lkml.org 
[lkml]   [2023]   [May]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] scsi: Let scsi_execute_cmd() mark args->sshdr as invalid
From
Date
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

\
 
 \ /
  Last update: 2023-05-11 15:25    [W:0.490 / U:0.020 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site