Zephyr - failed to link mbedtls

[magdalenaszumny]

Environment

• Build System: CMake
• Operating System: Zephyr
• Operating System Version:
• Hosted Environment:

libcoap Configuration Summary

Problem Description

I am using libcoap for Zephyr with mbedtls. I have following problem during the build:
CMake Error at xxx/lib/libcoap/CMakeLists.txt:747 (target_link_libraries):
Target "coap-3" links to:

MbedTLS::mbedtls

but the target was not found. Possible reasons include:

* There is a typo in the target name.
* A find_package call is missing for an IMPORTED target.
* An ALIAS target is missing.

I checked zephyr_modules.txt in build output and I see that libcoap is before mbedtls on the list. That means that libcoap does not see mbedtls at the momen when libcoap is build.
I have other sample application, where I don't see this issue. I checked zephyr_modules.txt there and I can see that mbedtls is before libcoap.

I have some fix that ensures that Zephyr sees mbedtls when building libcoap. In module.yml in libcoap we can add:
depends:

• mbedtls

But I guess that is not generic enough, because other users might not be using mbedtls. Do you have any suggestions?

Expected Behavior

Libcoap with mbedtls can be build for Zephyr and successful build is not dependent on modules order.

Actual Behavior

Build is dependent on modules order.

Steps to reproduce

Code to reproduce this issue

Debug Logs

Other items if possible

[mrdeep1]

Is this a case of you need to add in CONFIG_MBEDTLS=y in the prj.conf file?

[magdalenaszumny]

Yes, CONFIG_MBEDTLS=y is included in prj.conf, but the order of compilation is incorrect because libcoap is built before mbedtls. libcoap tries to link to mbedtls but it is not yet available. When added "depends: -mbedtls" to module.yml then Zephyr enforces correct build order when sorting the modules for compilation. Currently Zephyr does not have enough information about the needed order and in my cases this order is incorrect (first libcoap, then mbedtls).

[mrdeep1]

What happens if you remove CONFIG_MBEDTLS=y? Then things should default to using the zephyr DTLS backend.

[magdalenaszumny]

I would like to use mbedtls backend :)

[mrdeep1]

My concern about your solution is that another zephyr user needs wolfssl support.

[magdalenaszumny]

Yes, I think that my solution is not generic enough and cannot be included in the library. But maybe you have some other idea how to solve it?

[mrdeep1]

Unfortunately not at this point. I am offline most of this week to be able to do much testing.