From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793712706; b=BOp1R28X2G2YYYqtnypVUi8kE42Q8uEjejVOSoGcC/PoEgiLLAbSPmE6ITg49aMlyEq0 hyPiX7SgoojS6kDgOUb7QBkjEP34fWMyq3ldGwrno1n03RYz7/Gxr84R1ALuriwOih0ne AVdDKkOCjzQ/eYmP/fV2+PIZcE3xXPGUMCQE9mojAG4wtg24k7lArb5oQxDI9Y8g7Pgds iqX7h4+wkWwxvYFRMrfTdAKDXfY3a9DDTQ5elFgfloozyXbHJvdr5tPuaJ7r6xHMpPXb9 7M8qauh7WnAGpjzuvaHfFzI1x00p5w/3Wzt77dLWj/eUfeAHRGm1FZFErJCPfKWzPHw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793712706; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=62xUaQoKaHy86ervGNtnM45ld1Sm4ShPu6+Zz39RH44=; b=wKjxfjmi+supYORWuizURp1UXi4eQgRfvVbUHoCy/LLwZalFNpjNGQR+xyvqPROiJ1Zt FdDA4FdUzmTzFZbEQov3yFbCmz0LTi5WAYHu7N0gd/nopxCL/s/hD0eeeCiqK0JDCmkN4 SLte3xrkc20MGthrXNzzU0GoDZ0P2n8HPw7xiBknBSuVwn98NYI+AFR7hyW3RmapauqaX t9Zr1Ym2tQ+rOf7FT1Bt4CHUWNdHpl8ympkW0xosTt4mgneT08FVKi7wunMJ50ywzWgN5 dlrBt8jsdJZjPc0VHAdjvqqknGJp1Rf81F4IoD/JrsmhG+mA+AuMBy05ot6UFbVPnyQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=XQJYktRm; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4C878606A33D for ; Tue, 3 Nov 2026 13:31:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=XQJYktRm Received: by smtp.kernel.org (Postfix) with ESMTPSA id 11EEC1F0093A; Tue, 3 Nov 2026 13:31:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793712705; bh=62xUaQoKaHy86ervGNtnM45ld1Sm4ShPu6+Zz39RH44=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=XQJYktRmw/3EjBEv/79ns5vwpN9CQXGLoLCHNi0BkSW/tDCd0CPyZYSjr9pkAco/z KS9ObOtQBLn1JEbH8+k9K5oDuY+fLAvXf6kfJ+2PKATC2pYK7MCKQzhYQFj1aay1QV n99XniGdSyQJY52LNpSD/qqIOQYr/D4bVTK1pkza14DyTZ6Mv8S6QU9eTCKic3Nk4y KrJZzlmXEL1e+L7ZPbCB6GjXUD2qb0nZZogV9IOMnVcZFIn8BdY4HSChkFLq8ltzJr pxUkRBRi1BShniTfyqalKz2BQIuub9OrFZj39WSbVAwvQ9YIlN9wZjgLN8QUgGFNat IrZgARZy5uNdQ== Date: Tue, 3 Nov 2026 14:31:43 +0100 From: Alejandro Colomar To: Kees Cook , linux-hardening@vger.kernel.org Cc: Andy Shevchenko Subject: Re: [PATCH v1 1/2] args: Add DEFARG() to implement macro default arguments Message-ID: References: X-Mailing-List: linux-hardening@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="wab5bqux2z6owonk" Content-Disposition: inline In-Reply-To: --wab5bqux2z6owonk Content-Type: text/plain; protected-headers=v1; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable From: Alejandro Colomar To: Kees Cook , linux-hardening@vger.kernel.org Cc: Andy Shevchenko Subject: Re: [PATCH v1 1/2] args: Add DEFARG() to implement macro default arguments Message-ID: References: MIME-Version: 1.0 In-Reply-To: > Date: 2026-11-03 14:27:11+0100 > From: Alejandro Colomar > > It needs __VA_OPT__, which is a C23 feature, but it's provided by GCC > and Clang in GNU-C mode as an extension even without C23. __VA_OPT__ > was implemented in GCC 9 and Clang 6, I think, so it should be widely Actually, it seems it was implemented in Clang 12, not Clang 6. I got that 6 from llvmorg-6.0.0-rc1, but that version number seems to not be the same as the Clang version number. Anyway, Clang 12 should be fine, I think. Cheers, Alex > available. >=20 > Here's a small example program showing how this works: >=20 > alx@devuan:~/tmp$ cat d.c > #define D__(x, ...) (x) > #define D_(x, ...) D__(__VA_ARGS__ __VA_OPT__(,) x) > #define D(a, b) D_(a, b) > D(1, 2) > D(1, ) > D(, 2) > D(,) > alx@devuan:~/tmp$ gcc -E -Wall -Wextra d.c | grep '^[^#]' > (2) > (1) > (2) > () >=20 > Signed-off-by: Alejandro Colomar > --- > include/linux/args.h | 5 +++++ > 1 file changed, 5 insertions(+) >=20 > diff --git a/include/linux/args.h b/include/linux/args.h > index 0562dc51435e..5886011cf791 100644 > --- a/include/linux/args.h > +++ b/include/linux/args.h > @@ -3,6 +3,11 @@ > #ifndef _LINUX_ARGS_H > #define _LINUX_ARGS_H > =20 > +/* Expand to 'arg' if non-empty, or to 'def' if 'arg' is empty. */ > +#define ___DEFARG(x, ...) (x) > +#define __DEFARG(def, ...) ___DEFARG(__VA_ARGS__ __VA_OPT__(,) def) > +#define DEFARG(def, arg) __DEFARG(def, arg) > + > /* > * How do these macros work? > * > --=20 > 2.55.0 >=20 --=20 --wab5bqux2z6owonk Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAABCgAdFiEES7Jt9u9GbmlWADAi64mZXMKQwqkFAmrp4j4ACgkQ64mZXMKQ wqkJvw/9Ft00pDmyDeKPpFAeObGeHXW5QT+U6uISbK4K4LpxYzzEizvVCpyXO3AN WqpXsgZvX4iElSn2ssNph19XfLo+IBjiIuFoRD2BlMzImWibzmeyudkq3R8Xtxnv PdZKbn7REoGGY0pX194lI/Vhl4JmH4vgB9vhkXbmB35uBuKBABG8708CI1LmvkiU jyEJAGSA5JHGc6tYegRep/uqqh4DsZlfcUIXbV4Hfv4LYDYOaV4bv1lsKM90zfF0 i/+296Zy/dDyLilkHRMXy0kbdiUJ8600HmDlve7LD16PIRc9l+GJAohzwJrEhweB 2taUGEGqnssygos8oE9nLia0Xh7O+Vp7A+Z/U1B26b2CorQ8ThZn4/YBjTTxj5U0 xpGdOQBRw18lF+Ms48jqh6OnehfeCUxs1EYLAhYRQI/521PUm3dub4/NgPGfzPtH ZSVXN3QavxWLKOok9Jk3eeUPKegs3IyU25Cr7Q0PO8KWsBXbRdNKkwNWbodXunUz pWeLN1GBW8ShgSyBdGBFMjfoQmJ/FcjAQ4Q2zOI0ZsNsumAroUhmn4HCR4TmoXTy ltPeZVd9/feEJ42TFfAUFZmIJZHKYRajOJV5FvSTl3lWgXb+BzbdCFHJysNR8JDQ GsdybyHED5FxhFRoq9oyxxVFwFi+D03j4f/zYOZCuPhyKfxUvT0= =EZqH -----END PGP SIGNATURE----- --wab5bqux2z6owonk--