Andrew Haley wrote: > Yuri Pudgorodsky writes: > > > > > We can say something like: > > > > > > "In GNU C, you may cast a function pointer of one type to a function > > > pointer of another type. If you use a function pointer to call a > > > function, and the dynamic type of the function pointed to by the > > > function pointer is not the same as indicated by the static type of the > > > function pointer, then the results of the call are unspecified. In > > > general, if the types are not too different > > s/not too different/compatible/ > > "not too different" has no meaning, whereas "compatible" is defined in > Section 6.2.7.
But, at least in C++, the official meaning of compatible is not the meaning we want. For example, "int *" and "long *" are not compatible -- but, in this context, we want to say that this will work. > We need to do this because we use type-based alias analysis in gcc. Yes, I remember adding that feature. :-) :-) > If we permit incompatible > types to be casted in function calls, we make a hole in alias > analysis. Yes, users who lie will lose. The only thing we're trying to do here is behave a bit more gracefully. Introducing a call to __builtin_trap is pretty brutal; instead, we want to say "we can't promise this is going to work, but if you want to try, go ahead..." -- Mark Mitchell CodeSourcery [EMAIL PROTECTED] (650) 331-3385 x713
