Dynamic loading on Cygwin - status

Dynamic loading on Cygwin - status

[Andrej Borsenkow]

O.K., it almost works :-) It was much easier than I suspected due to the fact,
that you can simply link with DLL - no additional stub library is needed. That
enourmosly simplified makefiles.

There are still some gotchas:

- for dlsym() to find a symbol, it has to explcitly exported. It means, that
module's setup() etc functions are not found. They has to be defined with
__attribute__((__dllexport__)). All exported symbols (that have mod_export)
currently get this automatically.

- external function or variable imported from another module is not considered
a constant on Cygwin (actually, on Windows). Hence, any static initializer
fails, e.g

    BUILTIN("cap",    0, bin_cap,    0,  1, 0, NULL, NULL),

where bin_cap is redefined to bin_notavail that in imported from mail DLL.
This is not just as easy to solve.

- some more Makefiles tweaking is needed; because now modules depend on other
module's DLL, we need rules to rebuild them.

- of course, zsh.dll has to be installed into $(bindir) else it is not found.

But still, I did run Zsh compiled with dynamic loading support :-))) My thanks
to Zefram for excellent build system! (And good configure tests).

-andrej

Have a nice DOS!
B >>

RE: Dynamic loading on Cygwin - status

[Andrej Borsenkow]

>
> - for dlsym() to find a symbol, it has to explcitly exported. It means, that
> module's setup() etc functions are not found. They has to be defined with
> __attribute__((__dllexport__)). All exported symbols (that have mod_export)
> currently get this automatically.
>

dllwrap --export-all-symbols

Do you understand now, why Win32 programs have such a size? :-)

(This is quick fix. As we actually need just four functions in addition to
mod_export'ed, it is better to define additional token that is defined on
Cygwin to __attr...)

> - external function or variable imported from another module is not
> considered
> a constant on Cygwin (actually, on Windows). Hence, any static initializer
> fails, e.g

That is really bad. Alternatives are

- compile such module into main DLL. We may somehow automate it by putting
hint into .mdd file
- pretend itself run-time linker and resolve address itself.
- rewrite zsh in C++ ...


Now I *really* have working Zsh will dynamic loading. Unfortunately,
completion is not really useable without parameters module ... just tried

zmodload zsh/mapfile
vared 'mapfile[init.syms]'

it works!

-andrej

Re: Dynamic loading on Cygwin - status

[Peter Stephenson]

> > - external function or variable imported from another module is not
> > considered
> > a constant on Cygwin (actually, on Windows). Hence, any static initializer
> > fails, e.g
> 
> That is really bad.

Isn't it enough to mark it as __attribute__((dllimport)) in the importing
file (assuming the symbol's exported in the first place, obviously)?

-- 
Peter Stephenson <pws@csr.com>
Cambridge Silicon Radio, Unit 300, Science Park, Milton Road,
Cambridge, CB4 0XL, UK                          Tel: +44 (0)1223 392070

RE: Dynamic loading on Cygwin - status

[Andrej Borsenkow]

>
>
> > > - external function or variable imported from another module is not
> > > considered
> > > a constant on Cygwin (actually, on Windows). Hence, any static
> initializer
> > > fails, e.g
> >
> > That is really bad.
>
> Isn't it enough to mark it as __attribute__((dllimport)) in the importing
                                ^^^^^^^^^^^^^^^^^^^^^^^^^^
> file (assuming the symbol's exported in the first place, obviously)?
>

Exactly THIS makes them non-static. But it is not bad as I thought. We do not
need dllimport declaration for functions. We still do need them for variables.
I'll try it as soon as I have time to see, if some external variable is used
in static context.
(It is clear. In case of variables, compiler actually generates code to call a
function that returns address. Of course, you cannot call function to
intialize static variable. In case of function what gets linked into program
under function's name is a stub that calls "real" function under the name
__imp__<function>. Of course, we can always take an address of this stub - it
is perfectly static).

-andrej