Re: where is CFG generated?

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

Hui.Ning () utstar com wrote:

> For tcpdump, I am trying to find out where  is CFG ( call flow graph 
> structure, which is used for further optimization ) generated? during 
> parsing stage or after the parsing stage?

*Currently*, the CFG is generated by pcap_parse() (and by a call to 
gen_retblk()), which means it's generated during the parsing stage.  See 
pcap_compile() in gencode.c.

(This is in libpcap, not tcpdump.  Tcpdump has no code to parse a filter 
and generate a CFG or generate BPF code from that; it calls libpcap to 
do that (as do many other applications).)

This is *NOT* guaranteed to remain true forever.  The CFG might, in the 
future, be generated elsewhere; there might, for example, be a split 
between the parser and the code generator.

Why do you need to know where it's done?  (As I indicated, it's not 
necessarily going to be done in the same place forever.  You shouldn't 
write code that assumes pcap_compile() works in a particular fashion.)
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