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2 <head>
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3 <title>
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4 Debugging transported core dumps
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5 </title>
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6 </head>
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7 <body>
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8 <h1>Debugging transported core dumps</h1>
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9
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10 <p>
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11 When a core dump is moved to a machine different from the one where it was
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12 produced ("transported core dump"), debuggers (dbx, gdb, windbg or SA) do not
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13 always successfully open the dump. This is due to kernel, library (shared
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14 objects or DLLs) mismatch between core dump machine and debugger machine.
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15 </p>
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16
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17 <p>
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18 In most platforms, core dumps do not contain text (a.k.a) Code pages.
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19 There pages are to be read from executable and shared objects (or DLLs).
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20 Therefore it is important to have matching executable and shared object
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21 files in debugger machine.
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22 </p>
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23
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24 <h3>Solaris transported core dumps</h3>
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25
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26 <p>
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27 Debuggers on Solaris (and Linux) use two addtional shared objects
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28 <b>rtld_db.so</b> and <b>libthread_db.so</b>. rtld_db.so is used to
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29 read information on shared objects from the core dump. libthread_db.so
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30 is used to get information on threads from the core dump. rtld_db.so
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31 evolves along with rtld.so (the runtime linker library) and libthread_db.so
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32 evolves along with libthread.so (user land multithreading library).
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33 Hence, debugger machine should have right version of rtld_db.so and
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34 libthread_db.so to open the core dump successfully. More details on
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35 these debugger libraries can be found in
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36 <a href="http://docs.sun.com/app/docs/doc/817-1984/">
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37 Solaris Linkers and Libraries Guide - 817-1984</a>
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38 </p>
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39
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40 <h3>Solaris SA against transported core dumps</h3>
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41
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42 <p>
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43 With transported core dumps, you may get "rtld_db failures" or
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44 "libthread_db failures" or SA may just throw some other error
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45 (hotspot symbol is missing) when opening the core dump.
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46 Enviroment variable <b>LIBSAPROC_DEBUG</b> may be set to any value
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47 to debug such scenarios. With this env. var set, SA prints many
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48 messages in standard error which can be useful for further debugging.
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49 SA on Solaris uses <b>libproc.so</b> library. This library also
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50 prints debug messages with env. var <b>LIBPROC_DEBUG</b>. But,
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51 setting LIBSAPROC_DEBUG results in setting LIBPROC_DEBUG as well.
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52 </p>
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53 <p>
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54 The best possible way to debug a transported core dump is to match the
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55 debugger machine to that of core dump machine. i.e., have same Kernel
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56 and libthread patch level between the machines. mdb (Solaris modular
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57 debugger) may be used to find the Kernel patch level of core dump
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58 machine and debugger machine may be brought to the same level.
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59 </p>
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60 <p>
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61 If the matching machine is "far off" in your network, then
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62 <ul>
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63 <li>consider using rlogin and <a href="clhsdb.html">CLHSDB - SA command line HSDB interface</a> or
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64 <li>use SA remote debugging and debug the core from core machine remotely.
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65 </ul>
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66 </p>
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67
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68 <p>
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69 But, it may not be feasible to find matching machine to debug.
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70 If so, you can copy all application shared objects (and libthread_db.so, if needed) from the core dump
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71 machine into your debugger machine's directory, say, /export/applibs. Now, set <b>SA_ALTROOT</b>
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72 environment variable to point to /export/applibs directory. Note that /export/applibs should either
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73 contain matching 'full path' of libraries. i.e., /usr/lib/libthread_db.so from core
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74 machine should be under /export/applibs/use/lib directory and /use/java/jre/lib/sparc/client/libjvm.so
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75 from core machine should be under /export/applibs/use/java/jre/lib/sparc/client so on or /export/applibs
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76 should just contain libthread_db.so, libjvm.so etc. directly.
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77 </p>
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78
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79 <p>
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80 Support for transported core dumps is <b>not</b> built into the standard version of libproc.so. You need to
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81 set <b>LD_LIBRARY_PATH</b> env var to point to the path of a specially built version of libproc.so.
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82 Note that this version of libproc.so has a special symbol to support transported core dump debugging.
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83 In future, we may get this feature built into standard libproc.so -- if that happens, this step (of
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84 setting LD_LIBRARY_PATH) can be skipped.
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85 </p>
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86
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87 <h3>Ignoring libthread_db.so failures</h3>
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88 <p>
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89 If you are okay with missing thread related information, you can set
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90 <b>SA_IGNORE_THREADDB</b> environment variable to any value. With this
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91 set, SA ignores libthread_db failure, but you won't be able to get any
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92 thread related information. But, you would be able to use SA and get
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93 other information.
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94 </p>
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95
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96 <h3>Linux SA against transported core dumps</h3>
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97 <p>
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98 On Linux, SA parses core and shared library ELF files. SA <b>does not</b> use
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99 libthread_db.so or rtld_db.so for core dump debugging (although
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100 libthread_db.so is used for live process debugging). But, you
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101 may still face problems with transported core dumps, because matching shared
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102 objects may not be in the path(s) specified in core dump file. To
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103 workaround this, you can define environment variable <b>SA_ALTROOT</b>
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104 to be the directory where shared libraries are kept. The semantics of
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105 this env. variable is same as that for Solaris (please refer above).
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106 </p>
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107
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108
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109 </body>
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110 </html>
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