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Access a c++ module from Perl

I am using cygwin and perl and trying to access some function from a C++
windows dll. After the first attempt produced a segmentation fault, I tried
to do it step-by-step. I created a dummy function in the dll file:

int TestDLL(int x)
{
    return 1;
}


and put the following code in a perl file:

use strict;
use Win32::API::Prototype;

my $TestDLL = ApiLink("mydll",'I TestDLL(I x)');
 if (not defined $TestDLL) {
 die "Can't import API TestDLL: $! \n";
}
print "ApiLink done\n";

my $xx = 0;
my $return = $TestDLL->Call($xx);
print $return."\n";


But even this produces a segmentation fault (core dump). Any ideas?

BG


0
bg
10/24/2005 3:21:59 PM
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"bg-greece" <temporary@mail.gr> wrote:

> I am using cygwin and perl and trying to access some function from a
> C++ windows dll. After the first attempt produced a segmentation
> fault, I tried to do it step-by-step. I created a dummy function in
> the dll file: 

....
 
> But even this produces a segmentation fault (core dump). Any ideas?

Just a very wild guess: you wrote Cygwin. How did you make the DLL? Inside 
Cygwin, or outside it?

-- 
John                   Small Perl scripts: http://johnbokma.com/perl/
               Perl programmer available:     http://castleamber.com/
                                        I ploink googlegroups.com :-)
                        
0
John
10/24/2005 3:35:12 PM
the dll was created with with Microsoft Visual C++ 6.0


"John Bokma" <john@castleamber.com> wrote in message
news:Xns96F96BB05E958castleamber@130.133.1.4...
> Just a very wild guess: you wrote Cygwin. How did you make the DLL? Inside
> Cygwin, or outside it?
>
> -- 
> John                   Small Perl scripts: http://johnbokma.com/perl/
>                Perl programmer available:     http://castleamber.com/
>                                         I ploink googlegroups.com :-)
>


0
bg
10/25/2005 9:00:46 AM
bg-greece wrote:

>I am using cygwin and perl and trying to access some function from a C++
>windows dll. After the first attempt produced a segmentation fault, I tried
>to do it step-by-step. I created a dummy function in the dll file:
>
>int TestDLL(int x)
>{
>    return 1;
>}
>
>
>and put the following code in a perl file:
>
>use strict;
>use Win32::API::Prototype;
>
>my $TestDLL = ApiLink("mydll",'I TestDLL(I x)');
> if (not defined $TestDLL) {
> die "Can't import API TestDLL: $! \n";
>}

In my experience, the prototype based stuff is very buggy. I've had
nothing but crashes with it. I would skip it and go the oldfashioned raw
way, which always *did* work. Try.

	use Win32::API;
	my $TestDLL = Win32::API->new('mydll', 'TestDLL', 'I', 'I') 
	  or die "Can't load function";

   HTH,
   Bart.
0
Bart
10/25/2005 10:34:39 AM
In fact Win32::API was the first try and it also produced segmentation
fault.Other trivial examples however (with kernel32.dll for example) have
worked.

> In my experience, the prototype based stuff is very buggy. I've had
> nothing but crashes with it. I would skip it and go the oldfashioned raw
> way, which always *did* work. Try.
>
> use Win32::API;
> my $TestDLL = Win32::API->new('mydll', 'TestDLL', 'I', 'I')
>   or die "Can't load function";
>
>    HTH,
>    Bart.


0
bg
10/25/2005 12:42:03 PM
bg-greece wrote:
> the dll was created with with Microsoft Visual C++ 6.0

Are you using the Cygwin distribution of Perl? I think you will find 
that it was _not_ made with Visual C++ V6, but with gcc.

I personally have had good luck with Win32::API, though sometimes it was 
not obvious how to describe the function I wanted to import, and when 
you get the description wrong, you do get segment violations. I do not 
remember using the new, sexy prototype interface, just the old, clunky 
one. See Win32::Process::Info::NT for an example.

Disclaimer: I wrote the cited module. And I never said it was a _good_ 
example.

Tom Wyant
0
harryfmudd
10/25/2005 6:51:59 PM
"bg-greece" <temporary@mail.gr> wrote:

> "John Bokma" <john@castleamber.com> wrote in message
> news:Xns96F96BB05E958castleamber@130.133.1.4...
>> Just a very wild guess: you wrote Cygwin. How did you make the DLL?
>> Inside Cygwin, or outside it?

