Date: Thu, 1 Feb 2007 08:59:36 -0800 From: "Rao, Nikhil" <nikhil.rao@intel.com> To: <freebsd-amd64@freebsd.org> Subject: RE: Issue with using KGDB for remote debug over serial port Message-ID: <12A5C15467D5B94F8E0FF265D9498ADDEEB999@orsmsx419.amr.corp.intel.com>
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Hi all, =20 I think I have found the cause of the issue - I am not sure if this is the root cause,=20 =20 in http://fxr.watson.org/fxr/source/amd64/include/gdb_machdep.h?v=3DRELENG62= =20 32 <http://fxr.watson.org/fxr/source/amd64/include/gdb_machdep.h?v=3DRELENG6= 2 #L32> #define GDB_BUFSZ <http://fxr.watson.org/fxr/ident?v=3DRELENG62;i=3DGDB_BUFSZ>; 500 =20 needs to be changed to=20 =20 32 <http://fxr.watson.org/fxr/source/amd64/include/gdb_machdep.h?v=3DRELENG6= 2 #L32> #define GDB_BUFSZ <http://fxr.watson.org/fxr/ident?v=3DRELENG62;i=3DGDB_BUFSZ>; 1000 = (Really something greater than 840) =20 As soon as the target-host gdb communication is established the gdb_txbuf char array which is of size GDB_BUFSZ gets written to and the writes overflow to beyond GDB_BUFSZ, this corrupts kernel data structures and causes the crash. My observation is that 840bytes get written to the gdb_txbuf array. =20 if anyone has any feedback, please let me know. =20 thanks, Nikhil ________________________________ From: Rao, Nikhil=20 Sent: Wednesday, January 24, 2007 11:26 AM To: 'freebsd-amd64@freebsd.org' Subject: Issue with using KGDB for remote debug over serial port I am trying to debug an AMD64 kernel over a serial connection. Both the host and the target are running AMD64 6.1 release kernels. =20 Target platform - Dell Precision Workstation 690, (Dual Quad core system with Intel Xeon 1.86 Ghz CPU) Host - XPS 600 Dell - Intel Pentium D 3.00 Ghz CPU =20 The target platform boots a 6.1 release GENERIC AMD64 kernel with makeoptions DEBUG=3D-g, KDB and GDB options enabled and has a serial connection with the host. In device.hints I have set hint.sio0.flags=3D0x80 =20 I am able to enter kgdb using the -d boot option, next I can break on a breakpoint. However when I try to step the debugger, the target gets a page fault in kernel mode. I have attached a log of the kgdb output below. Please let me know if any other info. would be useful to resolve this problem. =20 <cut> [GDB will not be able to debug user-mode threads: /usr/lib/libthread_db.so: Undefined symbol "ps_pglobal_lookup"] <cut> 0xffffffff803ecf8f in kdb_enter (msg=3D0x0) at cpufunc.h:63 63 __asm __volatile("int $3"); Unread portion of the kernel message buffer: Cannot access memory at address 0xf000a8ece001a840 (kgdb) break pmap_pinit0 Breakpoint 1 at 0xffffffff805c4d10: file /usr/src/sys/amd64/amd64/pmap.c, line 1059. (kgdb) c Continuing. [New Thread 0] Program received signal SIGQUIT, Quit. [Switching to Thread 0] pmap_pinit0 (pmap=3D0xffffff0000049d00) at /usr/src/sys/amd64/amd64/pmap.c:1061 1061 PMAP_LOCK_INIT(pmap); (kgdb) break 1066 Breakpoint 2 at 0xffffffff805c4d70: file /usr/src/sys/amd64/amd64/pmap.c, line 1066. (kgdb) c Continuing. Program received signal SIGSYS, Bad system call. 0x0000000000000000 in ?? () (kgdb) bt #0 0x0000000000000000 in ?? () #1 0x0000000000000000 in ?? () (kgdb)
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