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List:       busybox
Subject:    Re: [PATCH] dhcpc.c: fix found_opts
From:       Lambrecht_Jürgen <J.Lambrecht () TELEVIC ! com>
Date:       2011-10-12 8:06:09
Message-ID: 4E954A71.8030604 () televic ! com
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On 10/11/2011 05:33 PM, Denys Vlasenko wrote:
>
> 2011/10/11 Lambrecht Jürgen <J.Lambrecht@televic.com>:
> > Hello,
> >
> > The patch below fixes a bug in networking/udhcp/dhcpc.c. Here my 
> reasoning:
> > There are 256 dhcp options supported, so 256 bits to store.
> > You want to store that in an unsigned (BITMAP define), 32b in my case.
> > So you need an unsigned array of 256/sizeoff(unsigned) == 8 elements.
>
> sizeof(unsigned) is 4, because sizeof() measures size in bytes, not bits.
>
oops, indeed (I was thinking too much in hardware ;-)
>
>
> 256/4 = 64.
>
> > In
> > the code, the define BBITS is used for this, and the bug is that *8 is
> > added to that define, resulting in an array of only 1 element (32b) to
> > store 256 bits.
>
> I disassembled this:
>
>         memset(found_opts, 0, sizeof(found_opts));
>
> and I see that this memset fills 8 words, not 1 word:
>
>    f:   b9 08 00 00 00          mov    $0x8,%ecx
>   14:   31 c0                   xor    %eax,%eax
>   16:   f3 ab                   rep stos %eax,%es:(%edi)
>
> --
> vda
>
Indeed, I was wrong - I took the wrong conclusions from my debugging..
So forget the patch.
(my problems were actually caused by not understanding 'putenv' and how 
to use it)

Thanks,
Jürgen

-- 
Jürgen Lambrecht
R&D Associate
Tel: +32 (0)51 303045    Fax: +32 (0)51 310670
http://www.televic-rail.com
Televic Rail NV - Leo Bekaertlaan 1 - 8870 Izegem - Belgium
Company number 0825.539.581 - RPR Kortrijk
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