Unable to link mbed-os aginst multiple applications with custom configuration

[nat45928]

Description of defect

I am unable to build a library from mbed-os to link against when using a custom mbed_app.json because the mbed_config.h produced with the --library option differs from a normally built application. This causes the application to fail to boot.

Additional Background

I have a project which produces multiple binary applications from a single codebase. I have been using the compiler --source option to change which files are selected by mbed-os. For example (where folders foo and bar contain different main.cpp files):

1. mbed compile --app-config mbed_app.json --source foo --source mbed-os builds foo
2. mbed compile --app-config mbed_app.json --source bar --source mbed-os builds bar

However, this takes a long time due to the rebuild of mbed-os library for each application. I would like to use the provided --library option to build mbed-os once then link my two applications aginst it. Similar to:

1. mbed compile --app-config mbed_app.json --source mbed-os --build BUILD/mbed-os --library --no-archive builds the mbed-os library
2. mbed compile --app-config mbed_app.json --source foo --source BUILD/mbed-os --build BUILD/foo builds foo
3. mbed compile --app-config mbed_app.json --source bar --source BUILD/mbed-os --build BUILD/bar builds bar

This process works but produces binaries that do not execute. Upon digging the resulting mbed_config.h for step 1 vs steps 2 and 3 differ. Digging into the tools folder it appears that build.py does not respect the app-config CLI parameter.

Is this workflow expected to work, is there a better workflow that should be followed?

Target(s) affected by this defect ?

NUCLEO_F767ZI

Toolchain(s) (name and version) displaying this defect ?

GCC_ARM, 9-2019-q4-major, 9.2.1 20191025

What version of Mbed-os are you using (tag or sha) ?

d5f034b

What version(s) of tools are you using. List all that apply (E.g. mbed-cli)

mbed-cli, 1.10.2

How is this defect reproduced ?

1. Create a fresh project.
2. Create / edit the mbed_app.json configuration to change a parameter (platform.stdio-baud-rate for example).
3. Build mbed-os using mbed compile --app-config mbed_app.json --source mbed-os --build BUILD/mbed-os --library --no-archive
4. Build app1 using mbed compile --app-config mbed_app.json --source foo --source BUILD/mbed-os --build BUILD/foo
5. The application does not execute correctly.

[0xc0170]

cc @ARMmbed/mbed-os-tools

[nat45928]

It seems like there are a few changes needed:

1. mbed-cli's mbed.py needs to pass --app_config to build.py here.
2. build.py needs to accept --app_config by calling get_default_options_parser(add_app_config=True) here.
3. build.py needs to pass app_config to the build_library() methods here.

Making these changes locally allows me to build working applications. Is there anything wrong with this approach?

[0xc0170]

Thanks @nat45928 for the details how to fix. We will review

[nat45928]

@0xc0170 Is the approach I proposed appropriate? If so I am happy to open PRs to do the work. I would really like this workflow to be functional.

[ciarmcom]

Thank you for raising this detailed GitHub issue. I am now notifying our internal issue triagers.
Internal Jira reference: https://jira.arm.com/browse/IOTOSM-2134

[0xc0170]

@nat45928 starting the previous year we started working on moving to CMake based build. I'll close this and we should get a new issue with new tools if this use case is not supported.
This should be feasible with the new tools (not using --library command but rather using cmake STATIC or OBJECT libraries).