Introduce a makefile generator

[gilles-peskine-arm]

First step towards #85.

Introduce a Python script that generates a makefile.

The design is heavily based on mbedtls-prepare-build. Most of the code is copied from there, but I took the opportunity to clean it up.

This is incomplete and not yet usable for daily work. I don't want to put further time into it until the design and current code is approved.

Current features:

• Supported targets: lib, clean, help, .
• Has correct dependencies.
• Supports in-tree and out-of-tree builds.
• The makefile generation relies only on Python ≥3.5.
• The makefile relies only on POSIX make.
• Generates include/tf_psa_crypto/version.h. This part is very ugly because the template file's format relies heavily on CMake, and I think the best way format would be to change the way this template works. But that's a job for a follow-up.
• You can use custom configuration files in an out-of-tree build, but it requires manual intervention.

Features to be added in follow-ups:

• Support programs and tests.
• Good support for a different configuration (*config.h) in the build tree.
• Improve support for customizing CFLAGS and such.
• Windows support.
• Abbreviate commands in the make output.
• libtestdriver1
• Support for option presets (e.g. an easy way to request an Asan build)?
• Transparently generate the makefile if using GNU make (maybe BSD make too?).

[gilles-peskine-arm]

we already have a makefile generator system, in CMake.

Yes, but it's not good at its job.

I would prefer to ship a very simple hand-written Makefile. We can be conservative about dependencies if that's a concern, i.e. rebuild everything if a .h file changes, etc.

That might be ok for users, but it's no good for maintainers. Part of the reason I wrote mbedtls-prepare-build is to save time for myself. Even as the sole user, it's been well worth the time.

[ronald-cron-arm]

I am not sure about what you mean by "First step towards https://github.com/Mbed-TLS/TF-PSA-Crypto/issues/65."? The test components referenced by issue 65 use specific C compiler flags but having played a bit with it it seems possible to do that with cmake using something like cmake -DCMAKE_C_FLAGS=String:"-Werror -Wall -Wextra -mpclmul -msse2 -maes" .. for example.

[gilles-peskine-arm]

I am not sure about what you mean by "First step towards #65."?

Typo: I meant #85.

[ronald-cron-arm]

I am not sure about what you mean by "First step towards #65."?

Typo: I meant #85.

Ah, I could have guessed that, thanks.

[gilles-peskine-arm]

Another thing that doesn't work with cmake (both in mbedtls and in tf-psa-crypto):

$ rm programs/psa/psa_constant_names
$ make programs/psa/psa_constant_names
make: *** No rule to make target 'programs/psa/psa_constant_names'.  Stop.

Running make builds everything, but I have no idea how to build a specific program.

[ronald-cron-arm]

Another thing that doesn't work with cmake (both in mbedtls and in tf-psa-crypto):

$ rm programs/psa/psa_constant_names
$ make programs/psa/psa_constant_names
make: *** No rule to make target 'programs/psa/psa_constant_names'.  Stop.

Running make builds everything, but I have no idea how to build a specific program.

In CMake files we define the psa_constant_names target, thus make psa_constant_names just builds the psa_const_names program.