[fpc-devel]Again about calling conventions and name mangling

[Pavel V. Ozerski]

Hello Peter and all FPC team,
Did you look at my $calling patch?

Maybe, I should fix or improve something in it? Or you needs some my
commentaries?
Btw, I'm not sure that general parsing of procedure directives in FPC
is good. There are exist also some differences between FPC and Delphi.
This example can be compiled with Delphi 3 but not with FPC:

{$ifdef fpc}
{$mode delphi}
{$endif}
procedure X(x1,x2:longint);stdcall;cdecl;pascal;
 begin
 end;

begin
 X(1,2);
end.

FPC 1.1 gives an error message:
test.pp(4,42) Error: Procedure directive "PASCAL" has conflicts with other directives
test.pp(4,42) Fatal: Syntax error, "BEGIN" expected but "identifier PASCAL" found

Delphi 3 compiles this sample successfully, I assume that last calling
convention directive overlaps all previous.
I think, Delphi behavior must at least be supported in $delphi mode of
FPC. Additionally, I think, procedure directives must be sorted into
groups to simplify and improve solving conflicts and overlapping.
I suggest:
1) introduce new type tProcDirKind=(pdk_Mangling, pdk_CallConv... etc;
2) add to proc_dir_rec type (unit pdecsub.pas) a new field, kind:
tProcDirKind;
3) differently check conflicts between directives for every kind;
4) separate handling of calling conventions from handling of name
mangling. This solution can seem to be painful, because can disturb
compatibility with older FPC versions, but I think, it is necessary.
New keywords like "cmangled", "cppmangled" etc must be introduced,
default using of calling conventions-related directives must cause no
changes in names mangling. Btw, relationships between name mangling and
calling conventions is not only strange but also somewhere wrong now. For
example, function TheFunc(x1:pchar;x2:longint):longint;stdcall;
now will be mangled in FPC to _THEFUNC$PCHAR$LONGINT but C/C++
compilers will mangle this stdcall function to _TheFunc at 8 .
That's not logical, to emulate C/C++ name mangling only for a part of common
calling conventions!

Another problem which is caused with the unasked name mangling
changes: A small demo which includes 2 units and one program which
used these units:

unit unit1;
interface
procedure test(x:longint);cdecl;
implementation
procedure test(x:longint);cdecl;
 begin
  writeln('1:',x);
 end;
end.

unit unit2;
interface
procedure test(x:longint);cdecl;
implementation
procedure test(x:longint);cdecl;
 begin
  writeln('2:',x);
 end;
end.

program main;
uses
 unit1,unit2;
begin
 unit1.test(100);
 unit2.test(100);
end.

Try to build this project without changes in sources!
I got problems at linking stage because both cdecl procedures in
different units have the same mangled name! This example demonstrates
that non-FPC name mangling must be used very carefully, but now it is
applying in very common cases. Btw, IMHO, even if the "automatic"
C-like name mangling would be excluded from FPC, the compiler became
not very less flexible because there are exist also syntax constructions
like
procedure TheProc(x1:pchar);stdcall;external name '_TheProc at 4';
for import and
procedure TheProc(x1:pchar);stdcall;[public,alias:'_TheProc at 4'];
for export.

I could also try to solve some these problems but I could know the
lot of my $calling patch, because solving ways depend on it.


-- 
Best regards,
 Pavel                          mailto:pavel at insect.ief.spb.su