python config question

python config question

[Michael Snyder]

Question about --with-python=$PATH.

If I have python version X installed "natively" on my build machine
(eg. at /usr/lib/libpython.*), and version Y installed somewhere else
(eg. at $PYPATH), and I tell configure that I want to use the one at
$PYPATH, eg.

     configure --with-python=$PYPATH

Shouldn't I expect gdb to be linked against python version Y?

That doesn't seem to be what happens, in fact "ldd" tells me
that gdb wants to use version X at /usr/lib/libpython*.

Re: python config question

[Joel Brobecker]

>     configure --with-python=$PYPATH
> 
> Shouldn't I expect gdb to be linked against python version Y?

I would think so. But from what I can tell by looking at the configury,
I think that your GDB was in fact linked against the Python install
that you provided (using -L${with_python}/lib in the link command).
However, your loader is selecting the libpython in your default install
because it does not know about you local one. You have several solutions
to fix this, typical ones being: use th rpath during the link, or
add your python install lib dir to LD_LIBRARY_PATH, for instance.

-- 
Joel

Re: python config question

[Michael Snyder]

Joel Brobecker wrote:
>>     configure --with-python=$PYPATH
>>
>> Shouldn't I expect gdb to be linked against python version Y?
> 
> I would think so. But from what I can tell by looking at the configury,
> I think that your GDB was in fact linked against the Python install
> that you provided (using -L${with_python}/lib in the link command).
> However, your loader is selecting the libpython in your default install
> because it does not know about you local one. You have several solutions
> to fix this, typical ones being: use th rpath during the link, or
> add your python install lib dir to LD_LIBRARY_PATH, for instance.
> 

Maybe the configure option should include rpath?

Re: python config question

[Joel Brobecker]

> Maybe the configure option should include rpath?

It could.  We're touching at something that is very platform-dependent,
though - perhaps you want to look at using libtool (although I'll admit
to a severe aversion to this tool, probably unjustified). If I were in
your position, I might consider linking statically against libpython.
At AdaCore, the plan is to use LD_LIBRARY_PATH, which we'll have to do,
since customers are free to install the binary package wherever they
want (hence preventing rpath from working).

-- 
Joel

Re: python config question

[Jan Kratochvil]

On Wed, 03 Mar 2010 05:50:39 +0100, Joel Brobecker wrote:
> > Maybe the configure option should include rpath?
> 
> It could.  We're touching at something that is very platform-dependent,
> though - perhaps you want to look at using libtool (although I'll admit
> to a severe aversion to this tool, probably unjustified). If I were in
> your position, I might consider linking statically against libpython.
> At AdaCore, the plan is to use LD_LIBRARY_PATH, which we'll have to do,
> since customers are free to install the binary package wherever they
> want (hence preventing rpath from working).

IIUC you ship libpython*.so.* libraries bundled with the shipped gdb.
Isn't ld.so's $ORIGIN useful?

$ORIGIN and rpath
	ld.so understands the string $ORIGIN (or equivalently ${ORIGIN}) in an
	rpath specification (DT_RPATH or DT_RUNPATH) to mean the directory
	containing the application executable.  Thus, an application located
	in somedir/app could be compiled with gcc -Wl,-rpath,'$ORIGIN/../lib'
	so that it finds an associated shared library in somedir/lib no matter
	where somedir is located in the directory hierarchy.  This facilitates
	the creation of "turn-key" applications that do not need to be
	installed into special directories, but can instead be unpacked into
	any directory and still find their own shared libraries.


Regards,
Jan

Re: python config question

[Joel Brobecker]

> IIUC you ship libpython*.so.* libraries bundled with the shipped gdb.
> Isn't ld.so's $ORIGIN useful?

Yep - very useful (in fact, I had forgotten about this already).
I just wanted to give Michael some of the standard options to deal
with his situation...

-- 
Joel

Re: python config question

[Daniel Jacobowitz]

On Wed, Mar 03, 2010 at 10:20:47AM +0100, Jan Kratochvil wrote:
> IIUC you ship libpython*.so.* libraries bundled with the shipped gdb.
> Isn't ld.so's $ORIGIN useful?
> 
> $ORIGIN and rpath

FYI, this is how we do it, and part of why I don't think automatic
-rpath is a good idea.

-- 
Daniel Jacobowitz
CodeSourcery

Re: python config question

[Michael Snyder]

Daniel Jacobowitz wrote:
> On Wed, Mar 03, 2010 at 10:20:47AM +0100, Jan Kratochvil wrote:
>> IIUC you ship libpython*.so.* libraries bundled with the shipped gdb.
>> Isn't ld.so's $ORIGIN useful?
>>
>> $ORIGIN and rpath
> 
> FYI, this is how we do it, and part of why I don't think automatic
> -rpath is a good idea.

You're saying that you ship the python library, install it in the
same directory as gdb, and get the runtime loader to look for it there?

Re: python config question

[Daniel Jacobowitz]

On Wed, Mar 03, 2010 at 09:46:12AM -0800, Michael Snyder wrote:
> You're saying that you ship the python library, install it in the
> same directory as gdb, and get the runtime loader to look for it there?

It goes in $ORIGIN/../lib/ actually, but yes.

-- 
Daniel Jacobowitz
CodeSourcery