Re: c/4101: gcc 2.95.4 compiles bad code with nested static functions

[Bernd Schmidt <bernds at redhat dot com>]

(I currently can't access the gnatsweb page for some reason, otherwise
I'd have closed this.  If gnats works for someone, please close...).

> /* this must do a certain thing only the 1st time,
>    but we don't want a check as if (first_time) {do},
>    so we use a function pointer that the first time
>    does, the others just returns.
>  */
> void loop(void)
> {
>    void f1(void);
>    void f2(void);
>    static void (*f)(void) = f1;
>
>    void f2(void) { } /* this is empty */
>
>    void f1(void)
>    {
>       /* ... do something */
>       f=f2; /* the problem is HERE */
>    }
>
>    (*f)(); /* do something only the first time */
> }

This isn't actually valid.  The line

>    static void (*f)(void) = f1;

constructs a trampoline on the current stack of the function loop, and
once you've exited from that function, the contents of the stack are
no longer valid.  Basically, f1 is treated as a local variable, and you
can't keep pointers to those across multiple calls to a function either.


Bernd