NetBSD/external
christos 0db9e20bfb From Jake Hamby
For several years I've been eager to find the time to fix the bugs
in C++ exceptions on VAX to get them working on NetBSD, because
theyâve been broken for many years and it looked like only a few
changes were needed to get them working. Without C++ exceptions,
the NetBSD test suite canât be run. The good news is that I was
able to fix all the bugs in the VAX machine description to make
C++ exceptions work in GCC 4.8.5 (version unimportant). I wrote a
blog post explaining the bugs, with patches:


Here's a short summary, with the diffs in text form at the end of this email.

1) Replace #define FRAME_POINTER_CFA_OFFSET(FNDECL) 0 with #define
ARG_POINTER_CFA_OFFSET(FNDECL) 0 in gcc/config/vax/elf.h and
gcc/config/vax/vax.h. This changes the definition of __builtin_dwarf_cfa()
to return %ap instead of %fp, which correctly points to CFA.
Previously, the stack unwinder was crashing in _Unwind_RaiseException()
trying to follow bad pointers from the initial CFA.

2) Define EH_RETURN_DATA_REGNO(N) to include only R2 and R3 (instead
of R2-R5) and add code to vax_expand_prologue() in gcc/config/vax/vax.c
to add R2-R3 to the procedure entry mask but only if crtl->calls_eh_return
is set. This fixes a crash when the stack unwinder tried to write
values to R2 and R3 in the previous stack frame via
__builtin_eh_return_data_regno (0) and __builtin_eh_return_data_regno (1).

3) Removed definitions of EH_RETURN_STACKADJ_RTX and STARTING_FRAME_OFFSET
from gcc/config/vax/elf.h. It's not necessary to remember the stack
adjustment or to waste four bytes on every stack frame for a value
that's not needed. Also remove the suspicious changes in
gcc/config/vax/vax.md to the definitions of call_pop and call_value
regarding DW_CFA_GNU_args_size and EH unwinding. I reverted to the
previous versions from an older version of GCC, adding a few useful
comments that had been removed.

4) The last bug is the one I understand the least. I'm hoping
someone reading this can implement a correct fix. What I was seeing
after making all the previous changes to fix the other bugs is that
my test program failed to catch any exceptions, but instead returned
normally to the original return path.

Investigation revealed that GCC was correctly generating the
necessary move instruction to copy the second parameter passed to
__builtin_eh_return() into the return address, because
EH_RETURN_HANDLER_RTX had been defined correctly in config/vax/elf.h.
Hereâs what the call looks like in gcc/except.c:

#ifdef EH_RETURN_HANDLER_RTX
      rtx insn = emit_move_insn (EH_RETURN_HANDLER_RTX, crtl->eh.ehr_handler);
#else
      error ("__builtin_eh_return not supported on this target");
#endif

The problem was that the optimizer is deleting the final move
instruction when I compile with -O or higher. The assembly code at
-O0 (no optimization) generated for the __builtin_eh_return() call
at the end of _Unwind_RaiseException() looked like:

	calls $2,_Unwind_DebugHook
	movl -12(%fp),%r1
	movl %r1,16(%fp)
	ret
	.cfi_endproc

But then when I compiled with -O1 or -O2, all I saw was:

	calls $2,_Unwind_DebugHook
	ret
	.cfi_endproc

This was a mystery for me and I donât know enough about how the
final peephole optimizer works to really track down why it thinks
it can remove the move call to store the previous return address.
My workaround was to add a call to RTX_FRAME_RELATED_P (insn) = 1;
after the emit_move_insn() in gcc/except.c, which was used in
vax_expand_prologue() to mark the procedure entry mask.

By making this change, the optimizer no longer removes the call to
write the value to the previous stack pointer, but it adds an extra
line of .cfi exception info, which seems unnecessary since the code
is immediately going to return from the call and any adjustment
made by the DWARF stack unwinder will already have been done. Hereâs
what the optimized code looks like with the patch (%r6 had been
loaded earlier):

	calls $2,_Unwind_DebugHook
	movl %r6,16(%fp)
	.cfi_offset 6, -36
	ret
	.cfi_endproc

With that final change, C++ exception handling now finally works
on NetBSD/vax, and I was able to successfully run the vast majority
of the tests in the ATF testsuite, which had been completely
inaccessible when I started due to both atf-run and atf-report
immediately dumping core due to the bad pointers that I fixed. Now
I have a bunch of new bugs to track down fixes for, but I think
this was the hardest set of problems that needed to be solved to
bring NetBSD on VAX up to the level of the other NetBSD ports.

