Issues with the crash servers.

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+[[!meta copyright="Copyright © 2009 Free Software Foundation, Inc."]]
+
+[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable
+id="license" text="Permission is granted to copy, distribute and/or modify this
+document under the terms of the GNU Free Documentation License, Version 1.2 or
+any later version published by the Free Software Foundation; with no Invariant
+Sections, no Front-Cover Texts, and no Back-Cover Texts.  A copy of the license
+is included in the section entitled [[GNU Free Documentation
+License|/fdl]]."]]"""]]
+
+[[!tag open_issue_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.
+
+      * ... produce an invalid `core` file:
+
+            $ 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
+
+        [[!tag open_issue_gdb]] Probably the `crash` server code and [[GDB]] are
+        out of sync.
+
+  * ... 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