More dkms fixes for exact cc compiler

[Dimitri John Ledkov]

[ Impact ]

 * Previously https://bugs.launchpad.net/ubuntu/+source/dkms/+bug/1991664 has fixed up some dkms modules that use makefiles without setting a CC= variable inside them. However, there is a class of dkms modules that set a CC= variable inside the makefile, and then the environment variable is ignored, thus resulting in hwe-5.19 dkms modules to FTBFS.

 * Fix those by setting MAKEFLAGS="--environment-overrides" to really ensure that environmental variable compiler is really being used.

Observe the following:

$ cat Makefile.just-cc
all:
 echo $(CC)

$ cat Makefile.cc-set
CC=cc-set-in-makefile
all:
 echo $(CC)

# cmdline override works in both cases

$ make -f Makefile.just-cc CC=make-var-cmdline
echo make-var-cmdline
make-var-cmdline

$ make -f Makefile.cc-set CC=make-var-cmdline
echo make-var-cmdline
make-var-cmdline

# environment/shell variable override only works in one of them

$ CC=env-cc make -f Makefile.just-cc
echo env-cc
env-cc

$ CC=env-cc make -f Makefile.cc-set
echo cc-set-in-makefile
cc-set-in-makefile

# unless environment-overrides is set

$ MAKEFLAGS=--environment-overrides CC=env-cc make -f Makefile.cc-set
echo env-cc
env-cc

[ Test Plan ]

 * Divert /usr/bin/gcc to /bin/false

   $ sudo ln -sf /bin/false /usr/bin/gcc

 * Install a v5.19 kernel that must be built with gcc-12 and a dkms module that uses a CC variable set inside its makefile

   $ sudo apt install linux-virtual-hwe-22.04-edge gost-crypto-dkms

 * Check that dkms status has the module successfully installed for v5.19 kernel

   $ dkms status

[ Where problems could occur ]

 * dkms cleans environment of all tool-chain related variables already, but MAKEFLAGS=--environment-overrides may result in additional/new/unexpected variables leaking into the dkms module build, which were previously ignored.

 * A better solution might be for our kernel builds to emit a makefile snippet that is included by the Kbuild makefiles, but that too will only cover a subset of dkms modules, not all of them.

 * It might be nice if environment-overrides command line option of make accepted a list of allowed variables that are desired to be honored from the environment.

[ Other Info ]

 * Any better suggestions of how to handle toolchain export would be welcome here, as this is starting to be silly.

[Launchpad Janitor (janitor)]

This bug was fixed in the package dkms - 3.0.8-3

---------------
dkms (3.0.8-3) unstable; urgency=high

  * Revert back to 3.0.8-1 behavior to prevent breakages for sid users
    (Closes: #1025214, #1025171)

 -- Aron Xu <email address hidden> Fri, 02 Dec 2022 19:49:16 +0800

[Aron Xu (happyaron)]

Re-open because 3.0.8-3 has restored to old behavior.

[Utkarsh Gupta (utkarsh)]

Ubuntu 22.10 (Kinetic Kudu) has reached end of life, so this bug will not be fixed for that specific release.