Re: [PATCH] scsi: Let scsi_execute_cmd() mark args->sshdr as invalid

[Martin Wilck]

On Thu, 2023-05-11 at 15:17 +0200, Juergen Gross wrote:
> > 
> > We know for certain that sizeof(*sshdr) is 8 bytes, and will most
> > probably remain so. Thus
> > 
> >      memset(sshdr, 0, sizeof(*sshdr))
> > 
> > would result in more efficient code.
> 
> I fail to see why zeroing a single byte would be less efficient than
> zeroing
> a possibly unaligned 8-byte area.

I don't think it can be unaligned. gcc seems to think the same. It
compiles the memset(sshdr, ...) in scsi_normalize_sense() into a single
instruction on x86_64.

0xffffffff8177e9d0 <scsi_normalize_sense>:      nopl   0x0(%rax,%rax,1) [FTRACE NOP]
0xffffffff8177e9d5 <scsi_normalize_sense+5>:    test   %rdi,%rdi
0xffffffff8177e9d8 <scsi_normalize_sense+8>:    movq   $0x0,(%rdx)

Martin