Re[6]: [Gc] boehm port to Native Client

Ivan Maidanski ivmai at mail.ru
Mon Mar 5 07:01:59 PST 2012


Hi Elijah,

I've cherry-picked your latest commit regarding NaCl from mono/libgc to BDWGC master branch (with minor modifications):
https://github.com/ivmai/bdwgc/commit/14f2760d584c18fc8a1f305f5ed0a6d13ff5918a

I wonder where is nacl_register_gc_hooks defined?

Thanks.

18 04 2011, 22:31 Elijah Taylor <elijahtaylor at google.com>:
> Hi Ivan,
> 
> If I can add a couple of functions to our pthread implementation
> (pthread_getattr_np and pthread_getattr_getstack) then we should be able to
> just use the GC_LINUX_THREADS version and take off the "!defined(NACL)".
>  I'll let you know of my progress when I have something to report.
> 
> -Elijah
> 
> On Sat, Apr 16, 2011 at 1:48 AM, Ivan Maidanski <ivmai at mail.ru> wrote:
> 
> > Hi Elijah,
> >
> > Could you also provide GC_get_stack_base() implementation for NaCl? (just
> > for the completeness of the port)
> >
> > Thanks.
> >
> > Sat, 22 Jan 2011 16:23:32 -0800 Elijah Taylor <elijahtaylor at google.com>:
> >
> > Hi Ivan,
> >
> > Sorry I haven't gotten back to you yet, I've been busy with other things
> > this last week.  I'm planning on addressing the feedback you've given me so
> > far in the next week, and I can send you a more detailed response to your
> > other questions at that time.  Thanks for the help so far.
> >
> > -Elijah
> >
> >
> > On Sat, Jan 22, 2011 at 9:09 AM, Ivan Maidanski <ivmai at mail.ru<http://sentmsg?compose&To=ivmai@mail.ru>
> > > wrote:
> >
> >> Hi Elijah,
> >>
> >> Any progress or comments?
> >>
> >> Sat, 15 Jan 2011 15:36:47 +0300 Ivan Maidanski <ivmai at mail.ru<http://sentmsg?compose&To=ivmai@mail.ru>
> >> >:
> >>
> >> > Hello Elijah,
> >> >
> >> > Fri, 14 Jan 2011 15:36:34 -0800 письмо от Elijah Taylor <
> >> > elijahtaylor at google.com<http://sentmsg?compose&To=elijahtaylor@google.com>(sentmsg?compose&To=
> >> elijahtaylor at google.com<http://sentmsg?compose&To=elijahtaylor@google.com>)
> >> >:
> >> >
> >> > > Hi Ivan,
> >> > >
> >> > > Thanks for taking a look, I'm pleasantly surprised by the level of
> >> detail
> >> > > here.  Specific replies inline:
> >> > >
> >> > >
> >> > > On Fri, Jan 14, 2011 at 2:50 PM, Ivan Maidanski < ivmai at mail.ru<http://sentmsg?compose&To=ivmai@mail.ru>
> >> > (sentmsg?compose&To=ivmai at mail.ru<http://sentmsg?compose&To=ivmai@mail.ru>)
> >> > wrote:
> >> > >
> >> > > - the patch in  naclports repository contains a typo in a macro
> >> definition
> >> > > > (MAC_TYPE -> MACH_TYPE);
> >> > >
> >> > > Oops, will fix.
> >> >
> >> > Why not to leave MACH_TYPE as-is (e.g. "I386", etc.)? NaCl is a kind of
> >> OS not
> >> > a kind of machine hardware.
> >> > Is eg. I386 defined for x86?
> >> >
> >> > Also, please add a mapping comment in gcconfig.h (around "Feel free to
> >> add
> >> > more clauses here").
> >> >
> >> > >
> >> > > > - the patch in  naclports repository looks more suitable for gc v72
> >> than
> >> > > > that for mono/libgc;
> >> > > >
> >> > >
> >> > > This patch is meant to be applied to vanilla gc6.8.  The mono/libgc
> >> port is
> >> > > already patched directly into mono's code repository.
> >> >
> >> > Yes, I only meant the vanilla gc6.8 patch contains some more code (eg,
> >> for
> >> > PARALLEL_MARK) not present in mono/libgc.
> >> >
> >> > > > - gc_pthread_redirects.h (which is a public one) should not test
> >> NACL
> >> > macro
> >> > > > (or, at least, while less desirable, it should be prefixed with
> >> GC_);
> >> > > >
> >> > >
> >> > > Ok, makes sense, I think I didn't realize this was a public header.
> >>  Though
> >> > > that explains why I had to add a test for __native_client__  (which is
> >> > > defined in our toolchain).  I'll fix this.
> >> > >
> >> > > > - it's not clear why you need to explicitly undef STACK_GRAN,
> >> > USE_M[UN]MAP,
> >> > > > etc. in gcconfig.h;
> >> > > >
> >> > >
> >> > > I'll do some investigation, but IIRC these were needed at one point
> >> for me.
> >> > > There's a good chance these may be unnecessary and vestigial.
> >> >
> >> > There should none "undef" (no other target undefining them).
> >> >
> >> > If mmap is supported by NaCl then it might be possible to support
> >> > USE_M[UN]MAP.
> >> >
> >> > > > - is MPROTECT_VDB supported or not?;
> >> > >
