Cleanup shared-object support mechanics

The former ldso-startup static library (now called ldso_so_support) is
used to spice each shared object/library with local support code for the
dynamic linker (execution of static constructors and ARM-EABI).
Therefore, the library must be statically linked to each dynamic
library.

As a result recipes for dynamic libraries must always depend on the "so"
API, which makes ldso_so_support.mk and so_support.c available
independent of "base". Additionally, ldso_so_support is also provided in
the libc API to cut the dependency early for libc/posix libraries.

Issue genodelabs#3720

repos/base/lib/mk/ldso_so_support.mk

@@ -0,0 +1,3 @@
+SRC_C = so_support.c
+
+vpath so_support.c $(call select_from_repositories,src/lib/ldso)

repos/base/mk/dep_lib.mk

@@ -81,7 +81,7 @@ include $(BASE_DIR)/mk/base-libs.mk
 include $(LIB_MK)
 
 ifdef SHARED_LIB
-LIBS += ldso-startup
+LIBS += ldso_so_support
 endif
 
 #

repos/base/mk/lib.mk

@@ -181,10 +181,11 @@ $(LIB_A): $(OBJECTS)
 	$(VERBOSE)$(AR) -rcs $@ $(OBJECTS)
 
 #
-# Link ldso-startup library to each shared library
+# Link ldso-support library to each shared library to provide local hook
+# functions for constructors and ARM
 #
 ifdef SHARED_LIB
-override ARCHIVES += ldso-startup.lib.a
+override ARCHIVES += ldso_so_support.lib.a
 endif
 
 #
@@ -208,10 +209,6 @@ STATIC_LIBS_BRIEF := $(subst $(LIB_CACHE_DIR),$$libs,$(STATIC_LIBS))
 # (LIB_SO_DEPS) to the library to store the library-dependency information in
 # the generated shared object.
 #
-# The 'ldso-startup/startup.o' object file, which contains the support code for
-# constructing static objects must be specified as object file to prevent the
-# linker from garbage-collecting it.
-#
 
 #
 # Default entry point of shared libraries

repos/base/recipes/api/base/content.mk

@@ -7,7 +7,7 @@ include:
 	mkdir -p include
 	cp -r $(REP_DIR)/include/* $@/
 
-LIB_MK_FILES := base.mk ld.mk ldso-startup.mk
+LIB_MK_FILES := base.mk ld.mk ldso_so_support.mk
 
 lib:
 	mkdir -p lib/mk lib/symbols
@@ -21,6 +21,11 @@ mk/spec:
 	mkdir -p $@
 	cp $(foreach spec,$(SPECS),$(REP_DIR)/mk/spec/$(spec).mk) $@
 
+content: lib/mk/ldso_so_support.mk src/lib/ldso/so_support.c
+
+lib/mk/ldso_so_support.mk src/lib/ldso/so_support.c:
+	$(mirror_from_rep_dir)
+
 LICENSE:
 	cp $(GENODE_DIR)/LICENSE $@
 

repos/base/recipes/api/so/content.mk

@@ -1,6 +1,6 @@
-content: lib/mk/ldso-startup.mk LICENSE
+content: lib/mk/ldso_so_support.mk src/lib/ldso/so_support.c LICENSE
 
-lib/mk/ldso-startup.mk:
+lib/mk/ldso_so_support.mk src/lib/ldso/so_support.c:
 	$(mirror_from_rep_dir)
 
