gdb - loading symbols of shared library

Paul Pluzhnikov
Sun Oct 12 15:36:00 GMT 2008

On Sun, Oct 12, 2008 at 5:57 AM, rimon <> wrote:
> I am debugging in gdb a program that dynamically loads I want
> to debug the code from libodbcinst - I can break in it, see the source and
> step through it, but whenever I try printing a variable, I get (e.g. for the
> variable ret):
> "No symbol "ret" in current context."

Most often this is the result of being compiled
with 'gcc -g -O2'. Compiler has optimized the variable out.

> In my program loads my own library (an odbc driver). This
> library I can debug fully, symbols and all.

Your own library was compiled without -O*.

> Things I've verified:
> - is compiled with debug information. I compiled it myself
> from UnixODBC sources, and made sure it was compiled with debug info.

You can verify that it was compiled with '-O2 -g', and rebuilt it
with 'CFLAGS=-g -O0'.

> - is not stripped - I ran 'nm' on it, and got a symbol table.
> - From gdb I ran 'info share' and saw that was in the list of
> loaded libraries. I also tried running 'sharedlibrary' but
> this made no difference.
> - I tried running add-symbol-file for the library.

If the library is listed in 'info shared' (which must be true since you can
set breakpoints in it), then GDB has already added it; you don't need
to do that.

> I must admit I have a
> problem here. This command is supposed to receive an 'address' parameter.
> The manual says this should be the address where the library was loaded. How
> do I know that library? I tried putting different things there - for example
> the address of the text segment I got from 'maint info sections', but not
> only could I still not see the symbols, this also screwed up something with
> the rest of the debugging.

Calculation of the address is somewhat complicated,
and adding the library at the wrong address will result in GDB
"loosing" it.

> So, in addition to a solution to show the symbols, I would also be very
> grateful for an explanation of the address parameter for add-symbol-file.
> I'm working on HP-UX 11.23 (Itanium). Using HP gdb (wdb) 5.7 .
> TIA!
> RO
> --
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Paul Pluzhnikov

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