From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sender4-op-o12.zoho.com (sender4-op-o12.zoho.com [136.143.188.12]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 52CCA2F432A; Thu, 12 Jun 2025 12:12:57 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=pass smtp.client-ip=136.143.188.12 ARC-Seal:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749730380; cv=pass; b=i/5ktvIVLpKsKbXa2RSPONNdq+DHkqdiE/LLW6P19PwuT2KbK6PLOXKtrMwrLwX83EbS4UQat9tyAnN1Fh1AXYQ4xukvSSXv+kNM8l/73Tsevn4sdqP6T8cZB8DzOZmF74bET2vaVG2Q2IsUYd8DbQtji/EnmXOWPw5axyTO82o= ARC-Message-Signature:i=2; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1749730380; c=relaxed/simple; bh=+kdiXiiHozxtvIIE7QcPklTRBLEyuoJrKDGLNl7vclA=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=jhlVHwGs0atC6wFTydq3STswYSrQKfBnrM5VzawB5s4JJ02elAHbydRlrbz4fw+J29ItNU/3G9/hMGxV/EgmDh1LZdNURwnz/ssi/cCmlPpzhss89Mz/ritDJFU7cQFajHoj9NijkjcBS0w6Deg1UPD/8eaTWqQMQeioovuJen8= ARC-Authentication-Results:i=2; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com; spf=pass smtp.mailfrom=collabora.com; dkim=pass (1024-bit key) header.d=collabora.com header.i=nicolas.frattaroli@collabora.com header.b=SK7OXUzc; arc=pass smtp.client-ip=136.143.188.12 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=collabora.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=collabora.com header.i=nicolas.frattaroli@collabora.com header.b="SK7OXUzc" ARC-Seal: i=1; a=rsa-sha256; t=1749730279; cv=none; d=zohomail.com; s=zohoarc; b=gLVUSH8whkjznJ84HhEKxxnjU2XuDwX04WtVl7Ke0k/VtxuyHepvYyZFEsDsuRxdsOR+mZGQaf6prN0Jl3RFazK5tsm20vUPJNrfC7uMH7EkaAb8x+J6/uAl/jUVupirBlfKqcEg9lOnbR3b7+HuupT2MjpmNEg4RkgTVsrnDEU= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1749730279; h=Content-Type:Content-Transfer-Encoding:Cc:Cc:Date:Date:From:From:In-Reply-To:MIME-Version:Message-ID:References:Subject:Subject:To:To:Message-Id:Reply-To; bh=anKlnwbFl0i8atiPf5c4Ks2L7I/qYyoFEOqCpl8Xjz4=; b=NnYk+ho5QsNnUw/GyWrBWAlNSFdprVwt/SMpMEjygvo543BdEKRBHtfoDB0IlobqSRFj3aQKnfuW61HRwi3mlbyo7MjKlqvXIxcbmt1jg1nM3R/1ZxeziAGckm4SGc4esonsJ/LIuXqmUTX6AGNZ7pwSisvbKzWfbHfGMTWV5H8= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=pass header.i=collabora.com; spf=pass smtp.mailfrom=nicolas.frattaroli@collabora.com; dmarc=pass header.from= DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; t=1749730279; s=zohomail; d=collabora.com; i=nicolas.frattaroli@collabora.com; h=From:From:To:To:Cc:Cc:Subject:Subject:Date:Date:Message-ID:In-Reply-To:References:MIME-Version:Content-Transfer-Encoding:Content-Type:Message-Id:Reply-To; bh=anKlnwbFl0i8atiPf5c4Ks2L7I/qYyoFEOqCpl8Xjz4=; b=SK7OXUzcTO6J2OvgkAoNUrfYDQNfzeYE74UjS+nOX7vgUkpRNbgyTF8jQkg2hh0D dUAV/oN8qsLxpnK+Y+fEssRjHR7B+gVr7b2h2PGccmdr2X9JotCuSJJ08Fv1WSCt0fN YQykWtOBwsZmWFYSR+CE0ujPPquYI14ZwNERJFwc= Received: by mx.zohomail.com with SMTPS id 1749730276781981.6042234328434; Thu, 12 Jun 2025 05:11:16 -0700 (PDT) From: Nicolas Frattaroli To: David Lechner , linux-rockchip@lists.infradead.org Cc: Michael Hennerich , Lars-Peter Clausen , Jonathan Cameron , Nuno =?UTF-8?B?U8Oh?