Re: [Gc] Allocating Executable Memory
ivmai at mail.ru
Fri Jul 23 13:10:42 PDT 2010
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.
> 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
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