Re: pkg/39012 (boehm-gc coredumps on GC_INIT under hpcmips (mipsel))

[ben%wongs.net@localhost]

As I suspected, a quick work around is to simply disable
DYNAMIC_LOADING in the Boehm garbage collector. I have recompiled
gc-7.0 and verified that libgc works as expected (or, at least, it
doesn't dump core like the one currently available in pkgsrc).

I have a patch (below) which skips the #define of DYNAMIC_LOADING when
NETBSD and MIPSEL are defined. While this is not the optimal solution,
it is more correct then what is currently shipping. By the way, this
patch to boehm-gc will make the w3m package, and perhaps others,
compile cleanly instead of breaking.

        --Ben

--- include/private/gcconfig.h.orig     2007-06-28 17:00:09.000000000 -0700
+++ include/private/gcconfig.h  2008-07-20 05:25:28.000000000 -0700
@@ -1397,7 +1397,13 @@
         extern int etext[];
 #       define DATASTART GC_data_start
 #       define NEED_FIND_LIMIT
-#       define DYNAMIC_LOADING
+/* Sadly, DYNAMIC_LOADING is broken for NetBSD/mipsel as of July 2008 */
+#      ifdef __MIPSEL__
+#        warning "DYNAMIC_LOADING support is broken for little endian MIPS"
+#        undef DYNAMIC_LOADING
+#      else
+#         define DYNAMIC_LOADING
+#      endif /* __MIPSEL__ */
 #     else
 #       define DATASTART ((ptr_t) 0x10000000)
 #       define STACKBOTTOM ((ptr_t) 0x7ffff000)


On 7/7/08, ben%wongs.net@localhost <ben%wongs.net@localhost> wrote:
> Additional information:
>
> I have tried building boehm-gc from the latest pkgsrc and can now
> provide a more precise backtrace.
>
>   Script started on Mon Jul  7 05:30:12 2008
>   bash-3.2# gdb ./a.out
>   GNU gdb 5.3nb1
>   Copyright 2002 Free Software Foundation, Inc.
>   This GDB was configured as "mipsel--netbsd"...
>   (gdb) run
>   Starting program: /usr/pkgsrc/devel/boehm-gc/work/gc-7.0/a.out
>
>   Program received signal SIGSEGV, Segmentation fault.
>   0x7df456e8 in GC_find_limit_with_bound () at os_dep.c:917
>   917                 GC_noop1((word)(*result));
>   (gdb) c
>   Continuing.
>
>   Program received signal SIGSEGV, Segmentation fault.
>   0x7df456e8 in GC_find_limit_with_bound () at os_dep.c:917
>   917                 GC_noop1((word)(*result));
>   (gdb) c
>   Continuing.
>
>   Program received signal SIGSEGV, Segmentation fault.
>   0x7df3b920 in GC_FirstDLOpenedLinkMap () at dyn_load.c:455
>   455                         = ((struct r_debug *)(dp->d_un.d_ptr))->r_map;
>
>   (gdb) list
>   450     if( cachedResult == 0 ) {
>   451         int tag;
>   452         for( dp = _DYNAMIC; (tag = dp->d_tag) != 0; dp++ ) {
>   453             if( tag == DT_DEBUG ) {
>   454                 struct link_map *lm
>   455                         = ((struct r_debug *)(dp->d_un.d_ptr))->r_map;
>   456                 if( lm != 0 ) cachedResult = lm->l_next; /*
> might be NIL */
>   457                 break;
>   458             }
>   459         }
>
>   (gdb) bt
>   #0  0x7df3b920 in GC_FirstDLOpenedLinkMap () at dyn_load.c:455
>   #1  0x7df3b9f0 in GC_register_dynamic_libraries () at dyn_load.c:475
>   #2  0x7df42cd0 in GC_push_roots () from ./.libs/libgc.so.1
>   #3  0x7df422d4 in GC_mark_some () from ./.libs/libgc.so.1
>   #4  0x7df3809c in GC_stopped_mark () from ./.libs/libgc.so.1
>   #5  0x7df384d8 in GC_try_to_collect_inner () from ./.libs/libgc.so.1
>   #6  0x00400adc in main (argc=1, argv=0x7fffdca4, envp=0x7fffdcac) at
> gctest.c:7
>   (gdb) quit
>   The program is running.  Exit anyway? (y or n) y
>   bash-3.2# exit
>
>   Script done on Mon Jul  7 05:31:04 2008
>
> Note that the first two segfaults are red herrings. Apparently some
> OSes (including NetBSD?) do not have a native way to find the
> beginning and end of the main data segment, so boehm-gc must perform a
> search at startup which causes segmentation faults.
>
> The true bug appears to be releated to the dynamic library tracing
> routines in dyn_load.c. The following page has helpful information
> about the porting changes necessary to enable dynamic library support:
>
>   http://www.hpl.hp.com/personal/Hans_Boehm/gc/porting.html
>
> The page also mentions that if DYNAMIC_LOADING is undefined in
> gcconfig.h, tracing of dynamic library data will be disabled. This
> might be a quick, if rather unsatisfying, way to get boehm-gc
> "working" in NetBSD/mipsel.
>
> --Ben
>