> >> > > Is MPROTECT_VDB equivalent to catching protection violations in the GC
> >> code?
> >> > > If so, then no, we don't support anything like that right now.
> >>  Protection
> >> > > violation in NaCl == instant death.
> >> >
> >> > Ok, so MPROTECT_VDB (i.e., incremental/generation collection) is not
> >> > supported.
> >> >
> >> > > > - if you you want to port gc72 please use the recent CVS snapshot
> >> (it
> >> > would
> >> > > > be easier to me to review and commit it);
> >> > >
> >> > > I've been grabbing source from
> >> > >  http://www.hpl.hp.com/personal/Hans_Boehm/gc/gc_source/
> >> > (http://www.hpl.hp.com/personal/Hans_Boehm/gc/gc_source/)  ... can you
> >> point
> >> > me
> >> > > to where I should be getting the latest?  It's not immediately obvious
> >> to
> >> > > me.
> >> >
> >> > http://bdwgc.cvs.sourceforge.net/viewvc/bdwgc/bdwgc/
> >> > (For convenience, I have a recent snapshot as a tarball which I use for
> >> my
> >> > project -
> >> > http://www.ivmaisoft.com/_mirror/hpl/bdwgc-7_2alpha5-20110107.tar.bz2)
> >> >
> >> > > - not sure that HEURISTIC1 really works reliably there (in short,
> >> HEURISTIC1
> >> > > > means you treat stack pointer at GC_init call as stack bottom - is
> >> it
> >> > > > guaranteed that GC_init call is always done at higher stack
> >> addresses than
> >> > > > any other GC call);
> >> > > >
> >> > >
> >> > > HEURISTIC2 will definitely not work for us as it wants to use a
> >> segfault to
> >> > > detect running over the stack.  I've set STACK_GRAN to 64K, so as long
> >> as
> >> > > the stack doesn't grow beyond that size before GC_init, we should be
> >> ok,as
> >> > > right?  The stack for the main thread right now in NaCl lives at a
> >> fixed
> >> > > address usually, but that isn't guaranteed for all future time, so I'd
> >> > > prefer not to hard code magic numbers here.
> >> >
> >> > No, HEURISTIC2 won't work without signals, but there are other
> >> alternatives:
> >> > - if threads-support is on then is it possible to use
> >> > USE_GET_STACKBASE_FOR_MAIN?;
> >> > - is it possible to LINUX_STACKBOTTOM (if we are on real Linux)?
> >> > - for NaCl on Cygwin, it might be possible to use
> >> GC_get_[main_]stack_base
> >> > based on __asm__ ("%fs:4").
> >> >
> >> > > > - is the GC port compilable (and working) on other (non-Linux)
> >> platforms
> >> > > > (eg., Cygwin);
> >> > > >
> >> > >
> >> > > Native Client is meant to be portable, so it should run on any x86 or
> >> x86-64
> >> > > machine once it's built.  In terms of building, I haven't built this
> >> gc port
> >> > > personally on Mac or Windows, but I just checked our build bot logs
> >> and they
> >> > > seem to be building ok on Mac and in Cygwin.
> >> >
> >> > So, eg. DARWIN, GC_DARWIN_THREADS,  WIN32, CYGWIN, GC_WIN32_THREADS
> >> won't ever
> >> > be defined when building NaCl, right?
> >> > Is GC_LINUX_THREADS defined when building NaCl with multi-threaded
> >> support?
> >> >
> >> > I have very little knowledge of NaCl - could you briefly explain what
> >> does
> >> > stand for NaCl portability - is it possible to call Win32 API if I'm
> >> compiling
> >> > on Cygwin or should I use the NaCl API (and, thus, the compiled binary
> >> code
> >> > will run on any x86 target)?
> >> >
> >> > If NaCl is some kind of OS then LINUX, DARWIN, WIN32, etc shouldn't be
> >> defined
> >> > (even if __linux__ defined) if NACL.
> >> > Same for GC_xxx_THREADS - I think GC_NACL_THREADS could be defined
> >> instead of
> >> > GC_LINUX_THREADS, etc.
> >> >
> >> > I also think that I386 and X86_64 should stay defined for respectively
> >> the
> >> > corresponding CPU type (I guess it is already for NaCl but i haven't
> >> checked
> >> > yet)
> >> > I think there should be 2 ifdef NACL define OS_TYPE "NACL" ... sections
> >> (one
> >> > for every supported CPU).
> >> >
> >> > > > - for non-static GC-internal symbols use GC_ prefix (eg. for
> >> > > > nacl_thread_parked);
> >> > > > - define SIG_SUSPEND to -1 (instead of 0) as it is returned by
> >> > > > GC_get_suspend_signal;
> >> > > > - GC functions called from NaCl it self (eg, nacl_pre_syscall_hook)
> >> shoud
> >> > > > be tagged with some attribute (like public GC functions are) both
> >> for code
> >> > > > readability and to prevent that symbols stripping when compiled as a