= , Andy Shevchenko , Matthias Brugger , AngeloGioacchino Del Regno , Heiko Stuebner , Maxime Coquelin , Alexandre Torgue , Francesco Dolcini , =?UTF-8?B?Sm/Do28gUGF1bG8gR29uw6dhbHZlcw==?= , Leonard =?UTF-8?B?R8O2aHJz?= , kernel@pengutronix.de, Oleksij Rempel , Roan van Dijk , Tomasz Duszynski , Jacopo Mondi , Jean-Baptiste Maneyrol , Mudit Sharma , Javier Carrasco , =?UTF-8?B?T25kxZllag==?= Jirman , Andreas Klinger , Petre Rodan , linux-iio@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mediatek@lists.infradead.org, linux-rockchip@lists.infradead.org, linux-stm32@st-md-mailman.stormreply.com, Pavel Machek Subject: Re: [PATCH 00/28] iio: zero init stack with { } instead of memset() Date: Thu, 12 Jun 2025 14:11:08 +0200 Message-ID: <2243943.irdbgypaU6@workhorse> In-Reply-To: References: <20250611-iio-zero-init-stack-with-instead-of-memset-v1-0-ebb2d0a24302@baylibre.com> Precedence: bulk X-Mailing-List: linux-iio@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" Hello, I thought I'd chime in as someone uninvolved because this seemed interesting. On Thursday, 12 June 2025 11:17:52 Central European Summer Time Pavel Machek wrote: > Hi! > > > Jonathan mentioned recently that he would like to get away from using > > memset() to zero-initialize stack memory in the IIO subsystem. And we > > have it on good authority that initializing a struct or array with = { } > > is the preferred way to do this in the kernel [1]. So here is a series > > to take care of that. > > 1) Is it worth the churn? > > 2) Will this fail to initialize padding with some obscure compiler? as of right now, the only two C compilers that are supported are GCC >= 8.1, and Clang >= 13.0.1. If anyone even manages to get the kernel to finish a build with something else, I think the compiler not implementing the C standard correctly is the least of their worries. My bigger worry is that = { } is only guaranteed to be as correct as memset on C23, and the kernel's standard right now is C11. For that reason alone, I don't think memset should be moved away from for now, unless someone can verify that every GCC release >= 8.1 and every Clang release >= 13.0.1 does the right thing here regardless. > > 3) Why do you believe that {} is the preffered way? All we have is > Kees' email that explains that = {} maybe works in configs he tested. = { } is guaranteed to work in C23, as per the standard, but again we're not on C23. The reason to prefer this is likely that it's easier for static analysis to see the struct as initialised, but that's me making assumptions here. A more human-centric argument is that once we're on a C standards version where = { } is guaranteed to be correct, then = { } is much more obviously correct to a reader than a memset with a value and a size somewhere later in the code. This argument is evident from the number of patches in this series where the memset and the declaration are not in the same hunk. That's the kind of stuff that keeps me awake at night, sweating profusely. Kind regards, Nicolas Frattaroli > > BR, > Pavel > > > [1]: > > https://lore.kernel.org/linux-iio/202505090942.48EBF01B@keescook/ > > > > > --- > > David Lechner (28): > > iio: accel: adxl372: use = { } instead