[RFC PATCH 4/6] powerpc/vxworks: [hack] add crti.o file

[Rasmus Villemoes <rasmus dot villemoes at prevas dot dk>]

The run-time linker on VxWorks almost supports the "modern"
.init_array/.fini_array way of dealing with static constructors and
destructors. On load of a module, it simply looks for a symbol _ctors
and expects that to be a NULL-terminated array of function pointers to
call (and similarly for _dtors on unload), and it does indeed call
_ctors in forward order and _dtors in reverse order. So all we need to
do is ensure the symbols _ctors and _dtors exist and arrange for a zero
terminator.

At first, I tried simply doing this in the linker script, i.e. something
like

PROVIDE(_ctors = .);
KEEP (*(SORT_BY_INIT_PRIORITY(.init_array.*)))
KEEP (*(.init_array))
LONG(0)

similar to the default linker scripts that just provide
__init_array_{start,end} symbols. Unfortunately, that is not quite
enough, since the _ctors symbol ends up with NOTYPE rather than OBJECT,
so it does not get recognized as a _ctors array by the VxWorks
runtime. I couldn't find a way to define the type of a linker-provided
symbol, so I'm resorting to this "hack".

I thought of also defining the symbol in the assembly file, but
then we'd have to put it in the .init_array.00000 section to also make
the _ctors array span static constructors with an init_priority. And
a corresponding crtn.o with a 0 entry would have to go in the
.init_array itself. I don't like that asymmetry between the crt{i,o}
files, and I think it's cleaner that the linker script defines both ends
of the array - this crti.o is merely a hack around my inability to
define the type of _ctors in the linker language.

2018-06-04  Rasmus Villemoes  <rasmus.villemoes@prevas.dk>

libgcc/

	* config.host: Add vxworks-crti.o to extra_parts for
          powerpc-wrs-vxworks.
	* config/rs6000/t-vxworks: New file.
	* config/rs6000/vxworks-crti.S: New file.
---
 libgcc/config.host                  |  4 ++--
 libgcc/config/rs6000/t-vxworks      |  5 +++++
 libgcc/config/rs6000/vxworks-crti.S | 10 ++++++++++
 3 files changed, 17 insertions(+), 2 deletions(-)
 create mode 100644 libgcc/config/rs6000/t-vxworks
 create mode 100644 libgcc/config/rs6000/vxworks-crti.S

diff --git a/libgcc/config.host b/libgcc/config.host
index b75c86bd4a6..a0da84647a6 100644
--- a/libgcc/config.host
+++ b/libgcc/config.host
@@ -1111,8 +1111,8 @@ powerpc*-*-linux*)
 	md_unwind_header=rs6000/linux-unwind.h
 	;;
 powerpc-wrs-vxworks*)
-	tmake_file="$tmake_file rs6000/t-ppccomm rs6000/t-savresfgpr t-fdpbit"
-	extra_parts="$extra_parts crtbegin.o crtend.o"
+	tmake_file="$tmake_file rs6000/t-ppccomm rs6000/t-savresfgpr rs6000/t-vxworks t-fdpbit"
+	extra_parts="$extra_parts crtbegin.o crtend.o vxworks-crti.o"
 	;;
 powerpc-*-lynxos*)
 	tmake_file="$tmake_file rs6000/t-lynx t-fdpbit"
diff --git a/libgcc/config/rs6000/t-vxworks b/libgcc/config/rs6000/t-vxworks
new file mode 100644
index 00000000000..ab9bee121c9
--- /dev/null
+++ b/libgcc/config/rs6000/t-vxworks
@@ -0,0 +1,5 @@
+# We build crti.o, which serves to set the type of _ctors and _dtors
+# symbols to "object".
+
+vxworks-crti$(objext): $(srcdir)/config/rs6000/vxworks-crti.S
+	$(crt_compile) -c $<
diff --git a/libgcc/config/rs6000/vxworks-crti.S b/libgcc/config/rs6000/vxworks-crti.S
new file mode 100644
index 00000000000..14d571f8fa2
--- /dev/null
+++ b/libgcc/config/rs6000/vxworks-crti.S
@@ -0,0 +1,10 @@
+/* This file just ensures the global (linker-supplied) symbols _ctors
+   and _dtors get the appropriate type.  */
+
+	.ident	"GNU C vxworks-crti.o"
+
+	.globl _ctors
+	.type	_ctors, @object
+
+	.globl _dtors
+	.type	_dtors, @object
-- 
2.15.1