On Tue, Feb 20, 2024 at 6:09 PM R Massink <robin....@gmail.com> wrote:
> Hello, > > I've been active in creating a dissector for IEC61850, which is mapped on > top of mms. There is an integrated mms dissector that I'm using as a > template, while mapping all mms names to the IEC61850 equivalent. I have > been able to successfully use asn2wrs.py to generate a packet dissector > from the .cnf and .asn files, and can build a static wireshark executable > with my dissector included. > > However, I'm now trying to get the same dissector to work as an external > plugin, so it can be loaded by others into their wireshark without having > to use my compiled version of wireshark. > > While the external plugin compiled fine, i'm running into the problem that > the dissector_acse_* external symbols cannot be > resolved(dissect_acse_EXTERNALt is the first one) during runtime. The > dissector relies on these symbols from epan/dissectors/packet-acse.c, and > as statically build dissector they can of course be resolved. But when the > plugin loads externally during runtime(manual or automatic), the symbol > cannot be resolved anymore, while I can find it in libwireshark.so, which > is in turn loaded into memory by the wireshark process. > > I was not able to find other wireshark examples where external plugins > relied on symbols from statically linked dissectors. Is what I want simply > not possible, and should I include all acse dissector, and sub dependencies > as well in my plugin(lots of code duplication), or am I building the plugin > not correct or missing a linker flag? > The issue is not exactly in your plugin, but in the other dissector. Example where external plugins use symbols from dissectors in the main tree: opcua/opcua.c uses tcp_dissect_pdus from epan/dissectors/packet-tcp.h By default symbols are not visible. To make a symbol visible, it must have WS_DLL_PUBLIC, which is defined in include/ws_symbol_export.h (See some comments here: https://gitlab.com/wireshark/wireshark/-/blob/master/CMakeLists.txt#L1087 ) WS_DLL_PUBLIC void tcp_dissect_pdus(...); For a ASN.1 generated dissector, to cause an existing symbol to be exported, look at this commit: https://gitlab.com/wireshark/wireshark/-/commit/7ce05b9dd77741bf28a1efece8429f43982e7fe2 Where I altered the .cnf file for the x509af dissector so that dissect_x509af_Certificate got the WS_DLL_PUBLIC attribute added to it by the asn2wrs.py process. Cheers, John Thacker
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