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

Pierre Muller
2003-02-18T08:17:29Z

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?