Re: Modular arithmetic

[Guy Harris <guy () alum mit edu>]

On Sep 10, 2012, at 3:41 AM, "David Laight" <David.Laight () ACULAB COM> wrote:

> > > What about the other OS - eg all the BSDs?
> > > I had a vague idea that BPF was supposed to be reasonable portable.
> >
> > Yes, does it mean BPF is frozen ?
> >
> > Or is BSD so hard to update these days ?
>
> Not really - but it some other places that need updating in order
> to make this useful for cross-platform tools (like tcpdump).
>
> The 'real fun (tm)' happens when NetBSD tries to run Linux binaries
> that include the Linux libpcap.

Additional fun happens when a Linux system with a kernel that doesn't have the mod instruction tries to run Linux 
binaries that include a Linux libpcap that generates code using the mod instruction; this is not a BSD-vs.-Linux issue, 
it's a "kernel that lacks the mod instruction vs. libpcap that generates code that includes the mod instruction" issue.

BSD/OS X, Linux, Solaris, and the WinPcap driver need, if they adopt new BPF instructions, to have a mechanism by which 
libpcap (or anything else using BPF filtering) can inquire about the capabilities of the OS BPF interpreter; libpcap 
would use that to determine what code to generate if generating code for the in-kernel BPF interpreter.

(Please reply to tcpdump-workers () lists tcpdump org as well as to netdev () vger kernel org, so that people not on 
both of those lists can follow the discussion.  Messages from non-members of tcpdump-workers to tcpdump-workers 
shouldn't bounce, but they do need to be approved by a moderator; Michael, if you want to at least temporarily turn the 
flood on for my e-mail address, so I can help moderate, go ahead.)
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