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
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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
