Tigthen libc_internal and crtstuff for VxWorks shared objects

This change tightens and documents the use of libc_internal, then
strengthens the VxWorks crtstuff objects for the support of shared
libraries. In particular:

- Define __dso_handle, which libstdc++.so requires,

- Provide _init and _fini functions to run through the init/fini arrays
  for shared libs in configurations which HAVE_INITFINI_ARRAY_SUPPORT.

The init/fini functions are provided by libc_internal.a for static links
but with slightly different names and we don't want to risk dragging other
libc_internal contents in the closure accidentally so make sure we don't
link with it.

As for the !vxworks crtstuff, the new shared libs specific bits are
conditioned by a CRTSTUFFS_O macro, for which we provide new Makefile
fragment.

The bits to actually use the fragment and the shared objects will
be added by a forthcoming change, as part of a more general configury
update for shared libs.

The change also adds guards the eh table registration code
in vxcrtstuff so the objects can be used for either init/fini
or eh tables independently.

2021-12-07  Fred Konrad  <konrad@adacore.com>
	    Olivier Hainque  <hainque@adacore.com>

gcc/
	* config/vxworks.h (VXWORKS_BASE_LIBS_RTP): Guard -lc_internal
	on !shared+!non-static and document.
	(VXWORKS_LIB_SPEC): Remove the bits intended to drag the
	init/fini functions from libc_internal in the shared lib case.
	(VX_CRTBEGIN_SPEC/VX_CRTEND_SPEC): Use vxcrtstuff objects also in
	configurations with shared lib and INITFINI_ARRAY support.

libgcc/
	* config/t-vxcrtstuffS: New Makefile fragment.
	* config/vxcrtstuff.c: Provide __dso_handle. Provide _init/_fini
	functions for INITFINI_ARRAY support in shared libs and guard
	the definition of eh table registration functions on conditions
	indicating they are needed.

2 files changed, 81 insertions, 5 deletions

diff --git a/libgcc/config/t-vxcrtstuffS b/libgcc/config/t-vxcrtstuffS
new file mode 100644
index 00000000000..6b65b0005be
--- /dev/null
+++ b/libgcc/config/t-vxcrtstuffS
@@ -0,0 +1,9 @@
+# Shared versions of vx_crt{begin,end}.o, those one must be compiled only
+# when the shared libraries are available
+
+vx_crtbeginS.o: $(srcdir)/config/vxcrtstuff.c
+	$(crt_compile) $(CRTSTUFF_T_CFLAGS_S) -DCRT_BEGIN -c $< -DCRTSTUFFS_O
+vx_crtendS.o: $(srcdir)/config/vxcrtstuff.c
+	$(crt_compile) $(CRTSTUFF_T_CFLAGS_S) -DCRT_END -c $< -DCRTSTUFFS_O
+
+EXTRA_PARTS += vx_crtbeginS.o vx_crtendS.o
diff --git a/libgcc/config/vxcrtstuff.c b/libgcc/config/vxcrtstuff.c
index c15e15e54e9..80f51f7399d 100644
--- a/libgcc/config/vxcrtstuff.c
+++ b/libgcc/config/vxcrtstuff.c
@@ -50,15 +50,25 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #define USE_CDTORS_SECTIONS
 #endif
 
+#if DWARF2_UNWIND_INFO && !defined(__USING_SJLJ_EXCEPTIONS__)
+#define USE_EH_FRAME_REGISTRY
+#endif
+
 /*  ------------------------------ crtbegin -------------------------------  */
 
 #ifdef CRT_BEGIN
 
-/* Stick a label at the beginning of the frame unwind info so we can register
-   and deregister it with the exception handling library code.  */
-static const char __EH_FRAME_BEGIN__[]
-__attribute__((section(__LIBGCC_EH_FRAME_SECTION_NAME__), aligned(4)))
-  = { };
+#if DEFAULT_USE_CXA_ATEXIT && defined(__RTP__)
+/* This mimics the crtstuff.c behavior.  dso_handle should be NULL for the
+   main program (in vx_crtbegin.o) and a unique value for the shared libraries
+   (in vx_crtbeginS.o).   */
+extern void *__dso_handle __attribute__ ((__visibility__ ("hidden")));
+#ifdef CRTSTUFFS_O
+void *__dso_handle = &__dso_handle;
+#else
+void *__dso_handle = 0;
+#endif
+#endif /* DEFAULT_USE_CXA_ATEXIT */
 
