[asterisk-dev] Problems with custom C-file: undefined reference

Sat Dec 17 00:31:49 CST 2016

Because this problem most likely being the last barrier to finish my
project, I will explain it once again in a little more detail.

There are the following files that I think may be important to solve the
problem:
*channels/chan_sip.c*
*channels/sip/include/system.h*
*channels/system.c*
*channels/system.exports.in <http://system.exports.in>*

I want *system.c* to export several functions, one of them is
*sys_system_get_our_address(struct ast_sockaddr *us).*

That function is implemented in *system.c, *gets called in *chan_sip.c*
and it's prototype is declared in *system.h*.

To export that function, I created the file system.exports.in in channels/,
which content is the following:
{
global:
LINKER_SYMBOL_PREFIXsys_*;
LINKER_SYMBOL_PREFIX_IO_stdin_used;
local:
*;
};

I tried a *make dist-clean* and a complete recompilation afterwards. The
build system doesn't create the file *system.exports*, but it creates
*chan_sip.exports* which is in the same folder. I dig into to the system
and found *build-tools/make_linker_version_script* which probably creates
the exports files.
test -f ${1}.exports.in && ${AWK} "{sub(\"LINKER_SYMBOL_PREFIX\",
\"${2}\"); print;}" ${1}.exports.in > ${1}.exports && exit 0
test -f ${1}.exports.in || rm -f ${1}.exports && cp ${3}/default.exports
${1}.exports && exit 0

Can anyone see any mistakes I make? Thank you very much.

Regards,
Julian Fleischhauer

2016-12-12 11:40 GMT+01:00 Julian Fleischhauer <
julian.fleischhauer at stud.uni-due.de>:

