Known bugs and inconveniences; how to report bugs

The GNU Pascal Compiler (GPC) does not yet implement the whole ISO 10206 Extended Pascal standard, not even the whole ISO 7185 Pascal standard. It is only partially compatible to Borland Pascal and implements only some isolated features from the PXSC standard. Furthermore, there are some known bugs which will take a long time to be fixed. (Any help welcome!) Please take this into account when you consider using GPC for any purpose.

If you encounter a bug with GPC, please check whether it is one of the known bugs. If not, report it to the GNU Pascal mailing list gpc@hut.fi. (But always report it if you solve the problem! ;-)

General bugs

• High optimization levels do not work properly on the Alpha. Some conformance tests fail when compiled with `-O6' flag, which means that the compiler generates invalid code. Don't use this flag in the Alpha before the problem gets fixed. It might have something to do with automatic inlining, but I have not yet looked at this. `-O' flag should be ok. (Also take care when using explicit inline functions.)
• Run time errors are not checked in most cases.
• For some reason the Pascal main program does not get lineno stabs, so it is hard to debug it with `gdb' ...
• The set code generated in the Alpha causes runtime errors in the generated code.
• There are some bugs with mathematical functions. GPC fails, for example, the "Paranoia" test.

Standard Pascal

• Type checking is mostly what C does, not what Pascal requires, so GPC does not yet implement a strongly typed language. Although correct programs compile, incorrect ones compile also. Please send us such incorrect programs, so we can fix it!

Extended Pascal

• Initialized structured variables are not yet implemented.
• Illegal substrings let crash the program rather than triggering a runtime error:

    str:='1234567890';
    i:=8; j:=13;
    str:=str[i..j];
  

  This is one case where runtime errors should be caught, but are not.

Borland Pascal

See also: section From Borland Pascal to GNU PascalQuickStart Guide for Borland Pascal users.

• Strings are implemented in a completely different way. They are not limited to 255 characters with the length being in position zero, but they are "Schema types" which is something more complicated.
• Most of Borland Pascal's System Unit is not implemented, e.g. `move', `FillChar', `BlockRead', `BlockWrite', `Assign', String-related functions, ... Workaround: Some of the missing procedures and functions are implemented in a separate compatibility Unit. Check the contrib subdirectory of your GPC distribution.
• The inline assember does not understand Borland syntax.
• There is no `private' directive for Objects yet.
• There is no `Inline' in Borland sense.

GNU Extensions

• The Run Time System (RTS) does not know about modified types such as `__byte__' or `__unsigned__ Integer's or `__long__ Real's. Especially, you cannot `writeln' such variables. Workaround: Cast them to their basis type before `writeln', e.g.

    Type
      Extended = __long__ Real;
  
    Var
      foo: Extended;
  
    [...]
  
    writeln ( Real ( foo ) );
  

Inconveniences

• The GNU debugger, `gdb', does not yet understand Pascal sets, files or subranges. Now `gdb' allows you to debug these things, even though it does not yet understand some stabs.
• Files of integer subranges that would fit in a byte do not; instead they are handled as files of integer. This is especially annoying with `file of 0..255'.

Notes for debugging

• Forward referencing pointers generate `dbx' style debugging symbols by outputting the `.stabs' as an unknown pointer and later it just outputs the same `.stabs' again, but this time it also tells what type the pointer points to. This seems to work for `gdb'. As of this writing I have not checked what happens with `sdb' type debugging info. It might be that the pointer is left to be a (void *) pointer, so you have to cast it in order to output the object the pointer points to. Also, we have not tried any other debugger than `gdb'. If you do, please let us know what happens. I think that GDB does not yet support the kind of `.stabs' that should be used to do this correctly:

    .stabs ":tanumber=bnumber", whatever
  

  where anumber is the unknown pointer type referenced earlier, and the bnumber is the type which anumber actually is. This construct is not required in C.
• When debugging, please note that the Initial Letter In Each Identifier Is In Upper Case And The Rest Are In Lower Case. If you wish to call C-routines declare them with the "C" directive, as follows:

  Procedure FooBAR(i:integer);c;
  

  This makes the external name to be `_foobar' (replace _ with you machine prefix).

  Procedure FooBAR(i:Integer); External;
  

  Uses external name _Foobar.

  Procedure FooBAR(i:Integer); AsmName 'FooBAR';
  

  Uses external name _FooBAR. It is done like this to reduce name clashes with `libc.a' and other possible libraries.
• All visible GPC runtime system library routines are named _p_....
• The main program name is preceeded by program_. For example, Program FOO yields the external name program_Foo for the main program. This is done because ISO Standard wants to have the program name in a separate name space.