Messages in this thread | | | Subject | Re: [PATCH v2] hwmon: (dell-smm) Improve assembly code | From | Armin Wolf <> | Date | Sun, 20 Feb 2022 20:05:17 +0100 |
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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
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