Re[8]: [Gc] Allocating Executable Memory

Ivan Maidanski ivmai at mail.ru
Tue Jul 27 14:33:21 PDT 2010


Hello.

Committed it.

Mon, 26 Jul 2010 09:10:51 -0400 Noah Lavine <noah.b.lavine at gmail.com>:

> Hello,
> 
> It passes all of the tests on my machine. (Although this is only the
> regular GC tests - I don't have any that work specifically for
> executable pages.)
> 
> Noah
> 
> 2010/7/24 Ivan Maidanski <ivmai at mail.ru>:
> > Hello!
> >
> > I've changed the patch a bit.
> >
> > Noah -
> >
> > Could you test it?
> >
> > Hans -
> >
> > We unconditionally allocate executable pages on Win32. In the patch, I've changed this to behave the same way as for Unix. Do you think it's worth doing?
> >
> >
> > Sat, 24 Jul 2010 02:16:29 -0400 Noah Lavine <noah.b.lavine at gmail.com>:
> >
> >> Ooops! Here it is.
> >>
> >> 2010/7/24 Ivan Maidanski <ivmai at mail.ru>:
> >> > Hello.
> >> >
> >> > You forget to attach the patch.
> >> >
> >> > Fri, 23 Jul 2010 20:32:47 -0400 Noah Lavine <noah.b.lavine at gmail.com>:
> >> >
> >> >> Hello,
> >> >>
> >> >> Here is a second version of the patch. I believe it fixes almost
> >> >> everything you said. However, I have a question about changing the
> >> >> behavior on non-unix platforms: the code suggests that these platforms
> >> >> currently don't obey the NO_EXECUTE_PERMISSION configure option, and
> >> >> just always return executable memory. I can change that, but it seems
> >> >> like a separate issue from this change - would you like it as a
> >> >> separate patch?
> >> >>
> >> >> A ChangeLog entry could look like this:
> >> >>
> >> >> 2010-07-23 Noah Lavine <noah.b.lavine at gmail.com>
> >> >> ? ? ? ? * configure.ac: change documentation for NO_EXECUTE_PERMISSION
> >> >> to match following change.
> >> >> ? ? ? ? * os_dep.c: add functions GC_set_executable_pages(int),
> >> >> GC_get_executable_pages() to set and check whether the GC allocator
> >> >> functions will return executable memory. Make the
> >> >> NO_EXECUTE_PERMISSION configuration option determine the default
> >> >> choice.
> >> >> ? ? ? ? * gc.h: add prototypes and documentation comments for
> >> >> GC_set_executable_pages(int) and GC_get_executable_pages().
> >> >>
> >> >> There's also a larger issue which I wanted to ask about because I
> >> >> don't understand the internals of libgc very well: my original idea
> >> >> was that the executable option would take effect immediately after
> >> >> being changed. However, I realized that for instance
> >> >> GC_set_pages_executable(1) could be called at a time when the GC has
> >> >> partially-allocated non-executable pages that it is giving out. Would
> >> >> it be better to try to change the protection on those pages, save them
> >> >> and allocate new executable pages, or just change the documentation on
> >> >> this option so it can only be called just after the library is
> >> >> initialized?
> >> >>
> >> >> Thanks
> >> >> Noah
> >> >>
> >> >> 2010/7/23 Ivan Maidanski <ivmai at mail.ru>:
> >> >> >
> >> >> > The patch is incomplete. gc.h should be affected too. Also supply better doc comments (in gc.h). Update NO_EXECUTE_PERMISSION documentation. Send me Changelog entries please. Also, PROT_EXEC is not defined for every platform (e.g. Win32 which supports executable code in the allocated memory) - we shouldn't define a static variable which is always a const. GC_get_pages_executable() should better actually return 1/0 instead of exec_flag.
> >> >> >
> >> >> > Fri, 23 Jul 2010 15:21:34 -0400 Noah Lavine <noah.b.lavine at gmail.com>:
> >> >> >
> >> >> >> Thanks a lot!
> >> >> >>
> >> >> >> Here is a patch against the latest CVS which implements this. On my
> >> >> >> computer libgc passes all tests with it applied.
> >> >> >>
> >> >> >> Noah
> >> >> >>
> >> >> >> On Fri, Jul 23, 2010 at 3:10 PM, Boehm, Hans <hans.boehm at hp.com> wrote:
> >> >> >> > I don't mind this either. ?We've generally been moving static configuration options to runtime wherever the performance impact was minor. ?We didn't get around to this one yet.
> >> >> >> >
> >> >> >> > Hans
> >> >> >> >
> >> >> >> >> -----Original Message-----
> >> >> >> >> From: gc-bounces at linux.hpl.hp.com [mailto:gc-bounces at linux.hpl.hp.com]
> >> >> >> >> On Behalf Of Ivan Maidanski
