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@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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