Re: [lwip-users] Errors during build of lwip in Windows

[Simon Goldschmidt]

Am 17. April 2023 08:38:56 MESZ schrieb Giuseppe Modugno 
<giuseppe.modugno.loqed@gmail.com>:
>Il 15/04/2023 01:58, Giuseppe Modugno ha scritto:
>[...]
>> Now I enabled LWIP_MQTT_APP and I receive the following errors during build:
>>
>> [ 99%] Linking C executable example_app.exe
>> liblwipcontribexamples.a(mqtt_example.obj): In function `mqtt_connection_cb':
>> C:/temp/lwip/contrib/examples/mqtt/mqtt_example.c:100: undefined reference 
>> to `mqtt_sub_unsub'
>> C:/temp/lwip/contrib/examples/mqtt/mqtt_example.c:104: undefined reference 
>> to `mqtt_sub_unsub'
>> liblwipcontribexamples.a(mqtt_example.obj): In function `mqtt_example_init':
>> C:/temp/lwip/contrib/examples/mqtt/mqtt_example.c:116: undefined reference 
>> to `mqtt_client_new'
>> C:/temp/lwip/contrib/examples/mqtt/mqtt_example.c:118: undefined reference 
>> to `mqtt_set_inpub_callback'
>> C:/temp/lwip/contrib/examples/mqtt/mqtt_example.c:123: undefined reference 
>> to `mqtt_client_connect'
>> collect2.exe: error: ld returned 1 exit status
>> mingw32-make.exe[2]: *** [CMakeFiles\example_app.dir\build.make:128: 
>> example_app.exe] Error 1
>> mingw32-make.exe[1]: *** [CMakeFiles\Makefile2:358: 
>> CMakeFiles/example_app.dir/all] Error 2
>> mingw32-make.exe: *** [Makefile:135: all] Error 2
>>
>> I couldn't understand why, because mqtt.c is really compiled and linked in 
>> liblwipallapps.a.
>
>I think I understood. In CMakeLists.txt there's the following line:
>
>target_link_libraries(example_app ${LWIP_SANITIZER_LIBS} lwipallapps 
>lwipcontribexamples lwipcontribapps lwipcontribaddons lwipcontribportwindows 
>lwipcore lwipmbedtls)
>
>I don't know exactly why, but the problem disappeared in my build system after 
>postponing lwipallapps, such as:
>
>target_link_libraries(example_app ${LWIP_SANITIZER_LIBS} lwipcontribexamples 
>lwipallapps lwipcontribapps lwipcontribaddons lwipcontribportwindows lwipcore 
>lwipmbedtls)
>

That's a known problem of the gnu linker: order of libraries is important!

>
>> Lastly another strange behaviour. If I enable LWIP_HTTPD_APP, the build 
>> process is ok, but I can't see the web page on the browser when I type the 
>> URL http://192.168.1.200.
>[...]
>
>I suspect there's a problem with WinPcap libraries. If I try to connect to the 
>http server from another machine, it works. Even ping to lwip doesn't work 
>from the Windows host machine.
>
>Do you know how this can be solved?

When talking loopback to the application, checksums are not generated as the 
windows driver or hardware generates them. Either you turn off that option in 
the windows driver or you disable checksum checks in lwip.

Regards,
Simon