From xen-devel  Thu May 05 20:08:55 2022
From: Keith Packard <keithp () keithp ! com>
Date: Thu, 05 May 2022 20:08:55 +0000
To: xen-devel
Subject: Re: [PATCH 02/32] Introduce flexible array struct memcpy() helpers
Message-Id: <87pmkrpwrs.fsf () keithp ! com>
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Kees Cook <keescook@chromium.org> writes:

> I don't think I can do a declaration and an expression statement at the
> same time with different scopes, but that would be kind of cool. We did
> just move to c11 to gain the in-loop iterator declarations...

Yeah, you'd end up creating a statement-level macro, and I think that
would have poor syntax:

        mem_to_flex_dup(struct something *instance, rc, byte_array,
                        count, GFP_KERNEL);
        if (rc)
           return rc;

I bet you've already considered the simpler form:

        struct something *instance =3D mem_to_flex_dup(byte_array, count, G=
FP_KERNEL);
        if (IS_ERR(instance))
            return PTR_ERR(instance);

This doesn't allow you to require a new name, so you effectively lose
the check you're trying to insist upon.

Some way to ask the compiler 'is this reference dead?' would be nice --
it knows if a valid pointer was passed to free, or if a variable has not
been initialized, after all; we just need that exposed at the source
level.

=2D-=20
=2Dkeith

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