> >> > shared
> >> > > > lib with -DGC_DLL);
> >> > > >
> >> > >
> >> > > I'll address these issues.  (note that NaCl currently doesn't support
> >> shared
> >> > > libs yet so your dll example won't happen, but I agree that these
> >> should be
> >> > > treated like other public GC functions)
> >> >
> >> > Ok. But what is eg. nacl_pre_syscall_hook() - a callback from the NaCl
> >> > subsystem? (I guess this should be treated as GC public API)
> >> >
> >> > Of course, use STATIC or static where possible (all STATIC symbols start
> >> with
> >> > GC_, while static typically not).
> >> > More tips: use GC_INNER and GC_EXTERN for internal global variables; use
> >> > GC_INNER for internal functions.
> >> >
> >> > > > - libatomic_ops does not use signals API (except for CAS emulation
> >> which
> >> > is
> >> > > > not used for x86/x64).
> >> > >
> >> > > I think I saw sigprocmask and related functions and assumed the worst,
> >> but I
> >> > > see now that's windows code.  Looking at the x86 variants it looks
> >> like a
> >> > > NaCl port of libatomic_ops is probably not going to be too bad.  I'll
> >> look
> >> > > into this eventually.
> >> >
> >> > Most probably, it work w/o any porting afforts but it would be good to
> >> port
> >> > atomic_ops.c (similar to what I did for Win32-pthreads targets - see
> >> > AO_USE_WIN32_PTHREADS, I guess you should add AO_USE_NACL macro testing
> >> in
> >> > that file (looks easy to add). I think it's worth doing first (and
> >> submit me a
> >> > separate patch for libatomics_op when done).
> >> >
> >> > What's about GC_HAVE_BUILTIN_BACKTRACE and GC_CAN_SAVE_CALL_STACKS? At
> >> least,
> >> > gc.h should be consistent with the GC implementation (I mean eg. if
> >> > GC_HAVE_BUILTIN_BACKTRACE not supported then it shouldn't be defined in
> >> gc.h
> >> > regardless of __linux__, _MSC_VER, etc. provided  __native_client__).
> >> Same for
> >> > GC_ADD_CALLER, GC_RETURN_ADDR.
> >> >
> >> > Regards.
> >> >
> >> > > > PS. Let me not do the benefits analysis (probably someone else can
> >> do
> >> > > > this).
> >> > > >
> >> > > Well, if the gc7.2 port is as easy as it's looking now, I think it's
> >> > > probably worth doing it.  I would still love to hear anyone chime in
> >> on the
> >> > > benefits of gc7.2 vs 6.8 though
> >> > >
> >> > > > Regards.
> >> > > >
> >> > > > Thu, 13 Jan 2011 10:21:03 -0800 Elijah Taylor <
> >> elijahtaylor at google.com<http://sentmsg?compose&To=elijahtaylor@google.com>
> >> > (sentmsg?compose&To=elijahtaylor at google.com<http://sentmsg?compose&To=elijahtaylor@google.com>)
> >> >:
> >> > > >
> >> > > > > Hi GC folks,
> >> > > >
> >> > > > > I saw a little chatter in the archives related to porting libgc to
> >> > Native
> >> > > > Client, so I joined this list to share some details. I'm the
> >> engineer at
> >> > > > Google who ported of libgc to Native Client for Mono. I've also
> >> included a
> >> > > > patch for vanilla gc6.8 in our naclports repository:
> >> > > >  http://code.google.com/p/naclports/ (
> >> http://code.google.com/p/naclports/)
> >> > . This version will be available to
> >> > > > users that want to use libgc as part of their Native Client
> >> projects.
> >> > > >
> >> > > > > Before porting gc6.8 I had attempted to port one of the newer
> >> versions,
> >> > > > gc7.2alpha4, but ran into snags. The largest snag right now I think
> >> is
> >> > that
> >> > > > gc 7+ includes libatomic_ops which will require some non-trivial
> >> effort in
> >> > > > order to work under Native Client. Most notably we don't support
> >> signals;
> >> > > > that was the biggest effort in porting libgc in the first place for
> >> NaCl,
> >> > > > and I assume that will require the most work in porting
> >> libatomic_ops too.
> >> > > >
> >> > > > > Can someone give me the high level details of what kind of things
> >> we
> >> > > > might be missing if we only support gc6.8 instead of the latest
> >> version?
> >> > > > Because of our thread stopping implementation, we may not even
> >> benefit
> >> > from
> >> > > > some of the newer features. I just wanted to get a sense of what the
> >> > > > benefits are of getting a newer version available for users.
> >> > > >
> >> > > > > -Elijah
> >>
> >>
> >
> >
> 
> 



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