> >> >> >> >> Sent: Friday, July 23, 2010 11:40 AM
> >> >> >> >> To: Noah Lavine
> >> >> >> >> Cc: gc at linux.hpl.hp.com
> >> >> >> >> Subject: Re: [Gc] Allocating Executable Memory
> >> >> >> >>
> >> >> >> >> Hello!
> >> >> >> >>
> >> >> >> >> I like the idea.
> >> >> >> >> I don't mind adding this feature in this release (probably Hans
> >> >> >> >> wouldn't neither since the added coded is small and easily verifiable).
> >> >> >> >>
> >> >> >> >> The API should be:
> >> >> >> >> - GC_set_pages_executable(int) // non-zero means executable
> >> >> >> >> - GC_get_pages_executable() // returns non-zero if it is allowed to
> >> >> >> >> execute code in allocated memory
> >> >> >> >>
> >> >> >> >> NO_EXECUTE_PERMISSION controls the initial value only.
> >> >> >> >>
> >> >> >> >> If you'd like to add it, I expect you'll provide the patch against the
> >> >> >> >> current CVS.
> >> >> >> >>
> >> >> >> >>
> >> >> >> >> Fri, 23 Jul 2010 13:28:17 -0400 Noah Lavine <noah.b.lavine at gmail.com>:
> >> >> >> >>
> >> >> >> >> > Hello GC Developers,
> >> >> >> >> >
> >> >> >> >> > I am writing with a feature request for the next version of your
> >> >> >> >> library.
> >> >> >> >> >
> >> >> >> >> > I am working on adding JIT compilation support to GNU Guile (a Scheme
> >> >> >> >> > implementation), which uses this library for garbage collection. In
> >> >> >> >> > order to make GC work, we'll need to allocate executable memory.
> >> >> >> >> > However, I have discovered that allocating executable memory is a
> >> >> >> >> > build-time configuration option (in version 7.1, it appears to be set
> >> >> >> >> > in configure.ac, at lines 401 and 495). This gives Guile something of
> >> >> >> >> > a problem - currently we use whatever libgc is on a user's computer.
> >> >> >> >> > However, the only way to ensure that libgc will allocate executable
> >> >> >> >> > memory would be to build our own version of it, which would add space
> >> >> >> >> > to our executable and be redundant. We could also hack together our
> >> >> >> >> > own memory allocator only for executable memory, but we like using
> >> >> >> >> > your library. :-)
> >> >> >> >> >
> >> >> >> >> > Therefore, I'd like to request that the next version of the library
> >> >> >> >> > have allocating executable memory as a runtime configuration option
> >> >> >> >> > that can be set by programs. I don't think it would affect
> >> >> >> >> performance
> >> >> >> >> > very much - in fact, I can find only two uses of it in the entire
> >> >> >> >> > program (calls to mmap and mprotect in os_dep.c).
> >> >> >> >> >
> >> >> >> >> > I also have a question - is there some way to make an older version
> >> >> >> >> of
> >> >> >> >> > libgc manage executable memory anyway? For instance, if I mmap some
> >> >> >> >> > pages of executable memory, will libgc scan those for pointers even
> >> >> >> >> > though it didn't allocate them? Are there other ways to work around
> >> >> >> >> > this?
> >> >> >> >>
> >> >> >> >> See GC_add_roots.
> >> >> >> >>
> >> >> >> >> >
> >> >> >> >> > Thank you very much
> >> >> >> >> > Noah Lavine
> >> >> >> >> > _______________________________________________
> >> >> >> >> > Gc mailing list
> >> >> >> >> > Gc at linux.hpl.hp.com
> >> >> >> >> > http://www.hpl.hp.com/hosted/linux/mail-archives/gc/
> >> >> >> >>
> >> >> >> >> _______________________________________________
> >> >> >> >> Gc mailing list
> >> >> >> >> Gc at linux.hpl.hp.com
> >> >> >> >> http://www.hpl.hp.com/hosted/linux/mail-archives/gc/
> >> >> >> >
> >> >> >>
> >> >> >>
> >> >> >> ATTACHMENT: application/x-patch add_executable_option.patch_______________________________________________
> >> >> >> Gc mailing list
> >> >> >> Gc at linux.hpl.hp.com
> >> >> >> http://www.hpl.hp.com/hosted/linux/mail-archives/gc/
> >> >> >
> >> >> >
> >> >>
> >> >> _______________________________________________
> >> >> Gc mailing list
> >> >> Gc at linux.hpl.hp.com
> >> >> http://www.hpl.hp.com/hosted/linux/mail-archives/gc/
> >> >
> >>
> >>
> >> ATTACHMENT: application/x-patch add_executable_option.patch_______________________________________________
> >> Gc mailing list
> >> Gc at linux.hpl.hp.com
> >> http://www.hpl.hp.com/hosted/linux/mail-archives/gc/
> >
> >
> 
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