Re: [HTCondor-devel] [htcondor-fw] debug/stripped/unstripped binaries. didn't work, need help.

[Todd Tannenbaum <tannenba@xxxxxxxxxxx>]

[conversation moved from htcondor-fw to htcondor-devel]

Given all the below is now getting quite involved, is it time we made a 
debug symbols package for HTCondor?  We used to create one (or at least 
a debug symbols tarball), it disappeared when we moved to cmake.
regards,
Todd


On 12/7/2012 4:28 PM, Zachary Miller wrote:
> On Mon, Dec 03, 2012 at 07:47:34PM -0600, Todd Tannenbaum wrote:
> > Say you have a.out.stripped and a.out.with_symbols.  And say you have a
> > core file from a.out.stripped.  The trick is you still want to gdb the
> > file that produced the core, but load symbols from the unstripped binary
> > into the text segment of the file you are debugging.
> >
> > % gdb a.out.stripped core
> >    ... gdb will complain about missing debug info ...
> >
> > (gdb) maint info sections     <--- enter this command
> >
> > In the output from 'maint info sections', look for .text section. The
> > address that is in the first column is what you want to use in the next
> > command.  For instance, one of the output lines from 'maint info
> > sections' will be
> >
> >    0x00400390->0x00400588 at 0x00000390: .text ALLOC LOAD READONLY CODE
> > HAS_CONTENTS
> >
> > The address in the first column, 0x00400390 in this example, is used in
> > the next gdb command:
> >
> > (gdb) add-symbol-file a.out.with_symbols 0x00400390
> >
> > Of course, substitute 0x00400390 with the proper text segment address.
> >
> > Now you should be able to do a backtrace, etc.
> That will get your symbols loaded for the main executable, but you still won't
> have any symbols for libraries that were dynamically loaded, which these days
> is most of HTCondor.
>
> So, to get those, you need to do a couple things.
>
> First, run gdb on the unstripped version of the .so you would like to load and
> find the .text segment just like above, and write down the offset (the first
> column), you'll need it later.
>
> Second, go back to gdb with the stripped binary and the core. If you look at
> any particular stack frame, you'll see the instruction pointer in the second
> column:
>
>      #7  0x00007f034f8c1834 in KeyCache::remove ()
>
> Now comes the black-magic portion. Run "maint info sections" again and look at
> the first column. Find the entry that contains the above instruction pointer.
> It should be marked "ALLOC READONLY CODE". Now, add that address to the offset
> of the .text segment from the .so file you found above. Finally, you can add
> the symbols from the shared library with
>
>      add-symbol-file unstripped.so 0xMagicAddress
>
> You'll have to do this for each shared library (libcondor_util, libclassad,
> etc.) if you need the symbols for that particular stack frame.
>
>
> > Note: I added the above wisdom to
> >     https://htcondor-wiki.cs.wisc.edu/index.cgi/wiki?p=DaemonDebugging
> > Feel free to improve it.
> i did.
>
>
> cheers,
> -zach

--
Todd Tannenbaum <tannenba@xxxxxxxxxxx> University of Wisconsin-Madison
Center for High Throughput Computing   Department of Computer Sciences
HTCondor Technical Lead                1210 W. Dayton St. Rm #4257
Phone: (608) 263-7132                  Madison, WI 53706-1685