GNU Hurd/ open issues/ crash server

Welcome to... ... the GNU Hurd!

Given an a.out executable that only does raise (SIGABRT), invoking that one...

  • ... against crash-dump-core will...

    • ... not overwrite existing core files.

      Is this reasonable? Linux does overwrite them, for example.

    • ... show big variances in running-time behavior:

      $ TIMEFORMAT='real %R user %U system %S'
$ rm -f core; time env CRASHSERVER=/servers/crash-dump-core ./a.out; ls -l core
Aborted (core dumped)
real 1.350 user 0.000 system 0.010
-rw------- 1 tschwinge tschwinge 17031168 Jul  7 21:59 core
$ rm -f core; time env CRASHSERVER=/servers/crash-dump-core ./a.out; ls -l core
Aborted (core dumped)
real 22.771 user 0.000 system 0.010
-rw------- 1 tschwinge tschwinge 17031168 Jul  7 21:59 core
$ rm -f core; time env CRASHSERVER=/servers/crash-dump-core ./a.out; ls -l core
Aborted (core dumped)
real 1.367 user 0.000 system 0.010
-rw------- 1 tschwinge tschwinge 17031168 Jul  7 22:00 core
$ rm -f core; time env CRASHSERVER=/servers/crash-dump-core ./a.out; ls -l core
Aborted (core dumped)
real 5.789 user 0.000 system 0.010
-rw------- 1 tschwinge tschwinge 17031168 Jul  7 22:00 core
$ rm -f core; time env CRASHSERVER=/servers/crash-dump-core ./a.out; ls -l core
Aborted (core dumped)
real 22.664 user 0.010 system 0.000
-rw------- 1 tschwinge tschwinge 17031168 Jul  7 22:01 core

    • ... produce a huge core file:

      $ du -hs core 
17M     core

      On Linux, the core file occupies 76 KiB of disk space, which seems much more reasonable. This is possibly related with the default 128MiB heap preallocation.

    • ... does not always produce a useful backtrace:

      abort();

      $ gdb test core
warning: core file may not match specified executable file.
[New Thread 86678]
warning: Wrong size fpregset in core file.
...
Core was generated by `./test'.
Program terminated with signal 6, Aborted.
warning: Wrong size fpregset in core file.
(gdb) bt
#0  0x00000000 in ?? ()
#1  0x011f593f in __msg_sig_post (process=72, signal=6, sigcode=0, refport=1)
    at /build/buildd-eglibc_2.10.2-7-hurd-i386-iGL6op/eglibc-2.10.2/build-tree/hurd-i386-libc/hurd/RPC_msg_sig_post.c:144
#2  0x0109a433 in kill_port (pid=<value optimized out>)
    at ../sysdeps/mach/hurd/kill.c:68
#3  kill_pid (pid=<value optimized out>) at ../sysdeps/mach/hurd/kill.c:105
#4  0x0109a69f in __kill (pid=21142, sig=6) at ../sysdeps/mach/hurd/kill.c:139
#5  0x01099af6 in raise (sig=6) at ../sysdeps/posix/raise.c:27
#6  0x0109de59 in abort () at abort.c:88
#7  0x0804849f in main ()

      char *foo = 0; *foo = 1;

      $ gdb test core
Program terminated with signal 11, Segmentation fault.
warning: Wrong size fpregset in core file.
#0  0x00000000 in ?? ()
(gdb) bt
#0  0x00000000 in ?? ()
#1  0x0108565b in __libc_start_main (main=0x8048464 <main>, argc=1, ubp_av=0x1023e64, 
    init=0x8048490 <__libc_csu_init>, fini=0x8048480 <__libc_csu_fini>, rtld_fini=0xea20 <_dl_fini>, 
    stack_end=0x1023e5c) at libc-start.c:251
#2  0x080483d1 in _start ()

      raise (SIGABRT);

      $ gdb a.out core
warning: core file may not match specified executable file.
[New Thread 76651]


warning: Wrong size fpregset in core file.
Reading symbols from /lib/libc.so.0.3...[...]
Core was generated by `./a.out'.
Program terminated with signal 6, Aborted.


warning: Wrong size fpregset in core file.
#0  0x00000000 in ?? ()
(gdb) bt
#0  0x00000000 in ?? ()
Cannot access memory at address 0x17

      Probably GDB doesn't manage to dig in the stack properly.

  • ... against crash-suspend will...

