It seems that you can't just go ahead and implement your own proc_def_t for processor module - bcs ida pro sdk don`t include needed symbols, you will just get something like
1>reg.obj : error LNK2019: unresolved external symbol "public: __cdecl proc_def_t::proc_def_t(struct elf_loader_t &,class reader_t &)" (??0proc_def_t@@QEAA@AEAUelf_loader_t@@AEAVreader_t@@@Z) referenced in function "public: virtual __int64 __cdecl xxx_t::on_event(__int64,char *)" (?on_event@xxxson_t@@UEAA_J_JPEAD@Z)
1>reg.obj : error LNK2001: unresolved external symbol "public: virtual bool __cdecl proc_def_t::proc_supports_relocs(void)const " (?proc_supports_relocs@proc_def_t@@UEBA_NXZ)
1>reg.obj : error LNK2001: unresolved external symbol "public: virtual char const * __cdecl proc_def_t::proc_handle_reloc(struct rel_data_t const &,struct sym_rel const *,struct elf_rela_t const *,struct reloc_tools_t *)" (?proc_handle_reloc@proc_def_t@@UEAAPEBDAEBUrel_data_t@@PEBUsym_rel@@PEBUelf_rela_t@@PEAUreloc_tools_t@@@Z)
1>reg.obj : error LNK2001: unresolved external symbol "public: virtual bool __cdecl proc_def_t::proc_create_got_offsets(struct Elf64_Shdr const *,struct reloc_tools_t *)" (?proc_create_got_offsets@proc_def_t@@UEAA_NPEBUElf64_Shdr@@PEAUreloc_tools_t@@@Z)
1>reg.obj : error LNK2001: unresolved external symbol "public: virtual bool __cdecl proc_def_t::proc_perform_patching(struct Elf64_Shdr const *,struct Elf64_Shdr const *)" (?proc_perform_patching@proc_def_t@@UEAA_NPEBUElf64_Shdr@@0@Z)
1>reg.obj : error LNK2001: unresolved external symbol "public: virtual bool __cdecl proc_def_t::proc_can_convert_pic_got(void)const " (?proc_can_convert_pic_got@proc_def_t@@UEBA_NXZ)
1>reg.obj : error LNK2001: unresolved external symbol "public: virtual unsigned __int64 __cdecl proc_def_t::proc_convert_pic_got(class segment_t const *,struct reloc_tools_t *)" (?proc_convert_pic_got@proc_def_t@@UEAA_KPEBVsegment_t@@PEAUreloc_tools_t@@@Z)
1>reg.obj : error LNK2001: unresolved external symbol "public: virtual char const * __cdecl proc_def_t::proc_describe_flag_bit(unsigned int *)" (?proc_describe_flag_bit@proc_def_t@@UEAAPEBDPEAI@Z)
1>reg.obj : error LNK2001: unresolved external symbol "public: virtual bool __cdecl proc_def_t::proc_load_unknown_sec(struct Elf64_Shdr *,bool)" (?proc_load_unknown_sec@proc_def_t@@UEAA_NPEAUElf64_Shdr@@_N@Z)
1>reg.obj : error LNK2001: unresolved external symbol "public: virtual char const * __cdecl proc_def_t::proc_handle_dynamic_tag(struct Elf64_Dyn const *)" (?proc_handle_dynamic_tag@proc_def_t@@UEAAPEBDPEBUElf64_Dyn@@@Z)
1>reg.obj : error LNK2001: unresolved external symbol "public: virtual bool __cdecl proc_def_t::proc_is_acceptable_image_type(unsigned short)" (?proc_is_acceptable_image_type@proc_def_t@@UEAA_NG@Z)
1>reg.obj : error LNK2001: unresolved external symbol "public: virtual void __cdecl proc_def_t::proc_on_start_data_loading(struct elf_ehdr_t &)" (?proc_on_start_data_loading@proc_def_t@@UEAAXAEAUelf_ehdr_t@@@Z)
1>reg.obj : error LNK2001: unresolved external symbol "public: virtual bool __cdecl proc_def_t::proc_on_end_data_loading(void)" (?proc_on_end_data_loading@proc_def_t@@UEAA_NXZ)
1>reg.obj : error LNK2001: unresolved external symbol "public: virtual void __cdecl proc_def_t::proc_on_loading_symbols(void)" (?proc_on_loading_symbols@proc_def_t@@UEAAXXZ)
1>reg.obj : error LNK2001: unresolved external symbol "public: virtual bool __cdecl proc_def_t::proc_handle_symbol(struct sym_rel &,char const *)" (?proc_handle_symbol@proc_def_t@@UEAA_NAEAUsym_rel@@PEBD@Z)
1>reg.obj : error LNK2001: unresolved external symbol "public: virtual void __cdecl proc_def_t::proc_handle_dynsym(struct sym_rel const &,unsigned int,char const *)" (?proc_handle_dynsym@proc_def_t@@UEAAXAEBUsym_rel@@IPEBD@Z)
1>reg.obj : error LNK2001: unresolved external symbol "public: virtual int __cdecl proc_def_t::proc_handle_special_symbol(struct sym_rel *,char const *,unsigned short)" (?proc_handle_special_symbol@proc_def_t@@UEAAHPEAUsym_rel@@PEBDG@Z)
1>reg.obj : error LNK2001: unresolved external symbol "public: virtual bool __cdecl proc_def_t::proc_should_load_section(struct Elf64_Shdr const &,unsigned int,class _qstring<char> const &)" (?proc_should_load_section@proc_def_t@@UEAA_NAEBUElf64_Shdr@@IAEBV?$_qstring@D@@@Z)
1>reg.obj : error LNK2001: unresolved external symbol "public: virtual bool __cdecl proc_def_t::proc_on_create_section(struct Elf64_Shdr const &,class _qstring<char> const &,unsigned __int64 *)" (?proc_on_create_section@proc_def_t@@UEAA_NAEBUElf64_Shdr@@AEBV?$_qstring@D@@PEA_K@Z)
1>reg.obj : error LNK2001: unresolved external symbol "public: virtual char const * __cdecl proc_def_t::calc_procname(unsigned int *,char const *)" (?calc_procname@proc_def_t@@UEAAPEBDPEAIPEBD@Z)
1>reg.obj : error LNK2001: unresolved external symbol "public: virtual unsigned __int64 __cdecl proc_def_t::proc_adjust_entry(unsigned __int64)" (?proc_adjust_entry@proc_def_t@@UEAA_K_K@Z)
1>D:\ida75\procs\xxx64.dll : fatal error LNK1120: 21 unresolved externals
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