mingw32: .exe -> .a import libs for DLLs?

Peter Dalgaard BSA p.dalgaard@biostat.ku.dk
Sat Jan 17 11:14:00 GMT 1998

Arrrgh. I've been messing around with dlltool and friends all day,
trying to get a DLL to modify a global variable with mingw32, or
rather Werner Koch's cross-development version of it. Basically, I
want to (various bits removed for brevity, so this won't actually run;
dl-routines lifted from Luke Tierney's web page at 
http://www.stat.umn.edu/~luke/xls/projects/dlbasics/dlbasics.html ):


int zip = 0;
void baz(void);

main(int argc, char *argv[])
  void  *libb;
  void (*foo)(void), (*bar)(void);

  libb = dlopen("b.dll", RTLD_NOW);
  bar = dlsym(libb, barsym);
  printf("zip is @%x\n",&zip);
  printf("baz is @%x\n",&baz);


void baz()
  printf("baz called; zip = %d\n", zip);

void bar()
  printf("incrementing zip @%x\n", &zip);
  printf("calling baz @%x\n", &baz);
  printf("done with bar\n");

OK, so I follow the instruction to make b.dll (relocatable, a.m. John
Cerney) and dltest.exe. To access baz and zip, I tried to use the
usual procedure for creating export and import libs for dltest and
linking them into dltest.exe and b.dll, respectively. This works, as
far as loading b.dll and invoking it, but the addresses of zip and baz
are not the same in the two modules, so the zip++ naturally generates
a GPF. Obviously, they aren't getting properly relocated. I think what
I need is a dltest.a with the load addresses hardcoded, but how do I
do that?

Apparently, the commercial compilers know how to do this (nudge,
nudge, know what I mean?) in each their different way.

There are some notes on Fergus's page on building DLL's with gnuwin32,
but quite honestly, I cannot make heads or tails of them...

   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)             FAX: (+45) 35327907

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