    • ... not work at all:

      $ CRASHSERVER=/servers/crash-suspend ./a.out
$ [returns to the shell and doesn't suspended]

    • ... show big variances in running-time behavior:

      $ TIMEFORMAT='real %R user %U system %S'
$ rm -f core; time env CRASHSERVER=/servers/crash-suspend ./a.out; ls -l core
Aborted (core dumped)
real 1.381 user 0.000 system 0.010
-rw------- 1 tschwinge tschwinge 17031168 Jul  7 22:04 core
$ rm -f core; time env CRASHSERVER=/servers/crash-suspend ./a.out; ls -l core
Aborted (core dumped)
real 1.332 user 0.000 system 0.010
-rw------- 1 tschwinge tschwinge 17031168 Jul  7 22:04 core
$ rm -f core; time env CRASHSERVER=/servers/crash-suspend ./a.out; ls -l core
Aborted (core dumped)
real 21.228 user 0.000 system 0.010
-rw------- 1 tschwinge tschwinge 17031168 Jul  7 22:04 core
$ rm -f core; time env CRASHSERVER=/servers/crash-suspend ./a.out; ls -l core
Aborted (core dumped)
real 1.323 user 0.000 system 0.010
-rw------- 1 tschwinge tschwinge 17031168 Jul  7 22:05 core
$ rm -f core; time env CRASHSERVER=/servers/crash-suspend ./a.out; ls -l core
Aborted (core dumped)
real 22.279 user 0.000 system 0.010
-rw------- 1 tschwinge tschwinge 17031168 Jul  7 22:05 core
$ rm -f core; time env CRASHSERVER=/servers/crash-suspend ./a.out; ls -l core
Aborted (core dumped)
real 1.362 user 0.000 system 0.000
-rw------- 1 tschwinge tschwinge 17031168 Jul  7 22:08 core
$ rm -f core; time env CRASHSERVER=/servers/crash-suspend ./a.out; ls -l core
Aborted (core dumped)
real 21.110 user 0.000 system 0.000
-rw------- 1 tschwinge tschwinge 17031168 Jul  7 22:08 core
$ rm -f core; time env CRASHSERVER=/servers/crash-suspend ./a.out; ls -l core
Aborted (core dumped)
real 1.350 user 0.000 system 0.020
-rw------- 1 tschwinge tschwinge 17031168 Jul  7 22:08 core

    • ... can reliably crash GNU Mach:

      This happens if a core file is already present (and won't get overwritten; see above). I reproduced this three times.

      $ TIMEFORMAT='real %R user %U system %S'
$ time env CRASHSERVER=/servers/crash-suspend ./a.out; ls -l core
Aborted
real 2.856 user 0.000 system 0.010
-rw------- 1 tschwinge tschwinge 17031168 Jul  7 22:08 core


panic: zalloc: zone kalloc.8192 exhausted
Kernel Breakpoint trap, eip 0x20020a77
Stopped at  0x20020a76: int     $3
db> trace
0x20020a76(2006aba8,4d0f7e9c,200209b0,0,0)
0x20020a4d(2006b094,2006ae40,2000,20016803,4a5f4114)
0x2002bca5(49a03564,1,0,9,1000)
0x20022f4c(2000,4a5f45d4,4a84879c,49a46564,4ac43e78)
0x20021e65(4ac43e78,4a5f45d4,4a5f4114,0,0)
0x2005309d(2106ba9c,3,38,28,1783)
Bad frame pointer: 0x2106ba78


$ addr2line -i -f -e /boot/gnumach-xen 0x20020a76 0x20020a4d 0x2002bca5 0x20022f4c 0x20021e65 0x2005309d
Debugger
/home/tschwinge/tmp/gnumach/gnumach-1-branch-Xen-branch.build/../gnumach-1-branch-Xen-branch/kern/debug.c:105
panic
/home/tschwinge/tmp/gnumach/gnumach-1-branch-Xen-branch.build/../gnumach-1-branch-Xen-branch/kern/debug.c:148
zalloc
/home/tschwinge/tmp/gnumach/gnumach-1-branch-Xen-branch.build/../gnumach-1-branch-Xen-branch/kern/zalloc.c:470
kalloc
/home/tschwinge/tmp/gnumach/gnumach-1-branch-Xen-branch.build/../gnumach-1-branch-Xen-branch/kern/kalloc.c:185
ipc_kobject_server
/home/tschwinge/tmp/gnumach/gnumach-1-branch-Xen-branch.build/../gnumach-1-branch-Xen-branch/kern/ipc_kobject.c:76
mach_msg_trap
/home/tschwinge/tmp/gnumach/gnumach-1-branch-Xen-branch.build/../gnumach-1-branch-Xen-branch/ipc/mach_msg.c:1367

If someone is working in this area, they may want to have a look at GDB gcore, and port http://code.google.com/p/google-coredumper/, too.