svn commit: r295768 - head/usr.sbin/iostat

[Sergey Kandaurov]

On 18 February 2016 at 23:08, Alan Somers <asomers at freebsd.org> wrote:
> Author: asomers
> Date: Thu Feb 18 20:08:01 2016
> New Revision: 295768
> URL: https://svnweb.freebsd.org/changeset/base/295768
>
> Log:
>   Fix compiler warnings in iostat

> Modified: head/usr.sbin/iostat/iostat.c
> ==============================================================================
> --- head/usr.sbin/iostat/iostat.c       Thu Feb 18 19:37:39 2016        (r295767)
> +++ head/usr.sbin/iostat/iostat.c       Thu Feb 18 20:08:01 2016        (r295768)
> @@ -117,30 +117,34 @@
>  #include <termios.h>
>  #include <unistd.h>
>
> -struct nlist namelist[] = {
> +static struct nlist namelist[] = {
>  #define X_TTY_NIN      0
> -       { "_tty_nin" },
> +       { .n_name = "_tty_nin",
> +         .n_type = 0, .n_other = 0, .n_desc = 0, .n_value = 0 },
>  [...]

You unlikely need this excessive explicit zeroization.
In this case it is implicitly prezeroed.

Consider these two cases:

: #include <nlist.h>
:
: int main(void) {
:   struct nlist namelist[2] = {{ .n_type = 0x42 }};
:   return sizeof(namelist);
: }

(__TEXT,__text) section
_main:
0000000000000000    pushq    %rbp
0000000000000001    movq    %rsp, %rbp
0000000000000004    leaq    -0x30(%rbp), %rdx
0000000000000008    movl    $0x0, %eax
000000000000000d    movl    $0x6, %ecx
0000000000000012    movq    %rdx, %rdi
0000000000000015    rep
0000000000000016    stosq
0000000000000018    movb    $0x42, -0x28(%rbp)
000000000000001c    movl    $0x30, %eax
0000000000000021    popq    %rbp
0000000000000022    retq

rep stosq does zero 48 bytes, that is namelist[].

Or, if it is static.

: #include <nlist.h>
:
: int main(void) {
:   static struct nlist namelist[2] = {{ .n_type = 0x42 }};
:   return sizeof(namelist);
: }

(__DATA,__data) section
0000000000000020    00 00 00 00 00 00 00 00 42 00 00 00 00 00 00 00
0000000000000030    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0000000000000040    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

-- 
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