Jeffrey Holle <jeff.holle@xxxxxxxxxxx> writes:
> The program uses a shared library which I have constructed.
> This library in turn uses boost.python and the Python C API.
>
> The link errors all concern functions from the later, which start with "Py".
>
> First question.
> Is it normal that a cpp client of a shared library share the resource
> requirements of the shared library?
It would help enormously if you posted the exact error you are
getting, rather than paraphrase it. Please try to be specific in bug
reports.
So I'm not sure I understand the question, but I'll take a stab at it.
When you run a program, all the symbol references should normally be
resolved somewhere. The linker tries to help you out by
double-checking this at link time. It essentially emulates the search
done by the dynamic linker to make sure that all symbols are defined.
In the CVS version of the linker there is an option to control this:
--unresolved-symbols. It's probably not in your version of the
linker, though. I can't remember whether there was another way to
control this in older versions.
Anyhow, the sort of error I am talking about, which looks like
warning: SYM, needed by FILE, not found (try using -rpath or -rpath-link)
does not imply that the client of the shared library shares the
resource requirements of the shared library. It implies that when you
run the program, there is a good chance that it will fail, because SYM
will not be defined. But if you arrange to use the right shared
libraries, or in cases of lazy binding carefully avoid calling
functions which are not defined, then the program may well succeed.
> What is the difference between "normal" symbols and dynamic symbols?
> The later are obtainable from a library using the "--dynamic" option
> of the nm utility.
The normal symbol table is a complete list of the symbols in a
program, modulo whatever strip options you use.
The dynamic symbol table is used by the dynamic linker to resolve
dynamic references. Only symbols which the dynamic linker needs to
see are put into the dynamic symbol table. The dynamic symbol table
is loaded into memory at run time so that the dynamic linker can see
it.
> I've constructed a script that utilizes nm to find library modules
> defining specific symbols. It is:
> #!/bin/sh
> # Find the shared libraries that define specific symbol
> # arg 1 - the root directory from which to search
> # arg 2 - the library name(s) to search for
> # arg 3 - the symbol to search for.
> find $1 -name "$2" -exec nm --print-file-name '{}' ';' | grep " [^
> U] ""$3"
>
> Third question
> Note the use of [ ^ U]. This matches only lines from nm that
> represent references of the symbols. I'm not sure that is what I
> want. I wish to find only symbols that lead to resolution of my
> linker errors. Should I instead by search for a specific type, maybe
> like "D"?
As you say, U means that the symbol is not defined, and is thus
effectively a reference to the symbol. If you are looking for where
the symbol is defined, then use nm --defined-only. If you are looking
for definitions which the dynamic linker will see, then add --dynamic.
(Also I would suggest xargs rather than find -exec.)
Ian
