Bert,
On Mon, Nov 26, 2012 at 5:16 AM, Bert Freudenberg bert@freudenbergs.dewrote:
On 2012-11-25, at 17:03, "David T. Lewis" lewis@mail.msen.com wrote:
To summarize my understanding of this issue (see below for background):
- powerpcspe is variant of powerpc that lacks certain parts of the
powerpc
instruction set, as explained here:
http://wiki.debian.org/PowerPCSPEPort
- The FFI plugin has architecture-specific assembler modules that set
up the entry points for FFI calls. The assembly module for powerpc is platforms/unix/plugins/SqueakFFIPrims/ppc-sysv-asm.S
- The ppc-sysv-asm.S module uses one or more instructions ('lfd',
possibly
others) that are not available on the powerpcspe processor, and the the module cannot be compiled on powerpcspe.
- The solution for the Debian build is to not build the FFI plugin when
compiling for powerpcspe. This is done by passing the
--without-SqueakFFIPrims
option to the cmake configure when building on powerpcspe.
- The configuration is done in a file called debian/rules, and the
provided
squeak-vm.patch is a patch for that rules file. This file is not part of the Squeak VM platforms sources and is presumably maintained externally by the Debian folks.
- The right way to fix the build problem in the platforms sources would
be
to modify platforms/unix/plugins/SqueakFFIPrims/config.cmake to disable the FFI plugin for powerpcspe at configure time. This is probably easy to do, although I do not have a way to try it myself.
- Extra credit: If someone wanted FFI to work on powerpcspe, the way to
make
this happen would be to write a variation of ppc-sysv-asm.S for
powerpcspe
and add it to config.cmake.
Dave
Instead of disabling FFI it might be possible to fall back to libffi, as is done for some other architectures (e.g. ARM).
IMO, much better would be to add PPC support to ThreadedFFIPlugin. This is a framework for cross-platform FFI, currently instantiated for x86, but it has all the hooks one needs to write a PPC interface. This uses minimal assembler, essentially only the occasional asm statement, e.g. to set the flag that indicates a call has active floating-point parameters, or to adjust the stack pointer after an alloca. Being written in terms of the C library's alloca stack allocator to create the outgoing argument frame it is a) more efficient since arguments are not copied from a marshalling space to the outgoing stack frame as occurs in the old FFI, and b) reentrant, since there is no static area used for marshalling.
I've written support for PPC for VisualWorks in the same way so I do know this approach does work and would be happy to help anyone with a PPC mahcine who was interested in biting the bullet. The tricky issues are the need to pass register arguments alongside the stacked arguments, and the need to avoid overwriting the marshalling area of the alloca'ed argument frame when calling functions involved in marshalling arguments. The first issue is solved by always calling the external function as if it had 8 register arguments, and passing 8 arguments, hence loading the argument registers. The second issue is solved by over allocating and cutting back the stack with an asm statement just before the call.
You'll find that the framework was written with this in mind even if the support for PPC and ARM (and SPARC and AXP and MIPS, all of which I wrote for the VisualWorks VM) isn't complete yet.
cheers Eliot
- Bert -
On Mon, Nov 19, 2012 at 06:38:10PM +0100, Bert Freudenberg wrote:
Begin forwarded message:
Resent-From: Roland Stigge stigge@antcom.de From: Roland Stigge stigge@antcom.de Subject: Bug#693633: squeak-vm: FTBFS on powerpcspe (asm stfd/lfd) Date: 18. November 2012 21:10:04 MEZ Resent-To: debian-bugs-dist@lists.debian.org To: Debian Bug Tracking System submit@bugs.debian.org Resent-Cc: Debian Squeak Team <
pkg-squeak-devel@lists.alioth.debian.org>
Reply-To: Roland Stigge stigge@antcom.de, 693633@bugs.debian.org
Package: squeak-vm Version: 1:4.4.7.2357-1.1 Severity: wishlist Tags: sid patch User: debian-powerpcspe@breakpoint.cc Usertags: powerpcspe
Hi,
squeak-vm FTBFS on powerpcspe [1] like this:
[ 82%] Building ASM object
SqueakFFIPrims/CMakeFiles/SqueakFFIPrims.dir/<C2><AB>PKGBUILDDIR<C2><BB>/unix/plugins/SqueakFFIPrims/ppc-sysv-asm.S.o
/PKGBUILDDIR/unix/plugins/SqueakFFIPrims/ppc-sysv-asm.S: Assembler
messages:
/PKGBUILDDIR/unix/plugins/SqueakFFIPrims/ppc-sysv-asm.S:109: Error:
Unrecognized opcode: `lfd'
[...]
There are some asm statements that only work on powerpc but not on
powerpcspe.
Attaching a patch that fixes it by disabling the SqueakFFIPrims plugin
on
powerpcspe.
Thanks,
Roland
[1] http://wiki.debian.org/PowerPCSPEPort
-- System Information: Debian Release: wheezy/sid APT prefers unstable APT policy: (500, 'unstable'), (1, 'experimental') Architecture: amd64 (x86_64)
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(ignored: LC_ALL set to en_GB.UTF-8)
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