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

[Yang Luo <hsluoyb () gmail com>]

OK. I will try my best to keep this structure exported, if it can't be
done, I will only remove the export on Windows.


Cheers,
Yang

On Thu, Jun 30, 2016 at 1:14 PM, Guy Harris <guy () alum mit edu> wrote:

> 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.
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