 /* Determine what names to use for the constructor/destructor functions.  */
 
@@ -89,6 +99,53 @@ __attribute__((section(__LIBGCC_EH_FRAME_SECTION_NAME__), aligned(4)))
 #define EH_CTOR_ATTRIBUTE __attribute__((constructor (101)))
 #define EH_DTOR_ATTRIBUTE __attribute__((destructor (101)))
 
+/* Provide the init/fini array support functions for shared libraries,
+   where we don't want to drag libc_internal contents blindly and which
+   provides functions with a slightly different name anyway.  */
+
+#if HAVE_INITFINI_ARRAY_SUPPORT && defined(CRTSTUFFS_O)
+
+/* Run through the .init_array, .fini_array sections.  The linker script
+   *must* provide __init_array_start, __init_array_end, __fini_array_start,
+   __fini_array_end symbols.  */
+
+typedef void (*initfini_ptr) (void);
+extern initfini_ptr __init_array_start[];
+extern initfini_ptr __init_array_end[];
+extern initfini_ptr __fini_array_start[];
+extern initfini_ptr __fini_array_end[];
+
+/* Provide the actual code through static functions, which don't need
+   to be exposed in the shared lib interface.  */
+
+static void __exec_init_array(void)
+{
+  initfini_ptr *fn;
+  for (fn = __init_array_start; fn < __init_array_end; ++fn)
+    (*fn)();
+}
+
+static void __exec_fini_array(void)
+{
+  initfini_ptr *fn;
+  for (fn = __fini_array_end - 1; fn >= __fini_array_start; --fn)
+    (*fn)();
+}
+
+/* Reference the two above functions as the init / fini function.  */
+
+void __attribute__ ((__section__  (".init"))) _init()
+{
+  __exec_init_array();
+}
+
+void __attribute__ ((__section__  (".fini"))) _fini()
+{
+  __exec_fini_array();
+}
+
+#endif /* __CRTSTUFFS_O__ */
+
 #else /* !USE_INITFINI_ARRAY  */
 
 /* Note: Even in case of .ctors/.dtors sections, we can't use the attribute
@@ -100,6 +157,13 @@ __attribute__((section(__LIBGCC_EH_FRAME_SECTION_NAME__), aligned(4)))
 
 #endif /* USE_INITFINI_ARRAY  */
 
+#ifdef USE_EH_FRAME_REGISTRY
+/* Stick a label at the beginning of the frame unwind info so we can register
+   and deregister it with the exception handling library code.  */
+static const char __EH_FRAME_BEGIN__[]
+__attribute__((section(__LIBGCC_EH_FRAME_SECTION_NAME__), aligned(4)))
+  = { };
+
 EH_LINKAGE EH_CTOR_ATTRIBUTE void EH_CTOR_NAME (void)
 {
   static struct object object;
@@ -110,6 +174,7 @@ EH_LINKAGE EH_DTOR_ATTRIBUTE void EH_DTOR_NAME (void)
 {
   __deregister_frame_info (__EH_FRAME_BEGIN__);
 }
+#endif /* USE_EH_FRAME_REGISTRY */
 
 #ifdef USE_CDTORS_SECTIONS
 /* As explained above, we need to manually build the sections here as the
@@ -126,6 +191,7 @@ static void (* volatile eh_registration_dtors[])()
 
 #elif defined (CRT_END) /* ! CRT_BEGIN */
 
+#ifdef USE_EH_FRAME_REGISTRY
 /* Terminate the frame unwind info section with a 4byte 0 as a sentinel;
    this would be the 'length' field in a real FDE.  */
 
@@ -133,6 +199,7 @@ static const char __FRAME_END__[]
      __attribute__ ((used, section(__LIBGCC_EH_FRAME_SECTION_NAME__),
 		     aligned(4)))
   = { 0, 0, 0, 0 };
+#endif /* USE_EH_FRAME_REGISTRY */
 
 #else /* ! CRT_BEGIN & ! CRT_END */