netdev - Re: [PATCH] net: bpf_jit: fix divide by 0 generation

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Date:	Thu, 19 Jan 2012 09:07:44 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Phil Oester <kernel@...uxace.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: [PATCH] net: bpf_jit: fix divide by 0 generation

Le mercredi 18 janvier 2012 à 17:01 +0100, Eric Dumazet a écrit :
> Le mercredi 18 janvier 2012 à 07:57 -0800, Phil Oester a écrit :
> 
> > Got the following output after applying this fix (no panic this time):
> > 
> > proglen=231 != oldproglen=235
> > bpb_jit_compile fatal error
> > 
> > Filter being used is 'not net a.b.x.112/28 and not net a.b.y.112/28'
> 

By the way, libcap gives following code, not optimal

(000) ldh      [12]
(001) jeq      #0x800           jt 2	jf 14
(002) ld       [26]
(003) and      #0xfffffff0
(004) jeq      #0x1020340       jt 28	jf 5
(005) ld       [26]
(006) and      #0xfffffff0
(007) jeq      #0x1021480       jt 28	jf 8
(008) ld       [30]
(009) and      #0xfffffff0
(010) jeq      #0x1020340       jt 28	jf 11
(011) ld       [30]
(012) and      #0xfffffff0
(013) jeq      #0x1021480       jt 28	jf 29

...

could be :

(000) ldh      [12]
(001) jeq      #0x800           jt 2	jf 10

(002) ld       [26]
(003) and      #0xfffffff0
(004) jeq      #0x1020340       jt ok	jf 5
(005) jeq      #0x1021480       jt ok	jf 6

(006) ld       [30]
(007) and      #0xfffffff0
(008) jeq      #0x1020340       jt ok	jf 9
(009) jeq      #0x1021480       jt ok	jf ret0

...



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