Stack checking in GNAT (was: ada compiler?)

[Ludovic Brenta <ludovic@ludovic-brenta.org>]

Samuel Tardieu writes:
> You have two ways of doing stack checking:
>
>  1- at the GCC level by checking the stack at the entry of every
>     subprogram and comparing it to a thread/task specific marker; this
>     is costly
>
>  2- at the OS level by mapping a page after the stack which does not
>     allow either reads or writes to the page (or, when this is not
>     possible, which doesn't allow writes)

[detailed explanation]

> Does that answer your question?

Yes, thank you very much.  It seems that I can enable or disable stack
checking, and select from the two methods above, by patching some
flags in System and Targparm.  In System:

   Stack_Check_Default       : constant Boolean := False;
   Stack_Check_Probes        : constant Boolean := False;

Stack_Check_Default is True only on VMS.

Stack_Check_Probes is True only on VMS, IRIX, MinGW, Solaris and Tru64
Unix (it depends on the OS, not the processor).

And in Targparm.ads:

   Stack_Check_Probes_On_Target : Boolean := False;
   --  Indicates if stack check probes are used, as opposed to the standard
   --  target independent comparison method.

(the "stack check probes" are method 2, the "standard target
independent comparison method" is method 1)

   Stack_Check_Default_On_Target : Boolean := False;
   --  Indicates if stack checking is on by default

I don't understand the difference between the flags in System and
those in Targparm (i.e. why are there two sets of flags, and what
happens if their values are different?).  Also I am curious to know
what would be the effect of changing these flags in Debian.  Can you
help?

-- 
Ludovic Brenta.