[gambit-list] Segfault on OSX using Gambit's C Interface

Adam adam.mlmb at gmail.com
Tue Dec 15 13:25:27 EST 2015


Paolo, wait, what is your definition of your My type here - "scheme-object"?


2015-12-15 3:46 GMT+08:00 Paolo Carlesi <pcarlesi at gmail.com>:

> Thank you for the workaround!
>
> What is the best way to generate a foreign c-type object ?
>
> This seems to me the best approach (sorry if it's obvious to everybody but
> me):
>
> (define make-My (c-lambda () My "___result_voidstar =
> ___EXT(___alloc_rc)(sizeof(struct My));"))
> (define My->* (c-lambda (My) My*/nonnull "___result_voidstar = &___arg1;"))
>
> has the advantage of not wasting time / space creating a new foreign
> object and a copy, like *->My below does.
> It also doesn't trigger the c-lambda bug, not that I have verified
> carefully yet.
> Members can easily be set up with a syntax like (My-x-set! (My->* xoxo)
> #xdeadbeef) .
> Is this approach correct?
>
> Thanks Again
>
> Paolo
>
> Il giorno 14/dic/2015, alle ore 18:02, Marc Feeley <
> feeley at iro.umontreal.ca> ha scritto:
>
> > There appears to be a bug in the FFI when using a c-lambda with inline
> code that returns a foreign object.  So for now you will have to define a C
> function that does the work and use the name of that function in the
> c-lambda.  In other words:
> >
> > (c-declare #<<c-declare-end
> >
> > My indirect_My_star(My *ptr) { return *ptr; }
> >
> > c-declare-end
> > )
> >
> > (define *->My (c-lambda (My*/nonnull) My "indirect_My_star"))
> >
> > Marc
> >
> >
> >> On Dec 14, 2015, at 4:55 AM, Paolo Carlesi <pcarlesi at gmail.com> wrote:
> >>
> >> Hello,
> >>
> >> I'm experiencing regular segfaults on OSX 10.9.5, with the sample code
> shown below.
> >> Tested with Gambit 4.8.1 + GCC 4.9  and with packaged Gambit 4.7.3 +
> LLVM.
> >> No issue at all on Linux, GCC 4.8, with both Gambit 4.2.8 and Gambit
> 4.8.2.
> >> Of course I may be doing something silly.
> >>
> >> A simple struct, "My" is generated inside a c procedure, then passed
> multiple times to another c-lambda procedure (*->My).
> >> It's a simplified model of the code produced by a FFI SDL2 Library I'm
> using.
> >> The doc says that the foreign object (xoxo in the example) should not
> be released while the scheme code is still referencing it.
> >> I am seeing the refcount going wildly in the negative, one for each
> call to *->My
> >> The only way -- clumsy -- I have found to avoid this is to increment
> the reference count with ___addref_rc ( not shown here ).
> >>
> >> What's wrong here?
> >> Thanks!
> >>
> >>
> >> LLDB output:
> >>
> >> Process 48149 launched: '/Users/paolo/scheme/spazz/fromlin' (x86_64)
> >> Process 48149 stopped
> >> * thread #1: tid = 0x40e3c9, 0x000000010000770c fromlin`___release_rc +
> 28, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS
> (code=EXC_I386_GPFLT)
> >>   frame #0: 0x000000010000770c fromlin`___release_rc + 28
> >> fromlin`___release_rc + 28:
> >> -> 0x10000770c:  movq   %rax, (%rdx)
> >>  0x10000770f:  movq   %rdx, 0x8(%rax)
> >>  0x100007713:  jmp    0x100010240               ; ___free_mem
> >>  0x100007718:  nopl   (%rax,%rax)
> >>
> >> stack trace:
> >>
> >> (lldb) bt
> >> * thread #1: tid = 0x40e3c9, 0x000000010000770c fromlin`___release_rc +
> 28, queue = 'com.apple.main-thread', stop reason = EXC_BAD_ACCESS
> (code=EXC_I386_GPFLT)
> >> * frame #0: 0x000000010000770c fromlin`___release_rc + 28
> >>   frame #1: 0x0000000100002579 fromlin`___release_fn0 + 9
> >>   frame #2: 0x0000000100009009 fromlin`___garbage_collect + 3497
> >>   frame #3: 0x00000001000091bf fromlin`___alloc_scmobj + 255
> >>   frame #4: 0x000000010000d4eb fromlin`___POINTER_to_SCMOBJ + 43
> >>   frame #5: 0x000000010000d5e4 fromlin`___STRUCT_to_SCMOBJ + 20
> >>   frame #6: 0x0000000100002112 fromlin`___H__20_fromlin + 3378
> >>   frame #7: 0x0000000100004aa4 fromlin`___call + 372
> >>   frame #8: 0x0000000100004bc6 fromlin`___setup_pstate + 262
> >>   frame #9: 0x00000001000063be fromlin`___setup + 3950
> >> (lldb)
> >>
> >>
> >> ;; SAMPLE CODE
> >>
> >> (c-declare #<<c-declare-end
> >>
> >> typedef struct My {
> >> int r;
> >> } My;
> >>
> >> c-declare-end
> >> )
> >>
> >> (begin
> >> (c-define-type My (struct "My"))
> >> (c-define-type My* (pointer My (My*)))
> >> (c-define-type My*/nonnull (nonnull-pointer My (My*)))
> >> (c-define-type My*/release-rc (nonnull-pointer My (My*)
> "___release_My")))
> >>
> >>
> >> (begin
> >>   (c-declare #<<c-declare-end
> >> static ___SCMOBJ ___release_My( void* ptr ) {
> >>   ___EXT(___release_rc)( ptr );
> >>   return ___FIX(___NO_ERR);
> >> }
> >> c-declare-end
> >>   )
> >>
> >>   (define alloc-My (c-lambda () My*/release-rc "___result_voidstar =
> ___EXT(___alloc_rc)( sizeof( struct My ));"))
> >>   (define *->My (c-lambda (My*/nonnull) My "___result_voidstar =
> (My*)___arg1;"))
> >>   (define My-r (c-lambda (My*/nonnull) unsigned-int8 "___result =
> ___arg1->r;"))
> >>   (define My-r-set! (c-lambda (My*/nonnull unsigned-int8) void
> "___arg1->r = ___arg2;")))
> >>
> >> (define (evil)
> >>  (let ((xoxo (alloc-My)))
> >>     (My-r-set! xoxo #xff)
> >>     (let loop ((c 1))
> >>         (begin
> >>             (if (= 0 (remainder c 10000))
> >>                 (begin (display c) (newline)))
> >>             (*->My xoxo)
> >>             (loop (+ 1 c))))))
> >>
> >> (evil)
> >>
> >> ;;END CODE
> >>
> >>
> >>
> >>
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>
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