Re: pcap_compile() errors in libpcap beta and CVS

[George Bakos <gbakos () ists dartmouth edu>]

I agree, this is not the true root of the problem, merely a symptom fix.
However, reverting to break statements preserves all of the fixes provided
in Yamamoto's patch, and makes the examples I provided work properly.

A similar case that is still not handled properly is:

   tcpdump 'len=len' is always true
   tcpdump 'len=0 or len=len' should also be true, but fails thusly:
(000) ld       #pktlen
(001) jeq      #0x0             jt 3    jf 2
(002) jeq      x                jt 3    jf 4
(003) ret      #68
(004) ret      #0

When I compile without any peep ahead, it behaves properly in all cases. :-p

I'll keep working on the optimizer, but suggest using the patch I supplied
for the time being, to get rid of most of the problem if this is to be
released.

Is there a standard set of filters, as well as a data file & result set
for compile & optimize regression testing?

g

On Wed, 17 Dec 2003 10:04:39 -0800
Guy Harris <guy () alum mit edu> wrote:

> I've been looking at this - there is, I think, an optimizer bug
> elsewhere, and his change might merely have exposed that bug.  I haven't
> tracked it down yet, however.  (It's converting the "false" branch of
> one jeq to go to the "ret #0" when it shouldn't be.  This might also be
> the cause of a bug in the libpcap bug database on SourceForge.)
>
> His changes fix some other problems:
>
>       Date: Thu, 25 Apr 2002 07:20:47 +0900 (JST)                             
>       To: patches () tcpdump org
>       Subject: some fixes for complier and optimizer in libpcap
>       From: YAMAMOTO Takashi <yamt () mwd biglobe ne jp>
>
>       I made patches for libpcap.
>
>       it includes:
>       - make tcpdump "1 > 1" works correctly.
>       - make things unsigned as in-kernel filter does.
>       - fix a bug that prevents optimization. (and might cause bad codes)
>         eg. "1 & len == 1"
>       - fix wrong optimizations.
>         eg. "0 >> len == 1", "0 - len == 1"

-- 
George Bakos
Institute for Security Technology Studies - IRIA
Dartmouth College
gbakos () ists dartmouth edu
603.646.0665 -voice
603.646.0666 -fax
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