[fpc-pascal] Linking to C++ DLL compiled with MSVC

[Michael Lutz]

I've been trying to link to an external DLL which is unfortunately
compiled using MSVC in C++ mode. The functions itself do not use any C++
features, they are just not declared as extern "C" and thus use name mangling.

With MSVC name mangling, each symbol starts with a '?' character, which
seems to not play well with fpc in some situations. Below are two test
cases, where the first one works and the second one fails. If I remove the
'?' from the external name, both test cases compile and produce an EXE
with the proper imports.

Unfortunately, the second one is the interesting one as not using units is
no option. Is this is a genuine bug or is a symbol containing a '?' not
supported in units by design?

$ cat test.pas
program Test;

procedure Dummy; external 'who_cares' name '?Dummy';

begin
  Dummy;
end.

$ fpc test.pas
Free Pascal Compiler version 2.4.4 [2011/09/29] for x86_64
Copyright (c) 1993-2010 by Florian Klaempfl
Target OS: Win64 for x64
Compiling test.pas
Linking test.exe
7 lines compiled, 0.1 sec , 32464 bytes code, 1664 bytes data



$ cat test2.pas
program Test2;

uses TestUnit;

begin
  Dummy;
end.

$ cat testunit.pas
unit TestUnit;

interface

procedure Dummy;

implementation

procedure Dummy; external 'who_cares' name '?Dummy';

end.

$ fpc test2.pas
Free Pascal Compiler version 2.4.4 [2011/09/29] for x86_64
Copyright (c) 1993-2010 by Florian Klaempfl
Target OS: Win64 for x64
Compiling test2.pas
Compiling testunit.pas
Linking test2.exe
test2.pas(7,1) Error: Undefined symbol: ?Dummy
test2.pas(7,1) Fatal: There were 1 errors compiling module, stopping
Fatal: Compilation aborted