> Thank you for this simple solution, it solved the last problem.
>
> Another issue arised: Before, system.c was in the main/ directory and used
> the project wide exports file to export its functions, now it's in
> channels/ where apparantly doesn't exist such a file.
> I created *system.exports.in <http://system.exports.in>* in channels/ to
> export the functions but the Asterisk build system does not automatically
> generate the *system.exports* file and manually creating it doesn't work
> either.
>
> *system.h*
> void ast_system_get_address(struct ast_sockaddr *us);
>
> *system.c*
> #include "asterisk/system.h"
>
> void ast_system_get_address(struct ast_sockaddr *us)
> {
>    ...
> }
>
> *chan_sip.c*
> #include "asterisk/system.h"
>
> ast_system_get_address(us);
>
> 2016-12-09 18:42 GMT+01:00 Corey Farrell <git at cfware.com>:
>
>> I'm not sure what you're trying to accomplish but this is not the
>> approach I'd take for expanding chan_sip.  My advice is to simply put your
>> system.c into channels/sip.  This will automatically link it into the
>> binary chan_sip module, but allow you to keep your source code in a
>> separate file.  I believe MODULEINFO (for any added dependencies) and
>> possibly a call to your init/cleanup would be the only changes you'd need
>> to make in chan_sip.c.  All non-static symbols in chan_sip.c and
>> channels/sip/*.c are available across all sources of chan_sip.so without
>> needing chan_sip.exports.in or AST_MODFLAG_GLOBAL_SYMBOLS.
>>
>> The only exception is if you need to call chan_sip functions from another
>> existing module, then you will have to export the symbols.  To do this you
>> have to tell the linker (via chan_sip.exports.in) and you have to tell
>> the module loader.  AST_MODULE_INFO at the very end of chan_sip.c would
>> need AST_MODFLAG_GLOBAL_SYMBOLS so the module loader knows to share the
>> globals:
>>
>> AST_MODULE_INFO(ASTERISK_GPL_KEY, AST_MODFLAG_GLOBAL_SYMBOLS
>> | AST_MODFLAG_LOAD_ORDER, "Session Initiation Protocol (SIP)",
>>
>>
>>
>> On Fri, Dec 9, 2016 at 10:50 AM, Julian Fleischhauer <
>> julian.fleischhauer at stud.uni-due.de> wrote:
>>
>>> I could resolve the XML and pcap issues, but still have problems
>>> concerning "sip_get_header()". I don't want to rename the function since
>>> it's a frequently used function in chan_sip.c, I therefore defined an .
>>> exports.in file. I don't know if Mr. Michelson understood me correctly,
>>> but I think chan_sip.c exports "sip_get_header()" (doesn't it?) so I
>>> modified *chan_sip.exports.in <http://chan_sip.exports.in>* so it looks
>>> like
>>> {
>>> global:
>>> LINKER_SYMBOL_PREFIXsip_get_header;            // I also tried
>>> LINKER_SYMBOL_PREFIXsip_*;
>>> LINKER_SYMBOL_PREFIX_IO_stdin_used;
>>> local:
>>> *;
>>> };
>>> But it doesn't work. I did the same with *system.exports.in
>>> <http://system.exports.in>*, without success.
>>>
>>>
>>> Sorry for the badly formatted last mail. I will post the updated file
>>> structure again below.
>>>
>>> *sip.h*
>>> const char *sip_get_header(const struct sip_request *req, const char
>>> *name);
>>>
>>> *system.h*
>>> #include "asterisk/netsock2.h"
>>>
>>> void ast_some_function(struct sip_pvt *p, struct ast_sockaddr *addr);
>>>
>>> *system.c*
>>> #include "asterisk/system.h"
>>> #include "asterisk/sip.h"
>>>
>>> void ast_some_function(struct sip_pvt *p, struct ast_sockaddr *addr)
>>> {
>>>    ast_copy_string(touser, sip_get_header(req, "To"),
>>> strlen(sip_get_header(req, "To")) + 1);
>>> }
>>>
>>> *chan_sip.c*
>>> #include "asterisk/system.h"
>>> #include "asterisk/sip.h"
>>>
>>> ast_some_function(p, addr);
>>>
>>>
>>> Best regards,
>>> Julian Fleischhauer
>>>
>>> 2016-12-06 18:35 GMT+01:00 Mark Michelson <mmichelson at digium.com>:
>>>
>>>> On 12/05/2016 04:53 PM, Julian Fleischhauer wrote:
>>>>
>>>>> Hey all,
>>>>>
>>>>> I have a problem using a custom C-file. The error ouput received when
>>>>> compiling is given below.
>>>>>
>>>>> error output
>>>>> .../system.c:1330: undefined reference to `XML_ParserCreate'
>>>>> ...
>>>>> .../system.c:1465: undefined reference to `sip_get_header'
>>>>> ...
>>>>> .../system.c:1608: undefined reference to `pcap_lookupnet'
>>>>> ...
>>>>>
>>>>>
>>>>> Before, I had all code in chan_sip.c. I want to transfer the code into
>>>>> a separate file (system.c) now. The dependencies given below MODULEINFO are
>>>>> customly set and worked fine when used in chan_sip.c. Can anyone figure out
>>>>> if something else has to be added somewhere? The code is quoted below:
>>>>>
>>>>> sip.h
>>>>> const char *sip_get_header(const struct sip_request *req, const char
>>>>> *name);
>>>>>
>>>>> system.h
>>>>> #include "asterisk/netsock2.h"
>>>>>
>>>>> void ast_some_function(struct sip_pvt *p, struct ast_sockaddr *addr);
>>>>>
>>>>> system.c
>>>>> /*** MODULEINFO
>>>>>      <depend>sqlite3</depend>
>>>>>      <depend>expat</depend>
>>>>>      <depend>pcap</depend>
>>>>>     <support_level>extended</support_level>
>>>>> ***/
>>>>>
>>>>> #include "asterisk/system.h"
>>>>> #include "asterisk/sip.h"
>>>>>
>>>>> void ast_some_function(struct sip_pvt *p, struct ast_sockaddr *addr)
>>>>> {
>>>>>     xmlParser = XML_ParserCreate(NULL);
>>>>>    ...
>>>>>    ast_copy_string(touser, sip_get_header(req, "To"),
>>>>> strlen(sip_get_header(req,       "To"))+1);
>>>>>    ...
>>>>>    pcap_lookupnet(pcapDev, &netp, &maskp, errbuf);
>>>>> }
>>>>>
>>>>> chan_sip.c
>>>>> #include "asterisk/system.h"
>>>>> #include "asterisk/sip.h"
>>>>>
>>>>> ast_some_function(p, addr);
>>>>>
>>>>>
>>>>> Thank you for any help!
>>>>>
>>>>> Regards,
>>>>> Juliannn
>>>>>
>>>>> I can explain why sip_get_header() is causing a problem. In order for
>>>> functions to be callable from other modules, they need to be explicitly
>>>> exported. This is why you'll see files like res/res_agi.exports.in,
>>>> which define functions that can be called globally from that module. You
>>>> have a couple of options here:
>>>>
>>>> * Define a .exports.in file for your system.c file that exports the
>>>> sip_get_header() function.
>>>> * Change "sip_get_header()" to "ast_sip_get_header()". Assuming that
>>>> system.c is in the main/ directory, there is a project-wide exports file
>>>> that makes it so any function starting with "ast" can be called externally.
>>>>
>>>> Regarding the XML and pcap issues, the issues are either that
>>>> * You're not #including the necessary files.
>>>> * The libraries are not being linked during compilation.
>>>>
>>>> The first problem is easy to fix: just #include the right files :). The
>>>> second problem is a bit more tricky because you'll need to dig into
>>>> Makefiles and try to figure out how libraries get linked when Asterisk is
>>>> built.
>>>>
>>>>
>>>> --
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>>>>
>>>>
>>>
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>>
>>
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