[Gc] Occasionally crash with GraphicsMagick, ImageMagick.

Shi Jie Gung ksc91u_fr at yahoo.fr
Thu May 6 02:17:32 PDT 2010

--- On Thu, 5/6/10, Boehm, Hans <hans.boehm at hp.com>  wrote:

> From: Boehm, Hans <hans.boehm at hp.com>
> Subject: RE: [Gc] Occasionally crash with GraphicsMagick, ImageMagick.
> To: "Shi Jie Gung" <ksc91u_fr at yahoo.fr>, "gc at napali.hpl.hp.com" <gc at napali.hpl.hp.com>
> Date: Thursday, May 6, 2010, 3:32 AM
> My guess is that you are deallocating
> an object that was allocated using the system malloc or some
> other means.  You can confirm by invoking GC_base on
> the objects that's about to be deallocated.  If it
> returns 0, it doesn't belong to the collector.
> The object may be allocated in some other library, where
> you are not intercepting calls.  Or you might be
> allocating using other libc calls, like strdup() or
> memalign(), that you are not currently intercepting.
> Hans

You meant that there are some objects allocated by system's malloc and freed by gc_free?
But I could not find anywhere in graphicsmagick's source code that calls malloc, every memory allocation calls the function I set by MagickAllocFunctions.

Here is another stack tracce from debug version of graphicsmagick and debug version of gc.

Reason: KERN_INVALID_ADDRESS at address: 0x0000000000000008
0x00000001002fb0c3 in GC_remove_from_fl (hhdr=0x1009f0930, n=-1) at allchblk.c:316
316             nhdr -> hb_prev = hhdr -> hb_prev;
(gdb) bt
#0  0x00000001002fb0c3 in GC_remove_from_fl (hhdr=0x1009f0930, n=-1) at allchblk.c:316
#1  0x00000001002fbf07 in GC_freehblk (hbp=0x100cbf000) at allchblk.c:859
#2  0x000000010030cd21 in GC_reclaim_block (hbp=0x100cbf000, report_if_found=0) at reclaim.c:311
#3  0x0000000100303657 in GC_apply_to_all_blocks (fn=0x10030cb25 <GC_reclaim_block>, client_data=0) at headers.c:319
#4  0x000000010030d1c3 in GC_start_reclaim (report_if_found=0) at reclaim.c:518
#5  0x00000001002fd033 in GC_finish_collection () at alloc.c:885
#6  0x00000001002fc6eb in GC_try_to_collect_inner (stop_func=0x1002fbfea <GC_never_stop_func>) at alloc.c:467
#7  0x00000001002fd381 in GC_try_to_collect_general (stop_func=0, force_unmap=0) at alloc.c:967
#8  0x00000001002fd417 in GC_gcollect () at alloc.c:993
#9  0x0000000100000eb0 in main (argc=2, argv=0x7fff5fbff240) at main.cpp:103
Current language:  auto; currently c
(gdb) print nhdr
$1 = (hdr *) 0x0
(gdb) print hhdr
$2 = (hdr *) 0x1009f0930

So why kernel complain can not access 0x08 but print nhdr says 0x0?

(gdb) print nhdr->hb_prev
Cannot access memory at address 0x8
(gdb) print nhdr
$3 = (hdr *) 0x0


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