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diff agent/doc/transported_core.html @ 0:a61af66fc99e jdk7-b24
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author | duke |
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date | Sat, 01 Dec 2007 00:00:00 +0000 |
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--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/agent/doc/transported_core.html Sat Dec 01 00:00:00 2007 +0000 @@ -0,0 +1,110 @@ +<html> +<head> +<title> +Debugging transported core dumps +</title> +</head> +<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> + + +</body> +</html>