ldso: interface to get infos about loaded objects

This patch enhances the 'base/shared_object.h' interface of the dynamic
linker with the function 'for_each_loaded_object', which allows the
caller to obtain information about the currently loaded binary and
shared libraries.

The new interface is a base mechanism needed for implementing 'fork' in
the libc.

Issue #3478

repos/base/include/base/shared_object.h

@@ -18,11 +18,13 @@
 #include <base/allocator.h>
 #include <base/exception.h>
 #include <base/stdint.h>
+#include <rom_session/rom_session.h>
 
 namespace Genode {
 
 	class  Shared_object;
 	struct Address_info;
+	struct Dynamic_linker;
 };
 
 
@@ -118,4 +120,55 @@ struct Genode::Address_info
 	Address_info(Genode::addr_t addr);
 };
 
+
+class Genode::Dynamic_linker
+{
+	public:
+
+		struct Object_info
+		{
+			/* name of shared library, or "binary" for the main program */
+			typedef String<64> Name;
+			Name name;
+
+			Rom_dataspace_capability ds_cap;
+
+			/* pointer to the start of the read/writeable segment */
+			void *rw_start;
+
+			/* size of the read-writeable segment in bytes */
+			size_t rw_size;
+		};
+
+	private:
+
+		struct For_each_fn : Interface
+		{
+			virtual void supply_object_info(Object_info const &) const = 0;
+		};
+
+		static void _for_each_loaded_object(Env &, For_each_fn const &);
+
+	public:
+
+		/**
+		 * Call 'fn' for each loaded object with 'Object_info' as argument
+		 */
+		template <typename FN>
+		static inline void for_each_loaded_object(Env &env, FN const &fn)
+		{
+			struct For_each_fn_impl : For_each_fn
+			{
+				FN const &fn;
+
+				void supply_object_info(Object_info const &info) const { fn(info); }
+
+				For_each_fn_impl(FN const &fn) : fn(fn) { }
+
+			} wrapped_fn { fn };
+
+			_for_each_loaded_object(env, wrapped_fn);
+		}
+};
+
 #endif /* _INCLUDE__BASE__SHARED_OBJECT_H_ */

repos/base/lib/symbols/ld

@@ -106,6 +106,7 @@ _ZN6Genode13Shared_objectD1Ev T
 _ZN6Genode13Shared_objectD2Ev T
 _ZN6Genode13sleep_foreverEv T
 _ZN6Genode14Capability_map6insertEmm T
+_ZN6Genode14Dynamic_linker23_for_each_loaded_objectERNS_3EnvERKNS0_11For_each_fnE T
 _ZN6Genode14Rpc_entrypoint13_free_rpc_capERNS_10Pd_sessionENS_17Native_capabilityE T
 _ZN6Genode14Rpc_entrypoint14_alloc_rpc_capERNS_10Pd_sessionENS_17Native_capabilityEm T
 _ZN6Genode14Rpc_entrypoint17_activation_entryEv T

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

@@ -28,6 +28,12 @@ namespace Linker {
 	struct Phdr;
 	struct File;
 	struct Elf_file;
+
+	static inline bool is_rx(Elf::Phdr const &ph) {
+		return ((ph.p_flags & PF_MASK) == (PF_R | PF_X)); }
+
+	static inline bool is_rw(Elf::Phdr const &ph) {
+		return ((ph.p_flags & PF_MASK) == (PF_R | PF_W)); }
 }
 
 
@@ -67,6 +73,17 @@ struct Linker::File
 	}
 
 	unsigned elf_phdr_count() const { return phdr.count; }
+
+	template <typename FN>
+	void with_rw_phdr(FN const &fn) const
+	{
+		for (unsigned i = 0; i < phdr.count; i++) {
+			if (is_rw(phdr.phdr[i])) {
+				fn(phdr.phdr[i]);
+				return;
+			}
+		}
+	}
 };
 
 
@@ -212,12 +229,6 @@ struct Linker::Elf_file : File
 		}
 	}
 
-	bool is_rx(Elf::Phdr const &ph) {
-		return ((ph.p_flags & PF_MASK) == (PF_R | PF_X)); }
-
-	bool is_rw(Elf::Phdr const &ph) {
-		return ((ph.p_flags & PF_MASK) == (PF_R | PF_W)); }
-
 	/**
 	 * Load PT_LOAD segments
 	 */

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

@@ -659,6 +659,29 @@ void Genode::exec_static_constructors()
 }
 
 
+void Genode::Dynamic_linker::_for_each_loaded_object(Env &, For_each_fn const &fn)
+{
+	Elf_object::obj_list()->for_each([&] (Object const &obj) {
+
+		Elf_file const *elf_file_ptr =
+			obj.file() ? dynamic_cast<Elf_file const *>(obj.file()) : nullptr;
+
+		if (!elf_file_ptr)
+			return;
+
+		elf_file_ptr->with_rw_phdr([&] (Elf::Phdr const &phdr) {
+
+			Object_info info { .name     = obj.name(),
+			                   .ds_cap   = elf_file_ptr->rom_cap,
+			                   .rw_start = (void *)(obj.reloc_base() + phdr.p_vaddr),
+			                   .rw_size  = phdr.p_memsz };
+
+			fn.supply_object_info(info);
+		});
+	});
+}
+
+
 void Component::construct(Genode::Env &env)
 {
 	/* read configuration */