Re: Attention ROOT users: bug in GCC

jarek Grebieszkow (Jarek.Grebieszkow@cern.ch)
Mon, 20 Oct 1997 18:29:16 +0200 (METDST)

I think it is a problem with virtual function table generation. I
solved this problem by puting class definition and implementation in
separate files and adding in defnition file #pragma interface and in
implementation file #pragma implementation . Second solution I think is to
add (if we keep definition and implementation it the same file)
implementation of that virtual function.

Jarek

On Mon, 20 Oct 1997, Pasha Murat wrote:

>
> Those of us who use GCC-compiled ROOT shold be aware of a weird
> compiler bug present in version 2.7.2.x:
>
> declaration of virtual function in the class header makes compiler
> (sometimes?) to forget about the definitions of inline methods of this
> class:
> ---------------------------------------------------------- test.cc
> class A {
> int a;
> public:
> A();
> ~A();
> inline int aa() { return 1; }
> virtual int qqqq();
> };
>
> main() {
> A q;
> int b = q.aa();
> }
> --------------------------------------------------
> /data35/upgrade/murat/run1>gcc -c test.cc ; nm test.o | grep aa
> U aa__1A
> --------------------------------------------------------------------------------
> You see that *inline* method A::aa() body of which should normally be inserted
> into the source code has been considered to be an *external* function by GCC.
>
> As ClassDef(..) macro contains declarations of virtual functions this may cause
> problems for people using GCC-compiled ROOT.
>
> This "feature" is reproducible on IRIX 6.2 and on AIX 4.2.
> For some reasons switching ON optimization on AIX resolves the problem, on
> IRIX however it doesn't help. I didn't try versions of GCC other than
> 2.7.2.1(IRIX) and 2.7.2.2(AIX Power PC).
>
> The only other C++ compiler I tried on UNIX - KAI C++ (on IRIX 6.2) doesn't
> have this bug.
> Regards, Pasha.
>