+		{ }
+
+		void entry() override { /* never executed */ }
+	};
+
+	static Main_thread main_thread { };
 
-	/**
+	/*
 	 * The new stack pointer enables the caller to switch from its current
 	 * environment to the those that the thread object provides.
 	 */
-	addr_t const sp = reinterpret_cast<addr_t>(main_thread()->stack_top());
+	addr_t const sp = reinterpret_cast<addr_t>(main_thread.stack_top());
 	init_main_thread_result = sp;
 
 	/*
@@ -117,26 +104,6 @@ extern "C" void init_main_thread()
 	}
 }
 
-void * __dso_handle = 0;
-
-
-/**
- * Dummy default arguments for main function
- */
-static char  argv0[] = { '_', 'm', 'a', 'i', 'n', 0};
-static char *argv[1] = { argv0 };
-
-
-/**
- * Arguments for main function
- *
- * These global variables may be initialized by a constructor provided by an
- * external library.
- */
-char **genode_argv = argv;
-int    genode_argc = 1;
-char **genode_envp = 0;
-
 
 namespace Genode {
 
@@ -157,22 +124,10 @@ namespace Genode {
 }
 
 
-extern "C" int _main()
+extern "C" int _main() /* executed with the stack within the stack area */
 {
-	Genode::bootstrap_component(*platform_ptr);
+	bootstrap_component(*platform_ptr);
 
 	/* never reached */
 	return 0;
 }
-
-
-extern int main(int argc, char **argv, char **envp);
-
-
-void Component::construct(Genode::Env &env) __attribute__((weak));
-void Component::construct(Genode::Env &)
-{
-	/* call real main function */
-	main(genode_argc, genode_argv, genode_envp);
-}
-