Re: forced casts question

Chris Pickett wrote:
> -    _svmt_stack_frame *frame = (_svmt_stack_frame *)
> +    _svmt_stack_frame *frame = (_svmt_stack_frame *) (void *)
>        (((char *) env->stack.current_frame) + offset);
> 
> I think this was to "eliminate tons of spurious warnings" (r3144), but 
> why were such things causing warnings?  Isn't it good to let the 
> compiler help you catch casting errors?

The casting error was about possible mi-alignment of the pointer, after 
casting.  In this case, as SableVM's stack frame computations are always 
done such as to guarantee correct alignment, the warning was spurious. 
Such spurious warnings, when issued in great quantity, can hide real 
warnings.  This is why I got rid of them using the ugly (and only) trick 
that allowed enabling GCC's cast warnings without being riddled with 
tons of spurious warnings.  I did check every single cast before adding 
"(void *)", to make sure I was not actually hiding a real problem.

Please note that for any new code, in general, it is *NOT* an accepted 
practice to write type casts directly in SableVM.  One should instead 
add an entry in cast.list and use the generated _svmf_cast_XXX() 
function to do a cast.

[I wonder if it would not be a good idea to even create special cast 
functions for computing the frame, local and stack pointers, and this 
centralize these dangerous hacks, while adding some additional type safety.]

Etienne

-- 
Etienne M. Gagnon, Ph.D.            http://www.info2.uqam.ca/~egagnon/
SableVM:                                       http://www.sablevm.org/
SableCC:                                       http://www.sablecc.org/

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