Re: Remove the eproto_db symbol exporting to keep the DLL delay-load feature on Windows

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

On Jun 27, 2016, at 10:56 PM, Yang Luo <hsluoyb () gmail com> wrote:

> Because of libpcap has exported the a data structure called eproto_db 
> (https://github.com/the-tcpdump-group/libpcap/blob/master/nametoaddr.c#L320), when I compiled WinDump in MSVC 
> specifying "wpcap.dll" as a delay loaded DLL, I encountered the link error 1194. The cause is here: 
> https://msdn.microsoft.com/en-us/library/w59k653y%28v=vs.80%29.aspx?f=255&MSPPError=-2147217396.
>
> Delay loading wpcap.dll is an important part for the switch between Npcap mode and WinPcap mode. And from the 
> comment, it seems that exporting this data is not very critical. So can we remove the "PCAP_API_DEF" at the line 
> beginning to disable the exporting?

What the comment says is

        * tcpdump used to import this, and it's declared as an export on
        * Debian, at least, so make it a public symbol, even though we
        * don't officially export it by declaring it in a header file.

which means that if we stop exporting it on UN*X, Debian might have to deem that an incompatible change to the ABI and 
that might cause significant disruption on Debian and its derivatives.

Other UN*Xes that ship libpcap might have a problem, especially if they have to support third-party closed-source 
binaries.

So, at minimum, we should continue to export it on UN*X.

And that might be an issue with Windows binaries as well; I suspect WinDump, for example, imports eproto_db from 
WinPcap, as it's based on an older version of tcpdump that imported it from libpcap.  I'll leave it up to you to 
determine whether introducing a possible binary incompatibility between WinPcap and Npcap is an issue.
_______________________________________________
tcpdump-workers mailing list
tcpdump-workers () lists tcpdump org
https://lists.sandelman.ca/mailman/listinfo/tcpdump-workers