Here are the diffs I have so far. They should apply to any recent
version of GCC (tested on GCC 4.8.5). With the exception of the
hack to gcc/except.c, the other diffs are ready to submit to NetBSD
as well as to upstream GCC. The fix Iâd like to see for the final
problem I discovered of the emit_move_insn() being deleted by the
optimizer would be another patch to one of the files in the
gcc/config/vax directory to explain to the optimizer that writing
to 16(%fp) is important and not something to be deleted from the
epilogue (perhaps it thinks itâs writing to a local variable in
the frame that's about to be destroyed?).

I didn't see any indication that any other GCC ports required
anything special to tell the optimizer not to delete the move
instruction to EH_RETURN_HANDLER_RTX, so the other suspicion I have
is that there may be a bug specific to VAX's peephole optimizer or
related functions. Any ideas?
2016-03-23 12:52:43 +00:00
..
apache2 Add support for parsing IPv6 nameservers found in resolv.conf. 2015-10-15 16:14:40 +00:00
atheros
broadcom/rpi-firmware/dist Update RPI firmware to version after the following commit 2016-03-11 12:34:57 +00:00
bsd Describe -M 2016-03-23 10:14:07 +00:00
cddl write references as pointers XXX: 2016-03-18 17:11:04 +00:00
gpl2 Hardcode man page dates to date of groff release (September 4, 2005 2016-03-16 23:52:04 +00:00
gpl3 From Jake Hamby 2016-03-23 12:52:43 +00:00
historical PR/50199 - fix for strftime called with empty string. 2015-11-03 14:15:08 +00:00
ibm-public
intel-fw-eula
intel-fw-public
lgpl3
mit Install ftttdrv.h, which was apparently overlooked at some point 2016-03-21 05:23:39 +00:00
public-domain update for 2016b 2016-03-15 17:33:14 +00:00
realtek
zlib/pigz
Makefile
README

$NetBSD: README,v 1.15 2012/06/14 04:14:36 riz Exp $

Organization of Sources:

This directory hierarchy is using an organization that separates
source for programs that we have obtained from external third
parties (where NetBSD is not the primary maintainer) from the
system source.

The hierarchy is grouped by license, and then package per license,
and is organized as follows:

	external/

	    Makefile
			Descend into the license sub-directories.

	    <license>/
			Per-license sub-directories.

		Makefile
			Descend into the package sub-directories.

		<package>/
			Per-package sub-directories.

		    Makefile
			Build the package.
			
		    dist/
			The third-party source for a given package.

		    bin/
		    lib/
		    sbin/
			BSD makefiles "reach over" from these into
			"../dist/".

This arrangement allows for packages to be easily disabled or
excised as necessary, either on a per-license or per-package basis.

The licenses currently used are:

	apache2		Apache 2.0 license.
			http://www.opensource.org/licenses/apache2.0.php

	atheros		Atheros License.

	bsd		BSD (or equivalent) licensed software, possibly with
			the "advertising clause".
			http://www.opensource.org/licenses/bsd-license.php

	cddl		Common Development and Distribution License (the sun
			license which is based on the Mozilla Public License
			version 1.1).
			http://www.opensource.org/licenses/cddl1.php

	gpl2		GNU Public License, version 2 (or earlier).
			http://www.opensource.org/licenses/gpl-2.0.php

	gpl3		GNU Public License, version 3.
			http://www.opensource.org/licenses/gpl-3.0.html

	historical	Lucent's old license:
			http://www.opensource.org/licenses/historical.php
			
	ibm-public	IBM's public license:
			http://www.opensource.org/licenses/ibmpl.php

	intel-fw-eula	Intel firmware license with redistribution
			restricted to OEM.

	intel-fw-public	Intel firmware license permitting redistribution with
			terms similar to BSD licensed software.

	intel-public	Intel license permitting redistribution with
			terms similar to BSD licensed software.

	mit		MIT (X11) style license.
			http://www.opensource.org/licenses/mit-license.php

	public-domain	Non-license for code that has been explicitly put
			into the Public Domain.

	realtek		RealTek license.

	zlib		Zlib (BSD-like) license.
			http://www.zlib.net/zlib_license.html

If a package has components covered by different licenses
(for example, GPL2 and the LGPL), use the <license> subdirectory
for the more restrictive license.

If a package allows the choice of a license to use, we'll
generally use the less restrictive license.

If in doubt about where a package should be located, please
contact <core@NetBSD.org> for advice.


Migration Strategy:


Eventually src/dist (and associated framework in other base source
directories) and src/gnu will be migrated to this hierarchy.


Maintenance Strategy:

The sources under src/external/<license>/<package>/dist/ are
generally a combination of a published distribution plus changes
that we submit to the maintainers and that are not yet published
by them.

Make sure all changes made to the external sources are submitted
to the appropriate maintainer, but only after coordinating with
the NetBSD maintainers.