From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=209.85.128.47 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794392739; b=O6e76S7v9+bGs6vfUzYIpV0gIU6QaRoBA13HFaoOv3rIURoCLsavfV22VpEDAhwkgqUs KT8QkVRm9y9daYRW2L8PfsXz4e3cSu3wTmKDOu0sq6yXALn8/EdyFNooW6+MHvnhp6dtn U5a81bSuJ4zsgNa26qznsvnIa4cjLyYJUhu7a6Ub8727wmE9beYtNl0mDKvFVgWgvbQ7O HDM6kCVAPmnGu0EaYTWxkc7UkcvzJsk4K8p9mb3e9NQaY1R2MW+7B07mqcsaG1tw82AYu JALhFVkNldwWI6g3gwbBT4PKPrWZPGor4RgOdinUdj6pu/zIV/lQWBQZUWfVHfhzhTQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794392739; h=DMARC-Filter:Received:DKIM-Signature:X-Google-DKIM-Signature: X-Forwarded-Encrypted:X-Gm-Message-State:X-Gm-Gg:X-Received:Received: Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References:X-Mailer: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=WCGh2v7nU1b/qpgNrVkksi8LEcAJjTlz9SScJQHog1U=; b=p9NFA6eD3bgLsAi9/M79sKrCrdpGKdN5Pf3gb9q1klBBXcfjMZeem+l+jJXINb77/1xR xeuEhb9nsvKw5/1okvsL7h0z+0FHqURYiPPTADPmHrJoBkWIRQZv1UaO3ntf7db3W3T6O Wsj5WfqZYhV81v8qI0dbf9q/VHIo+fGUCxQCOvVgMEbol0Q1KUbXn+qGthaYTPLHMR3D0 5H1monWDDi43VCB2XfQjhq8KjEJMkxiPsuBr+sRn4JLIe+a6Ar09En6OzPfWiE71sYxw0 lGFP43vN3OZ5cGuPLrerf/QW6gB2oq0evD0Ry3IX9tmP5eQHjxYJlBoMv/wYkkQoVTA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=Mb3uhiUC; arc=none smtp.remote-ip=209.85.128.47 Received: from mail-wm1-f47.google.com (mail-wm1-f47.google.com [209.85.128.47]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 747D0606A32A for ; Wed, 11 Nov 2026 10:25:39 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org 747D0606A32A Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=Mb3uhiUC Received: by mail-wm1-f47.google.com with SMTP id 5b1f17b1804b1-4b467581b98so27573715e9.0 for ; Wed, 11 Nov 2026 02:25:39 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20260707; t=1794392738; x=1794997538; darn=vger.kernel.org; h=content-transfer-encoding:content-type:mime-version:references :in-reply-to:message-id:subject:cc:to:from:date:from:to:cc:subject :date:message-id:reply-to:content-type; bh=WCGh2v7nU1b/qpgNrVkksi8LEcAJjTlz9SScJQHog1U=; b=Mb3uhiUCOo+9OL8nkk0DPqlbHMU+U3YfPJtQRGohaqBLQ8OevIfv8dsETu4ueSqwRn NFUTwQnpCyUxKUDcsxzqJiYueO55nV4pkpQgYg9LUK5WPus9n/ERdDgHae8RQ7j2Dw+4 fM3ibr2Y6ts1e/OTqbgJiTQW3L8WDSaeJuxScEHyWMzPN+bGBiq2tlQqZ+g6LQEpKD58 mnmah5jGdWJ/FHCGptkaUokAM2nmjVjDMlQqXY1Y0+QNVEBolaI9RZeQ+wAs3afJIVDJ 0j7wdyVZa4FS6RKopL2kvM92RArS1Tu/5W/MXYkBtd4iocmh7ndrHYxmSyr8Mi6yyFzr +H+g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1794392738; x=1794997538; h=content-transfer-encoding:content-type:mime-version:references :in-reply-to:message-id:subject:cc:to:from:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=WCGh2v7nU1b/qpgNrVkksi8LEcAJjTlz9SScJQHog1U=; b=CWEONjtZjqJhmJsJr+kTPKBK3B0vVNGD+6HhjG12HB1/zDbuS2OKIL10YUg98paeUH iJuNg3DtOwvibv6CWiUtkS5nwqej8lMw7+AhaiU7tfYbnvXISAJ65k1/rafFpuBf3BB7 WZgn19+EeQRmyMLK1xXW+czyzb3SuwQjOraAfWGLwA+s5CFz7/mY/c5+YX1TqFWq35FG Mry/XRhpjcp1wq98iazNclwPHsvn87yQxf894CRapSg4+odvwVnYi2fTbCcdaD6eSIpR Z09jGzx/0fnW5V0oEYx5mK1OHbWdov+Q2GM2NICiieIZOwR75YS7aad2MIPRj8c9i3Qn 5YLg== X-Forwarded-Encrypted: i=1; AL+hErFXXccIV9u55IaFX6hF0MLqj3gz4J6dj1H92XxMHVD58IcKMmFj7a06GhhG2/J0jmuV3RTk3ePG0sJb@vger.kernel.org X-Gm-Message-State: APuU4Z8KDHsXfWER/n6h7xLg1m39BuV5rT9igkUDn5VAiPy2edYcvp+u Newu3StOjjXulCzCCE/5Z2fNM6PpAsbe14bXq9D0v/o01EXn7reSqIg+ X-Gm-Gg: AYBFou2UR9xOjm+KM9u6ISOp4MGXGW1OZDJf6SD16U7QieYnuqXDMZEKgccinRIHS4F qXTm765JFOnTVSUKMw4a+Tt2McVpW0gC6Tb6OMAnVzsNkJaKeDY3HKM4QPlZAJ7iQEL7y4+YvSy