On 08.7.2010 11:02:10, Maksym Kryzhanovskyy wrote:
> On 08.7.2010 02:37:35, Denys Vlasenko wrote:
> > On Wednesday 07 July 2010 12:58, Maksym Kryzhanovskyy wrote:
> > > Hi Denis,
> > >
> > > can we use the __builtin_expect function in busybox?
> > > In the previous patch for ifplugd it might be usefull
> > > (see attachment).
> >
> > - if (!G.detect_link_func) {
> > + if (__builtin_expect(G.detect_link_func == NULL, 0)) {
> >
> > I don't see any changes in size, only obfuscated code.
>
.. you're right it is for nothing, detect_link with __builtin_expect
is the same as without it. It is seen from the code in attachment.
>
> Yes, it's not for reducing the size of ifplugd, but we wanted to ask gcc to
> optimize the if statment for a negative result (moreover, it costs nothing in
> terms of size):
>
> if (!G.detect_link_func) { // predominantly negative throughout life of
> ifplugd
>
>
> This may be unlikely() if it is more readable as Marek Polacek
> and Bernhard Fischer-Reutner offers:
>
> #define unlikely(x) __builtin_expect(!!(x), 0)
> if (unlikely(G.detect_link_func == NULL)) {
>
>
> If it is actually needed..
>
>
> Max.
>
> > --
> > vda
> >
> >
> >
>
> detect_link:
pushl %edi
pushl %esi
pushl %ebx
subl $4, %esp
movl ptr_to_globals, %ebx
cmpb $0, 2(%ebx)
movl option_mask32, %eax
jne .L66
andl $65536, %eax
cmpl $1, %eax
sbbl %eax, %eax
jmp .L68
.L66:
testb $1, %al
jne .L69
call up_iface
.L69:
cmpl $0, 32(%ebx)
jne .L70
movb 3(%ebx), %al
testb %al, %al
jne .L71
movb logmode, %dl
xorl %esi, %esi
.L74:
movb $0, logmode
movl method.8477+4(,%esi,8), %edi
movb %dl, (%esp)
call *%edi
movb (%esp), %dl
movb %dl, logmode
cmpb $-1, %al
je .L72
movl %edi, 32(%ebx)
pushl method.8477(,%esi,8)
pushl $.LC14
movb %al, 8(%esp)
call bb_error_msg
popl %edi
popl %eax
movb (%esp), %al
jmp .L73
.L72:
incl %esi
cmpl $5, %esi
jne .L74
jmp .L75
.L71:
movsbl %al,%eax
movl method.8477-4(,%eax,8), %eax
movl %eax, 32(%ebx)
.L70:
call *32(%ebx)
.L76:
cmpb $-1, %al
jne .L73
.L75:
movl option_mask32, %edx
xorl %eax, %eax
testb $8, %dl
jne .L73
movb $1, %al
andb $16, %dl
jne .L73
movb $-1, %al
cmpb $0, 3(%ebx)
jne .L73
pushl $.LC15
call bb_error_msg
movb $-1, %al
popl %esi
.L73:
movb (%ebx), %dl
cmpb %dl, %al
je .L68
movb %dl, 1(%ebx)
movb %al, (%ebx)
.L68:
popl %ecx
popl %ebx
popl %esi
popl %edi
ret
detect_link:
pushl %edi
pushl %esi
pushl %ebx
subl $4, %esp
movl ptr_to_globals, %ebx
cmpb $0, 2(%ebx)
movl option_mask32, %eax
jne .L66
andl $65536, %eax
cmpl $1, %eax
sbbl %eax, %eax
jmp .L68
.L66:
testb $1, %al
jne .L69
call up_iface
.L69:
cmpl $0, 32(%ebx)
jne .L70
movb 3(%ebx), %al
testb %al, %al
jne .L71
movb logmode, %dl
xorl %esi, %esi
.L74:
movb $0, logmode
movl method.8477+4(,%esi,8), %edi
movb %dl, (%esp)
call *%edi
movb (%esp), %dl
movb %dl, logmode
cmpb $-1, %al
je .L72
movl %edi, 32(%ebx)
pushl method.8477(,%esi,8)
pushl $.LC14
movb %al, 8(%esp)
call bb_error_msg
popl %edi
popl %eax
movb (%esp), %al
jmp .L73
.L72:
incl %esi
cmpl $5, %esi
jne .L74
jmp .L75
.L71:
movsbl %al,%eax
movl method.8477-4(,%eax,8), %eax
movl %eax, 32(%ebx)
.L70:
call *32(%ebx)
.L76:
cmpb $-1, %al
jne .L73
.L75:
movl option_mask32, %edx
xorl %eax, %eax
testb $8, %dl
jne .L73
movb $1, %al
andb $16, %dl
jne .L73
movb $-1, %al
cmpb $0, 3(%ebx)
jne .L73
pushl $.LC15
call bb_error_msg
movb $-1, %al
popl %esi
.L73:
movb (%ebx), %dl
cmpb %dl, %al
je .L68
movb %dl, 1(%ebx)
movb %al, (%ebx)
.L68:
popl %ecx
popl %ebx
popl %esi
popl %edi
ret
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