 LICENSE:

repos/base/src/lib/ldso/so_support.c

@@ -0,0 +1,71 @@
+/**
+ * \brief  Shared-object support code
+ * \author Sebastian Sumpf
+ * \author Christian Helmuth
+ * \date   2009-08-14
+ *
+ * Support code comprises hooks for execution of static constructors and
+ * ARM-EABI dynamic linking.
+ *
+ * The ARM cross compiler uses the __gnu_Unwind_Find_exidx hook to locate a
+ * 'ARM.exidx' section within a shared object. For this to work
+ * 'dl_unwind_find_exidx' is excuted by 'ldso', which returns the section
+ * address if it finds a shared object within the range of the provieded
+ * program counter.
+ */
+
+/*
+ * Copyright (C) 2009-2020 Genode Labs GmbH
+ *
+ * This file is part of the Genode OS framework, which is distributed
+ * under the terms of the GNU Affero General Public License version 3.
+ */
+
+#define BEG { (ld_hook) ~1U }
+#define END { (ld_hook) 0   }
+#define SECTION(x) __attribute__((used,section( x )))
+
+typedef void (*ld_hook)(void);
+static ld_hook _lctors_start[1] SECTION("_mark_ctors_start") = BEG;
+static ld_hook _lctors_end[1]   SECTION("_mark_ctors_end")   = END;
+
+/*
+ * '__dso_handle' needs to be defined in the main program and in each shared
+ * object. Because ld.lib.so is both of them, '__dso_handle' is weak here.
+ */
+void *__dso_handle __attribute__((__visibility__("hidden")))
+                   __attribute__((weak))                     = &__dso_handle;
+
+/* called by dynamic linker on library startup (ld.lib.so) */
+extern void _init(void) __attribute__((used,section(".init")));
+extern void _init(void)
+{
+	/* call static constructors */
+	for (ld_hook *func = _lctors_end; func > _lctors_start + 1; (*--func)());
+}
+
+
+/*
+ * from gcc/config/arm/unwind-arm.h
+ */
+typedef unsigned _Unwind_Ptr __attribute__((__mode__(__pointer__)));
+
+
+/*
+ * Dummy for static libs, implemented in ldso for dynamic case
+ */
+extern _Unwind_Ptr dl_unwind_find_exidx(_Unwind_Ptr pc, int *pcount) __attribute__((weak));
+extern _Unwind_Ptr dl_unwind_find_exidx(_Unwind_Ptr pc, int *pcount)
+{
+	return 0;
+}
+
+
+/*
+ * Called from libgcc_eh.a file 'gcc/config/arm/unwind-arm.c' in function
+ * 'get_eit_entry'
+ */
+extern _Unwind_Ptr __gnu_Unwind_Find_exidx (_Unwind_Ptr pc, int *pcount)
+{
+	return dl_unwind_find_exidx(pc, pcount);
+}

repos/libports/recipes/api/libc/content.mk

@@ -18,6 +18,12 @@ include:
 	cp -r $(REP_DIR)/include/libc-genode $@/
 	cp    $(REP_DIR)/src/lib/libc/internal/legacy.h $@/libc/
 
+content: lib/mk/ldso_so_support.mk src/lib/ldso/so_support.c
+
+lib/mk/ldso_so_support.mk src/lib/ldso/so_support.c:
+	mkdir -p $(dir $@)
+	cp $(GENODE_DIR)/repos/base/$@ $@
+
 content: LICENSE
 
 LICENSE:

repos/libports/recipes/api/posix/content.mk

@@ -1,14 +1,10 @@
 MIRROR_FROM_REP_DIR := lib/symbols/posix lib/import/import-posix.mk
 
-content: $(MIRROR_FROM_REP_DIR) LICENSE lib/mk/base.mk lib/mk/ldso-startup.mk
+content: $(MIRROR_FROM_REP_DIR) LICENSE
 
 $(MIRROR_FROM_REP_DIR):
 	$(mirror_from_rep_dir)
 
-lib/mk/base.mk lib/mk/ldso-startup.mk:
-	mkdir -p $(dir $@)
-	touch $@
-
 LICENSE:
 	cp $(GENODE_DIR)/LICENSE $@
 

repos/libports/recipes/src/test-ldso/used_apis

@@ -1,2 +1,3 @@
 base
 libc
+so

repos/os/recipes/src/vfs/used_apis

@@ -6,3 +6,4 @@ report_session
 rtc_session
 terminal_session
 vfs
+so