> the dll was created with with Microsoft Visual C++ 6.0

That might cause the problem(s) you see.

-- 
John                   Small Perl scripts: http://johnbokma.com/perl/
               Perl programmer available:     http://castleamber.com/
                                        I ploink googlegroups.com :-)
                        
0
John
10/26/2005 12:50:31 AM
You mean I should create the DLL with cygwin/gcc?
Putting aside that it needs a lot of time to do the porting, it contradicts
the fact that I can perfectly call Windows system DLL's like user32,
kernel32 and so on using Win32::API.

B.

"John Bokma" <john@castleamber.com> wrote in message
news:Xns96FAC9D803B50castleamber@130.133.1.4...
> "bg-greece" <temporary@mail.gr> wrote:
>
> > "John Bokma" <john@castleamber.com> wrote in message
> > news:Xns96F96BB05E958castleamber@130.133.1.4...
> >> Just a very wild guess: you wrote Cygwin. How did you make the DLL?
> >> Inside Cygwin, or outside it?
>
> > the dll was created with with Microsoft Visual C++ 6.0
>
> That might cause the problem(s) you see.
>
> -- 
> John                   Small Perl scripts: http://johnbokma.com/perl/
>                Perl programmer available:     http://castleamber.com/
>                                         I ploink googlegroups.com :-)
>


0
bg
10/26/2005 11:06:08 AM
bg-greece wrote:
> You mean I should create the DLL with cygwin/gcc?
> Putting aside that it needs a lot of time to do the porting, it contradicts
> the fact that I can perfectly call Windows system DLL's like user32,
> kernel32 and so on using Win32::API.

Well, to be honest I have never done what you're trying to do FROM 
CYGWIN. I also note that someone has, because Win32-Process-Info 1.006 
has a "pass" from Cygwin (see 
http://testers.cpan.org/show/Win32-Process-Info.html).

On the other hand, if you have the calling sequence right (as you say 
you do) and if the version of C doesn't matter (as you say it doesn't), 
then we just proved your code works.

But it doesn't. At this point, I generally ask myself "what is it that I 
know to be true, but which is in fact not true?". The possibilities seem 
to me to be:

1) the calling sequence is in fact coded incorrectly in Perl. I have no 
experience with the prototype version of the interface, but the 
traditional interface call in Bart Lateur's response looks right to me 
given the C signature in your original note, and you say that didn't work.

2) Different compilers _can_ produce different calling sequences, so 
that's what I was focusing on. You say calls to Kernel32 work, which 
suggests that this isn't the problem, but doesn't prove it, since we 
don't know that Kernel32 was written in Visual C++. But we _do_ know 
that Visual C++ can call kernel32.dll. Have you read kernel32.h, and 
made sure your signatures are specified the same way? C++ wants to 
mangle function names (that's how overloading works), and it's possible 
that there is more than one way to handle the call stack. A mangled 
function name would probably result in a failure to import the function, 
but there are probably other things that could go wrong.

3) Something else entirely. Arthur Conan Doyle was wrong when he had 
Sherlock Holmes say something like "When you have eliminated everything 
else, the remaining possibility, however improbable, must be the truth." 
The problem with the Sherlock Holmes approach is that it assumes you 
really know what every single possibility is.

Tom Wyant
0
harryfmudd
10/26/2005 2:45:41 PM
"bg-greece" <temporary@mail.gr> wrote in message
news:djl9aa$16vn$1@ulysses.noc.ntua.gr...
> In fact Win32::API was the first try and it also produced segmentation
> fault.Other trivial examples however (with kernel32.dll for example) have
> worked.
>

Those dll's that are working were built using the stdcall calling
convention. I suggest building your dll using the same calling convention -
there's a command line switch that does that for you. (I think it's '/Gz' -
but check 'cl /?')

There exists somewhere a patched version of Win32::API that will work with
cdecl calling convention, but I don't think that patched version has been
ported to Cygwin.

Cheers,
Rob


0
Sisyphus
10/29/2005 10:49:20 PM
Finally I needed to provide the .DEF file before building the DLL so perl
could see the correct function names (i.e. the ones without "decoration").
Thanx everyone
B.


0
bg
11/4/2005 3:01:44 PM
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