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| <title> |
| Debugging transported core dumps |
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| <body> |
| <h1>Debugging transported core dumps</h1> |
| |
| <p> |
| When a core dump is moved to a machine different from the one where it was |
| produced ("transported core dump"), debuggers (dbx, gdb, windbg or SA) do not |
| always successfully open the dump. This is due to kernel, library (shared |
| objects or DLLs) mismatch between core dump machine and debugger machine. |
| </p> |
| |
| <p> |
| In most platforms, core dumps do not contain text (a.k.a) Code pages. |
| There pages are to be read from executable and shared objects (or DLLs). |
| Therefore it is important to have matching executable and shared object |
| files in debugger machine. |
| </p> |
| |
| <h3>Solaris transported core dumps</h3> |
| |
| <p> |
| Debuggers on Solaris (and Linux) use two addtional shared objects |
| <b>rtld_db.so</b> and <b>libthread_db.so</b>. rtld_db.so is used to |
| read information on shared objects from the core dump. libthread_db.so |
| is used to get information on threads from the core dump. rtld_db.so |
| evolves along with rtld.so (the runtime linker library) and libthread_db.so |
| evolves along with libthread.so (user land multithreading library). |
| Hence, debugger machine should have right version of rtld_db.so and |
| libthread_db.so to open the core dump successfully. More details on |
| these debugger libraries can be found in |
| <a href="http://docs.sun.com/app/docs/doc/817-1984/"> |
| Solaris Linkers and Libraries Guide - 817-1984</a> |
| </p> |
| |
| <h3>Solaris SA against transported core dumps</h3> |
| |
| <p> |
| With transported core dumps, you may get "rtld_db failures" or |
| "libthread_db failures" or SA may just throw some other error |
| (hotspot symbol is missing) when opening the core dump. |
| Enviroment variable <b>LIBSAPROC_DEBUG</b> may be set to any value |
| to debug such scenarios. With this env. var set, SA prints many |
| messages in standard error which can be useful for further debugging. |
| SA on Solaris uses <b>libproc.so</b> library. This library also |
| prints debug messages with env. var <b>LIBPROC_DEBUG</b>. But, |
| setting LIBSAPROC_DEBUG results in setting LIBPROC_DEBUG as well. |
| </p> |
| <p> |
| The best possible way to debug a transported core dump is to match the |
| debugger machine to that of core dump machine. i.e., have same Kernel |
| and libthread patch level between the machines. mdb (Solaris modular |
| debugger) may be used to find the Kernel patch level of core dump |
| machine and debugger machine may be brought to the same level. |
| </p> |
| <p> |
| If the matching machine is "far off" in your network, then |
| <ul> |
| <li>consider using rlogin and <a href="clhsdb.html">CLHSDB - SA command line HSDB interface</a> or |
| <li>use SA remote debugging and debug the core from core machine remotely. |
| </ul> |
| </p> |
| |
| <p> |
| But, it may not be feasible to find matching machine to debug. |
| If so, you can copy all application shared objects (and libthread_db.so, if needed) from the core dump |
| machine into your debugger machine's directory, say, /export/applibs. Now, set <b>SA_ALTROOT</b> |
| environment variable to point to /export/applibs directory. Note that /export/applibs should either |
| contain matching 'full path' of libraries. i.e., /usr/lib/libthread_db.so from core |
| machine should be under /export/applibs/use/lib directory and /use/java/jre/lib/sparc/client/libjvm.so |
| from core machine should be under /export/applibs/use/java/jre/lib/sparc/client so on or /export/applibs |
| should just contain libthread_db.so, libjvm.so etc. directly. |
| </p> |
| |
| <p> |
| Support for transported core dumps is <b>not</b> built into the standard version of libproc.so. You need to |
| set <b>LD_LIBRARY_PATH</b> env var to point to the path of a specially built version of libproc.so. |
| Note that this version of libproc.so has a special symbol to support transported core dump debugging. |
| In future, we may get this feature built into standard libproc.so -- if that happens, this step (of |
| setting LD_LIBRARY_PATH) can be skipped. |
| </p> |
| |
| <h3>Ignoring libthread_db.so failures</h3> |
| <p> |
| If you are okay with missing thread related information, you can set |
| <b>SA_IGNORE_THREADDB</b> environment variable to any value. With this |
| set, SA ignores libthread_db failure, but you won't be able to get any |
| thread related information. But, you would be able to use SA and get |
| other information. |
| </p> |
| |
| <h3>Linux SA against transported core dumps</h3> |
| <p> |
| On Linux, SA parses core and shared library ELF files. SA <b>does not</b> use |
| libthread_db.so or rtld_db.so for core dump debugging (although |
| libthread_db.so is used for live process debugging). But, you |
| may still face problems with transported core dumps, because matching shared |
| objects may not be in the path(s) specified in core dump file. To |
| workaround this, you can define environment variable <b>SA_ALTROOT</b> |
| to be the directory where shared libraries are kept. The semantics of |
| this env. variable is same as that for Solaris (please refer above). |
| </p> |
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