Re: libpcap detection and linking in tcpdump

[Guy Harris via tcpdump-workers <tcpdump-workers () lists tcpdump org>]

> --- Begin Message ---
>
>
> From: Guy Harris <gharris () sonic net>
>
> Date: Fri, 22 Jan 2021 19:11:16 -0800
>
> On Jan 22, 2021, at 2:54 PM, Denis Ovsienko via tcpdump-workers <tcpdump-workers () lists tcpdump org> wrote:
>
> > I have tested it again with the current master branches of libpcap and
> > tcpdump. Both builds (with and without libpcap0.8-dev) now complete
> > without errors.
> >
> > However, in both cases the installed tcpdump fails to run because it
> > is linked with libpcap.so.1. Which, as far as I can remember,
> > previously somehow managed to resolve to the
> > existing /tmp/libpcap/lib/libpcap.so.1, but not amymore:
> >
> > $ /tmp/libpcap/bin/tcpdump --version
> > /tmp/libpcap/bin/tcpdump: error while loading shared libraries:
> > libpcap.so.1: cannot open shared object file: No such file or directory
> >
> > $ ldd /tmp/libpcap/bin/tcpdump
> >       linux-vdso.so.1 (0x00007ffdc7ffe000)
> >       libpcap.so.1 => not found
> >       libcrypto.so.1.1 => /usr/lib/x86_64-linux-gnu/libcrypto.so.1.1
> > (0x00007f34522ac000)
> >       libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6
> > (0x00007f3451ebb000)
> >       libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2
> > (0x00007f3451cb7000)
> >       libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0
> > (0x00007f3451a98000)
> >       /lib64/ld-linux-x86-64.so.2 (0x00007f3452c6f000)
> >
> > $ /tmp/libpcap/bin/pcap-config --libs
> > -L/tmp/libpcap/lib -Wl,-rpath,/tmp/libpcap/lib -lpcap
>
> So that *should* cause /tmp/libpcap/lib to be added to the executable's path, which *should* cause it to look in 
> /tmp/libpcap/lib for shared libraries.
>
> So, if there's a /tmp/libpcap/lib/libpcap.so.1 file, that's not happening, somehow.
>
> I'll try experimenting with one of my Ubuntu VMs.
>
> In the meantime, for some fun head-exploding reading, take a look at
>
>         https://en.wikipedia.org/wiki/Rpath
>
> and perhaps some other documents found by a search for
>
>         lpath rpath linux
>
> --- End Message ---
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