How to handle variables (data, etc.) in DLLs?

How to handle variables (data, etc.) in DLLs?

[T J Harding]

Hi

I was porting something to Cygwin and all was going swimmingly, until I
ran into problems building a DLL from object code with global data
symbols (i.e.
nm shows these symbols as type D or C).

Just to make it clearer, a trivial example:

main.c might contain:

extern int foo;
extern void bar(void);
int main ( int argc, char **argv )
{
  foo++;
  bar();
}

and foo.c might contain:

int foo=0;
void bar(void)
{
  foo--;
}

It is foo.o that I want to include in a DLL.

I was using dllwrap 0.2.4 (and dlltool 2.9.4) with b20.1 (95 and NT).
"dllwrap --export-all-symbols" exports the data symbols to the .def
file, but
they seem to be exported as if they were functions, resulting in a core
dump
when a.exe is run.  I've tried putting "DATA" after the symbol name in
the
.def file, which results in the symbol being undefined in the import-lib
libfoo.a, meaning I have to link foo.o in as well as libfoo.a.

So how should one best deal with this situation?  It's not my code, so I
don't 
want to have to alter it significantly just to port it.

Tim
begin:vcard 
n:Harding;Tim
tel;cell:+44 961 444986
tel;fax:+44 131 220 4492
tel;work:+44 131 220 4491
x-mozilla-html:TRUE
url:www.quadstone.com
org:Quadstone
adr:;;16 Chester Street;Edinburgh;Scotland;EH3 7RA;United Kingdom
version:2.1
email;internet:tjh@quadstone.com
title:Decisionhouse Services
x-mozilla-cpt:;-1080
fn:Tim Harding
end:vcard

Re: How to handle variables (data, etc.) in DLLs?

[DJ Delorie]

DLLs *can't* export "data".  They can only export pointers to data,
which is what they do.  In older gccs, you'll need to do something
like this:

extern int *__imp_foo;
#define foo (*__imp_foo)

In newer gccs, do something like this:

extern int foo __attribute__((dllimport));

These tell gcc to dereference the imported pointer, rather than
thinking it's the data itself.

--
Want to unsubscribe from this list?
Send a message to cygwin-unsubscribe@sourceware.cygnus.com

Re: How to handle variables (data, etc.) in DLLs?

[T J Harding]

DJ Delorie wrote:

> DLLs *can't* export "data".  They can only export pointers to data,
> which is what they do.  In older gccs, you'll need to do something
> like this:
> 
> extern int *__imp_foo;
> #define foo (*__imp_foo)
> 
> In newer gccs, do something like this:
> 
> extern int foo __attribute__((dllimport));
> 
> These tell gcc to dereference the imported pointer, rather than
> thinking it's the data itself.

Thanks, that's useful to know (although there are about 250 of these
data symbols in the code!).  I'd need to brush up on my C++ (yes, this
is actually C++ code) to figure out what's required.

Tim
begin:vcard 
n:Harding;Tim
tel;cell:+44 961 444986
tel;fax:+44 131 220 4492
tel;work:+44 131 220 4491
x-mozilla-html:TRUE
url:www.quadstone.com
org:Quadstone
adr:;;16 Chester Street;Edinburgh;Scotland;EH3 7RA;United Kingdom
version:2.1
email;internet:tjh@quadstone.com
title:Decisionhouse Services
x-mozilla-cpt:;-1080
fn:Tim Harding
end:vcard

Re: How to handle variables (data, etc.) in DLLs?

[Mikey]

yourfile.h
#define extern __attribute__((dllimport))
extern int yourdata_in_dll;
#undef extern

not sure about egcs-1.1 but 1.1.1 this will work.

On Thu, 04 Mar 1999 09:31:53 +0000, you wrote:

>DJ Delorie wrote:
>
>> DLLs *can't* export "data".  They can only export pointers to data,
>> which is what they do.  In older gccs, you'll need to do something
>> like this:
>> 
>> extern int *__imp_foo;
>> #define foo (*__imp_foo)
>> 
>> In newer gccs, do something like this:
>> 
>> extern int foo __attribute__((dllimport));
>> 
>> These tell gcc to dereference the imported pointer, rather than
>> thinking it's the data itself.
>
>Thanks, that's useful to know (although there are about 250 of these
>data symbols in the code!).  I'd need to brush up on my C++ (yes, this
>is actually C++ code) to figure out what's required.
>
>Tim


--
Want to unsubscribe from this list?
Send a message to cygwin-unsubscribe@sourceware.cygnus.com

Re: How to handle variables (data, etc.) in DLLs?

