From mboxrd@z Thu Jan 1 00:00:00 1970 From: Armin Wolf Subject: Re: [PATCH v2] hwmon: (dell-smm) Improve assembly code Date: Sun, 20 Feb 2022 20:05:17 +0100 Message-ID: <77eeca08-e970-84df-6490-36e330ce91ca@gmx.de> References: <20220219211011.16600-1-W_Armin@gmx.de> <6f4c21b5e1cb4fa38a5e0c1716658329@AcuMS.aculab.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gmx.net; s=badeba3b8450; t=1645383920; bh=6KNpyc0ZW7k54/xmz9GluUG6R/Rcoqer5CR8Xt+p03g=; h=X-UI-Sender-Class:Subject:To:Cc:References:From:Date:In-Reply-To; b=gcsDqFRvghF/nV5U7WrtjeBCt9E9BnAx7jpWah7N1dQJH7AhpruPDtVJEiZpJWaJ8 nV47flPc2mS6ZNYVMU7+ITwYbC0BFXPQqMcCP4kzsr1vEbu+4RN9s7M0j40vQ91l7Y joWLjbIRBk8swaJY0OQT6843u5vEOcutrhMxy6BM= In-Reply-To: <6f4c21b5e1cb4fa38a5e0c1716658329@AcuMS.aculab.com> Content-Language: en-US List-ID: Content-Type: text/plain; charset="us-ascii"; format="flowed" To: David Laight , "pali@kernel.org" Cc: "jdelvare@suse.com" , "linux@roeck-us.net" , "linux-hwmon@vger.kernel.org" , "linux-assembly@vger.kernel.org" , "linux-kernel@vger.kernel.org" Am 20.02.22 um 19:48 schrieb David Laight: > From: Armin Wolf >> Sent: 19 February 2022 21:10 >> >> The new assembly code works on both 32 bit and 64 bit >> cpus and allows for more compiler optimisations by not >> requiring smm_regs to be packed > I'm intrigued about the __packed.. > > Prior to 5.17-rc1 __packed was only applied to the fields after 'eax'. > This actually has no effect (on any architecture) because there is > no padding to remove - so all the later fields are still assumed to > be 32bit aligned. > > 5.17-rc1 (565210c781201) moved the __packed to the end of the > structure. > AFAICT this structure is only ever used in one file and for on-stack > items. It will always actually be aligned and is only read by the > code in the file - so why was it ever marked __packed at all! > On x86 it would make no difference anyway. > > I can only guess it was to ensure that the asm code didn't go > 'wrong' because of the compiler adding 'random' padding. > That isn't what __packed is for at all. > The linux kernel requires that the compiler doesn't add 'random' > padding - even if the C standard might allow it. > > David > > - > Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK > Registration No: 1397386 (Wales) > Your right, after looking at the assembly output, i can confirm that the removal of __packed changed nothing. Maybe i should update this part of the commit message as well. Armin Wolf