RE: [PATCH v2] hwmon: (dell-smm) Improve assembly code

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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)




[Index of Archives]     [Kernel Newbies]     [Security]     [Linux C Programming]     [Linux for Hams]     [DCCP]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux RAID]     [Linux Admin]     [Samba]     [Video 4 Linux]

  Powered by Linux