R3RaeGQoi6XCRs6bDEymqUMJgfVUwWX5VRHoJOJlguafpnQSSDfRf+XixQ6oZkK7qLuZQ/f27pP tGb/Y5MtBFLEfSBIVpOktBAuEf09ud8rQ1bKE9UlTKtPHNg/01+8bFgF3HYUnUccBwH5/Jet/Mw O3KDVg7qgeP+PwC4vxItYOWEOdroVOtLpe8uBLjOVALkFC8oLSESXFw6NEAaxvO4tuqn4kDS2fE slRta92Rabh9weRvgEEfALY/qRt0imp/ViIYWd9IsbPBqO+Bb2lU39ORCdP7MsAjBCbzhJ76/w5 rRjwKt2cJUTOd/KMzCDAFDp6zvZygWACBBs8pCa4L1SMYL75Bo7ChvOktT+6o0q2l3JYEJspnuU D3Zv7/mZAIYis5G1bLrn0TX/kabYLN2DxUzuKaS30XvlFv2ootdAIQPRNTLUSPr7jpQMNSRDIhh EaNtEJBv5qWozu6Ktq62W9esynQn2c8SaBKpai6Dj9LopgkWvS/wUuXda88eqtWwcFU= X-Received: by 2002:a05:600c:4f14:b0:4a6:44b:2593 with SMTP id 5b1f17b1804b1-4ba093b5ec4mr41235955e9.29.1794392737707; Wed, 11 Nov 2026 02:25:37 -0800 (PST) Received: from pumpkin (82-69-66-36.dsl.in-addr.zen.co.uk. [82.69.66.36]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4988f5b1ce3sm8610917f8f.14.2026.11.11.02.25.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 Nov 2026 02:25:37 -0800 (PST) Date: Wed, 11 Nov 2026 10:25:35 +0000 From: David Laight To: Alejandro Colomar Cc: linux-hardening@vger.kernel.org, Krzysztof Kozlowski , "Maciej W. Rozycki" , Geert Uytterhoeven , Andreas Schwab , Andy Shevchenko , Bartosz Golaszewski , Daniel Scally , Danilo Krummrich , Greg Kroah-Hartman , Hans Verkuil , Heikki Krogerus , Joe Perches , Johan Hovold , Kees Cook , Laurent Pinchart , Len Brown , Linus Torvalds , Linus Walleij , Namhyung Kim , "Rafael J. Wysocki" , Rob Herring , Sakari Ailus , Saravana Kannan , Steven Rostedt , Tom Zanussi , linux-acpi@vger.kernel.org, driver-core@lists.linux.dev, linux-kernel@vger.kernel.org, devicetree@vger.kernel.org, linux-gpio@vger.kernel.org Subject: Re: [PATCH v3 3/5] stddef: Add const_cast() Message-ID: <20261111102535.434c2eee@pumpkin> In-Reply-To: <2bf5cf7baad87b5b7b7f833df390596a033fd6f6.1794323750.git.alx@kernel.org> References: <2bf5cf7baad87b5b7b7f833df390596a033fd6f6.1794323750.git.alx@kernel.org> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) X-Mailing-List: devicetree@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Tue, 10 Nov 2026 16:33:40 +0100 Alejandro Colomar wrote: > This macro serves to cast const away without risking unwanted > conversions due to mistakes in the cast. > > It's similar to C++'s const_cast(), but it is more restrictive: it can > only cast away 'const', and not arbitrary qualifiers. > > Signed-off-by: Alejandro Colomar > --- > include/linux/stddef.h | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/include/linux/stddef.h b/include/linux/stddef.h > index e1851c50c89b..d79a81406b78 100644 > --- a/include/linux/stddef.h > +++ b/include/linux/stddef.h > @@ -194,4 +194,16 @@ enum { > #define TRAILING_OVERLAP(TYPE, NAME, FAM, MEMBERS) \ > __TRAILING_OVERLAP(TYPE, NAME, FAM, /* no attrs */, MEMBERS) > > +/** > + * const_cast() - Drop const in the left-most derivation of a pointer > + * > + * @T: Type for the cast. > + * @p: Pointer to be casted. > + * > + * If @p is of type const @T, then it is casted to @T. > + * Otherwise, @p is returned without any casts. > + * This avoids mistakes that change anything other than 'const' in a cast. > + */ > +#define const_cast(T, p) _Generic(p, const T: (T) (p), default: (p)) Should it be de_const_cast(), or just de_const(). It is a shame you need to specify the type, but why not: _Generic(p, T: p, const T: (T)(p)) so that you get a compile time error from the _Generic() if the type is wrong. David > + > #endif