Re[4]: [Gc] boehm port to Native Client

Ivan Maidanski ivmai at mail.ru
Sat Apr 16 01:48:45 PDT 2011


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> wrote:
Hi Elijah,

Any progress or comments?

Sat, 15 Jan 2011 15:36:47 +0300 Ivan Maidanski <ivmai at mail.ru>:

> Hello Elijah,
>
> Fri, 14 Jan 2011 15:36:34 -0800 письмо от Elijah Taylor <
> elijahtaylor at google.com (sentmsg?compose&To=elijahtaylor at 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
> (sentmsg?compose&To=ivmai at 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
> (sentmsg?compose&To=elijahtaylor at 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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