Re: [RFC] New file fpc-abi.c

[Pierre Muller <muller at ics dot u-strasbg dot fr>]

At 18:31 17/02/2003, Daniel Jacobowitz wrote:
>On Mon, Feb 17, 2003 at 06:12:17PM +0100, Pierre Muller wrote:
>>   This patch adds a new file fpc-abi.c
>> to the gdb directory.
>> 
>>   The purpose of this file is rather clear:
>> it allows to recognize Free Pascal compiled 
>> objects and to handle ABI stuff in a more 
>> adequate way.
>> 
>> Should I submit this in several RFA?
>> 
>> 
>> ChangeLog entry:
>> 
>> 2003-02-17  Pierre Muller  <muller@ics.u-strasbg.fr>
>> 
>>         * fpc-abi.c: New file.
>>         Implements Free Pascal specific ABI.
>>         * minsyms.c (install_minimal_symbols): Recognize
>>         Free Pascal compiled objects by the presence of
>>         'fpc_compiled' minimal symbol.
>>         * Makefile.in: Add fpc-abi.c compilation rules.
>
>A lot of this file looks like it was just copied from one of the GNU
>C++ ABI files.  Certainly the comments are now wrong.  Is a lot of the
>code really appropriate?  i.e. does Free Pascal have the concept of an
>RTTI type, or virtual functions, or operator names?
>
>These are listed as C++ ABIs.  Adding one for Pascal feels dodgy.


Free Pascal does have most of these.

 - The pascal objects are a little bit different from 
the C++ classes, in the sense that they are basically 
struct that can (but do not always) have a
hidden field, that contains the address of a Virtual Method Table
i.e. a structure that contains information about
the virtual methods of the give object type.
- Free Pascal also knows Delphi like classes
which are more similar to C++ classes, in the sense
that they are just pointers to strucutures allocated on heap
in constructor calls.

- Run Time Type Information is also supported for 
Free Pascal classes, but I did not yet check this part of the code,
because I did never really use it until now.
My idea was that these parts can still be corrected after 
this file is in CVS.

 - operators are also supported in Free Pascal,
but the fpc_is_operator_name is not yet correctly implemented.

I should probably add explicit comments about the
state of the different funtions implemented in this file.


The fact that several functions are the same as in gnu-v2-abi.c
are due to the fact that, we I tried to add correct object/class 
debugging stabs generation, I tried to generate 
gnu-v2 compatible output.
This explains for instance that the is_(cons/des)tructor_name 
functions are the same.

fpc_is_vtable_name is completely Fre Pascal specific.
The other important point is that the recognition of 
Free Pascal compiled objects avoid to treat them as gnu-v3 
files, which can be the case with current head CVS GDB if they are linked together with
C files that use this ABI.
Indeed, the gnu-v3 code leads to crashes inside the GDB
code itself when trying to get class informations.

I do not claim that the fpc-abi.c is a completely correct code,
but:
  1) it avoids some internal GDB crashes when trying to debug executables
that contain both FPC and GNU C v3 generated code.
  2) It enhances the class recognition with respect to the gnu-v2
ABI.
  3) It is only used if the object has a fpc_compiled minimal symbol,
which should be enough to avoid any interference with other compiler, no?