linux-kernel - Re: include/net/sock.h:2100:16: sparse: sparse: cast to non-scalar

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Message-ID: <20260112192126.GJ3634291@ZenIV>
Date: Mon, 12 Jan 2026 19:21:26 +0000
From: Al Viro <viro@...iv.linux.org.uk>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
	Eric Dumazet <edumazet@...gle.com>, oe-kbuild-all@...ts.linux.dev,
	linux-kernel@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
	Maciej Żenczykowski <maze@...gle.com>,
	Will Deacon <will@...nel.org>,
	"Paul E. McKenney" <paulmck@...nel.org>
Subject: Re: include/net/sock.h:2100:16: sparse: sparse: cast to non-scalar

On Mon, Jan 12, 2026 at 01:37:22PM +0100, Peter Zijlstra wrote:

> > #define unqual_non_array(T) __typeof__(((T(*)(void))0)())
> > 
> > would do the right thing without that _Generic cascade and it'll work
> > just fine for e.g. kuid_t.  Using it for an array would trigger an error,
> > array-returning functions being forbidden...
> > 
> > Guys, do you have any problems with replacing __unqual_scalar_typeof()
> > uses with that thing?
> 
> There is also __typeof_unqual__, but I do not know if that is now
> supported by all compilers, if so that is the better option. If not,
> your function return type thing is awesome.

>From experimenting with godbolt.org:
			clang		gcc		icc
__typeof_unqual__	>= 19.0.1	>= 14.1		no
this trick		>= 3.0.0	>= 8.4		>= 13.0.1
our minima		15.0.0		8.1

So __typeof_unqual__ is well out of our range; this trick is slightly
out of range, but nowhere near as bad.  Prior to 8.4 gcc had a bug
in that area, unfortunately ;-/

Might make sense to reconsider it next time we bump gcc minimum...