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Date: Tue, 1 Oct 2002 16:56:59 -0700
From: Burton Samograd <kruhft@kruhft.dyndns.org>
To: Lista Linux-Kernel <linux-kernel@vger.kernel.org>
Subject: Re: bad function ptrs - is it dangerous ?
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On Wed, Oct 02, 2002 at 12:51:25AM +0200, J.A. Magallon wrote:
> I have a little question. Let's suppose you have this:
>=20
> int (*pf)(data *);
> int f(data*);
>=20
> so you can:
>=20
> pf =3D f;
> pf(data).
>=20
> Fine. But what happens if:
>=20
> void (*pf)(data *);
> int f(data*);
>=20
> pf =3D f; // gcc happily swallows, gcc-3.2 gives a warning.
> pf(data).
>=20
> ??
>=20
> In C calling convention, the callee kills the stack so nothing should
> happen... or it should ?
>

I think that under most calling conventions return values are put into
registers, so this shouldn't do anything other than keep the compiler from
reallocating the designated return register for a while.

Or, after a second or two of more thought, it might cause the function to t=
rash
whatever value is contained in the return register, which the compiler thou=
ght
was safe from harm.  It all depends on the calling convention and whether t=
he
caller assumes that the callee can destroy any registers or if the callee h=
as to
save and restore the registers it uses.

burton

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