ldso: check ctors sections of shared-object deps

The sole existence of shared-object dependencies lead to fatal
static-constructor errors before. Now, ldso checks if the ctors section
of objects in the init list are non-empty before whining.

Issue #2759

repos/base/src/lib/ldso/include/init.h

@@ -104,6 +104,15 @@ struct Linker::Init : List<Object>
 			exec_static_constructors();
 	}
 
+	bool needs_static_construction()
+	{
+		for (Object *obj = first(); obj; obj = obj->next_init())
+			if (obj->needs_static_construction())
+				return true;
+
+		return false;
+	}
+
 	void exec_static_constructors()
 	{
 		in_progress = true;

repos/base/src/lib/ldso/include/linker.h

@@ -132,6 +132,8 @@ class Linker::Object : private Fifo<Object>::Element,
 
 		Object *_next_object() const { return List<Object>::Element::next(); }
 
+		Elf::Addr _symbol_address(char const *name);
+
 		Name        _name       { };
 		File const *_file       { nullptr };
 		Elf::Addr   _reloc_base { 0 };
@@ -195,6 +197,8 @@ class Linker::Object : private Fifo<Object>::Element,
 		 * Return address info for symboal at addr
 		 */
 		virtual Symbol_info symbol_at_address(addr_t addr) const = 0;
+
+		bool needs_static_construction();
 };
 
 

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

@@ -385,10 +385,7 @@ struct Linker::Binary : private Root_object, public Elf_object
 	{
 		if (static_construction_finished) return false;
 
-		Func * const ctors_start = (Func *)lookup_symbol("_ctors_start");
+		return Init::list()->needs_static_construction();
-		Func * const ctors_end   = (Func *)lookup_symbol("_ctors_end");
-
-		return (ctors_end != ctors_start) || Init::list()->contains_deps();
 	}
 
 	void finish_static_construction()
@@ -477,6 +474,28 @@ struct Linker::Binary : private Root_object, public Elf_object
 };
 
 
+/**********************************
+ ** Linker object implementation **
+ **********************************/
+
+Elf::Addr Linker::Object::_symbol_address(char const *name)
+{
+	unsigned long   hash = Hash_table::hash(name);
+	Elf::Sym const *sym  = dynamic().lookup_symbol(name, hash);
+
+	if (sym)
+		return reloc_base() + sym->st_value;
+	else
+		return Elf::Addr(0);
+}
+
+
+bool Linker::Object::needs_static_construction()
+{
+	return _symbol_address("_ctors_end") != _symbol_address("_ctors_start");
+}
+
+
 /***************************************
  ** Global Linker namespace functions **
  ***************************************/

repos/libports/src/test/fatfs_blkio/component.cc

@@ -6,8 +6,6 @@ extern int main (int argc, char* argv[]);
 
 void Libc::Component::construct(Libc::Env &env)
 {
-	env.exec_static_constructors();
-
 	Genode::Heap heap(env.ram(), env.rm());
 	Fatfs::block_init(env, heap);