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

Paolo Carlesi pcarlesi at gmail.com
Mon Dec 14 04:55:35 EST 2015


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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