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<H2><A NAME="SECTION04132000000000000000"></A>
<A NAME="11198"></A><A NAME="11199"></A>
<BR>
Tracking Down Problems
</H2>
<P>
When tracking down problems with Babel libraries, to UNIX tools <TT><B>nm</B></TT> and
<TT><B>ldd</B></TT> are your friends. <TT><B>nm</B></TT> will print the list of linker symbols
in a file, including details such as whether the symbol is defined or not.
<TT><B>ldd</B></TT> lists dynamic dependencies of a shared libraries or executables, indicating
where it will look for these symbols when loaded.
<P>
Recall the Fortran hello world example in section <A HREF="node190.html#ss:compilebootcamp">14.2.1</A>. Even though
we may think this is all done with static linking, using these tools we find out the truth.
<P>
<BLOCKQUOTE>
<TT> <TT>%</TT> <TT><B>ldd a.out</B></TT>
<BR> libg2c.so.0 => /usr/local/gcc/3.2/lib/libg2c.so.0 (0x400180000)
<BR> libm.so.6 => /lib/i686/libm.so.6 (0x4004a000)
<BR> libgcc_s.so.1 => //usr/local/gcc/3.2/lib/libgcc_s.so.1 (0x4006d000)
<BR> libc.so.6 => /lib/i686/libc.so.6 (0x40076000)
<BR> /lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000)
<BR>
</TT></BLOCKQUOTE>
<P>
Here, we clearly see that five libraries are shared libraries that will be loaded
after the executable is invoked, but before we get to the main program.
Some of these libraries make sense: <TT>libg2c</TT> is a Fortran to C support library,
<TT>libc</TT> is the C standard library, but why is <TT>libm</TT> listed... its a
library of transcendental functions (e.g. sin(), cos()) why would it be included?
The answer becomes obvious when using ldd on <TT>libg2c</TT>. The fortran support
library has dependencies on the math library, so our FORTRAN executable inherits
that dependency too.
<P>
<BLOCKQUOTE>
<TT> <TT>%</TT> <TT><B>nm a.out | grep ' U '</B></TT>
<BR> U __cxa_atexit@@GLIBC_2.1.3
<BR> U __libc_start_main@@GLIBC_2.0
<BR> U do_lio
<BR> U e_wsle
<BR> U exit@@GLIBC_2.0
<BR> U f_exit
<BR> U f_init
<BR> U f_setarg
<BR> U f_setsig
<BR> U s_stop
<BR> U s_wsle
</TT></BLOCKQUOTE>
<P>
<TT><B>nm</B></TT> (and grep) shows us 11 symbols that are were left undefined in our
final hello world application. A little more nm|greping about will help us find that
symbols starting with <TT>f_</TT> are defined in libg2c.
<P>
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<br><br>babel-0.10.2<br>users_guide Last Modified 2005-03-23<br><br><a href="http://www.llnl.gov/CASC/components">http://www.llnl.gov/CASC/components</a><br><a href="mailto:components@llnl.gov">components@llnl.gov</a>
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