of memset() > > iio: accel: msa311: use = { } instead of memset() > > iio: adc: dln2-adc: use = { } instead of memset() > > iio: adc: mt6360-adc: use = { } instead of memset() > > iio: adc: rockchip_saradc: use = { } instead of memset() > > iio: adc: rtq6056: use = { } instead of memset() > > iio: adc: stm32-adc: use = { } instead of memset() > > iio: adc: ti-ads1015: use = { } instead of memset() > > iio: adc: ti-ads1119: use = { } instead of memset() > > iio: adc: ti-lmp92064: use = { } instead of memset() > > iio: adc: ti-tsc2046: use = { } instead of memset() > > iio: chemical: scd4x: use = { } instead of memset() > > iio: chemical: scd30: use = { } instead of memset() > > iio: chemical: sunrise_co2: use = { } instead of memset() > > iio: dac: ad3552r: use = { } instead of memset() > > iio: imu: inv_icm42600: use = { } instead of memset() > > iio: imu: inv_mpu6050: use = { } instead of memset() > > iio: light: bh1745: use = { } instead of memset() > > iio: light: ltr501: use = { } instead of memset() > > iio: light: opt4060: use = { } instead of memset() > > iio: light: veml6030: use = { } instead of memset() > > iio: magnetometer: af8133j: use = { } instead of memset() > > iio: pressure: bmp280: use = { } instead of memset() > > iio: pressure: mpl3115: use = { } instead of memset() > > iio: pressure: mprls0025pa: use = { } instead of memset() > > iio: pressure: zpa2326: use = { } instead of memset() > > iio: proximity: irsd200: use = { } instead of memset() > > iio: temperature: tmp006: use = { } instead of memset() > > > > drivers/iio/accel/adxl372.c | 3 +-- > > drivers/iio/accel/msa311.c | 4 +--- > > drivers/iio/adc/dln2-adc.c | 4 +--- > > drivers/iio/adc/mt6360-adc.c | 3 +-- > > drivers/iio/adc/rockchip_saradc.c | 4 +--- > > drivers/iio/adc/rtq6056.c | 4 +--- > > drivers/iio/adc/stm32-adc.c | 3 +-- > > drivers/iio/adc/ti-ads1015.c | 4 +--- > > drivers/iio/adc/ti-ads1119.c | 4 +--- > > drivers/iio/adc/ti-lmp92064.c | 4 +--- > > drivers/iio/adc/ti-tsc2046.c | 3 +-- > > drivers/iio/chemical/scd30_core.c | 3 +-- > > drivers/iio/chemical/scd4x.c | 3 +-- > > drivers/iio/chemical/sunrise_co2.c | 6 ++---- > > drivers/iio/dac/ad3552r.c | 3 +-- > > drivers/iio/imu/inv_icm42600/inv_icm42600_accel.c | 5 ++--- > > drivers/iio/imu/inv_icm42600/inv_icm42600_gyro.c | 5 ++--- > > drivers/iio/imu/inv_mpu6050/inv_mpu_acpi.c | 4 +--- > > drivers/iio/imu/inv_mpu6050/inv_mpu_ring.c | 6 ++---- > > drivers/iio/light/bh1745.c | 4 +--- > > drivers/iio/light/ltr501.c | 4 +--- > > drivers/iio/light/opt4060.c | 4 +--- > > drivers/iio/light/veml6030.c | 4 +--- > > drivers/iio/magnetometer/af8133j.c | 4 +--- > > drivers/iio/pressure/bmp280-core.c | 5 +---- > > drivers/iio/pressure/mpl3115.c | 3 +-- > > drivers/iio/pressure/mprls0025pa_i2c.c | 5 +---- > > drivers/iio/pressure/zpa2326.c | 4 +--- > > drivers/iio/proximity/irsd200.c | 3 +-- > > drivers/iio/temperature/tmp006.c | 4 +--- > > 30 files changed, 34 insertions(+), 85 deletions(-) > > --- > > base-commit: 4c6073fec2fee4827fa0dd8a4ab4e6f7bbc05ee6 > > change-id: 20250611-iio-zero-init-stack-with-instead-of-memset-0d12d41a7ecb > > > > Best regards, > >