[Mikey]

yourfile.h
#define extern __attribute__((dllimport))
extern int yourdata_in_dll;
#undef extern

not sure about egcs-1.1 but 1.1.1 this will work.

On Thu, 04 Mar 1999 09:31:53 +0000, you wrote:

>DJ Delorie wrote:
>
>> DLLs *can't* export "data".  They can only export pointers to data,
>> which is what they do.  In older gccs, you'll need to do something
>> like this:
>> 
>> extern int *__imp_foo;
>> #define foo (*__imp_foo)
>> 
>> In newer gccs, do something like this:
>> 
>> extern int foo __attribute__((dllimport));
>> 
>> These tell gcc to dereference the imported pointer, rather than
>> thinking it's the data itself.
>
>Thanks, that's useful to know (although there are about 250 of these
>data symbols in the code!).  I'd need to brush up on my C++ (yes, this
>is actually C++ code) to figure out what's required.
>
>Tim


--
Want to unsubscribe from this list?
Send a message to cygwin-unsubscribe@sourceware.cygnus.com

How to handle variables (data, etc.) in DLLs?

[T J Harding]

Hi

I was porting something to Cygwin and all was going swimmingly, until I
ran into problems building a DLL from object code with global data
symbols (i.e.
nm shows these symbols as type D or C).

Just to make it clearer, a trivial example:

main.c might contain:

extern int foo;
extern void bar(void);
int main ( int argc, char **argv )
{
  foo++;
  bar();
}

and foo.c might contain:

int foo=0;
void bar(void)
{
  foo--;
}

It is foo.o that I want to include in a DLL.

I was using dllwrap 0.2.4 (and dlltool 2.9.4) with b20.1 (95 and NT).
"dllwrap --export-all-symbols" exports the data symbols to the .def
file, but
they seem to be exported as if they were functions, resulting in a core
dump
when a.exe is run.  I've tried putting "DATA" after the symbol name in
the
.def file, which results in the symbol being undefined in the import-lib
libfoo.a, meaning I have to link foo.o in as well as libfoo.a.

So how should one best deal with this situation?  It's not my code, so I
don't 
want to have to alter it significantly just to port it.

Tim
begin:vcard 
n:Harding;Tim
tel;cell:+44 961 444986
tel;fax:+44 131 220 4492
tel;work:+44 131 220 4491
x-mozilla-html:TRUE
url:www.quadstone.com
org:Quadstone
adr:;;16 Chester Street;Edinburgh;Scotland;EH3 7RA;United Kingdom
version:2.1
email;internet:tjh@quadstone.com
title:Decisionhouse Services
x-mozilla-cpt:;-1080
fn:Tim Harding
end:vcard

Re: How to handle variables (data, etc.) in DLLs?

[T J Harding]

DJ Delorie wrote:

> DLLs *can't* export "data".  They can only export pointers to data,
> which is what they do.  In older gccs, you'll need to do something
> like this:
> 
> extern int *__imp_foo;
> #define foo (*__imp_foo)
> 
> In newer gccs, do something like this:
> 
> extern int foo __attribute__((dllimport));
> 
> These tell gcc to dereference the imported pointer, rather than
> thinking it's the data itself.

Thanks, that's useful to know (although there are about 250 of these
data symbols in the code!).  I'd need to brush up on my C++ (yes, this
is actually C++ code) to figure out what's required.

Tim
begin:vcard 
n:Harding;Tim
tel;cell:+44 961 444986
tel;fax:+44 131 220 4492
tel;work:+44 131 220 4491
x-mozilla-html:TRUE
url:www.quadstone.com
org:Quadstone
adr:;;16 Chester Street;Edinburgh;Scotland;EH3 7RA;United Kingdom
version:2.1
email;internet:tjh@quadstone.com
title:Decisionhouse Services
x-mozilla-cpt:;-1080
fn:Tim Harding
end:vcard

Re: How to handle variables (data, etc.) in DLLs?

[DJ Delorie]

DLLs *can't* export "data".  They can only export pointers to data,
which is what they do.  In older gccs, you'll need to do something
like this:

extern int *__imp_foo;
#define foo (*__imp_foo)

In newer gccs, do something like this:

extern int foo __attribute__((dllimport));

These tell gcc to dereference the imported pointer, rather than
thinking it's the data itself.

--
Want to unsubscribe from this list?
Send a message to cygwin-unsubscribe@sourceware.cygnus.com