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

Adam adam.mlmb at gmail.com
Mon Dec 14 05:39:59 EST 2015


I'm interested in understanding what caused that sigsegv too.

2015-12-14 17:55 GMT+08:00 Paolo Carlesi <pcarlesi at gmail.com>:

> 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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