Using custom target with compiled object files as input?

[aydinmercan]

I am currently experimenting meson as an alternative to replace autoconf in an existing project. While the port is relatively straightforward and better (hurray meson!), userspace probing with DTrace is awkward to use in meson.

In FreeBSD and Solaris, you need the compiled object files and the probe file to generate the ELF file you link with the final executable.

Because meson doesn't have an object library, I had to make a library without probing, extract the objects for DTrace and then finally link every object again inside another library. This is also Postgres does but it had a massive build time penalty when I tried it with LTO.

Is there another method that I have missed without adding additional functionality to meson? (That being said, I am willing to give it a shot or try an draft implementation if its on the roadmap 😺 )

# An example way of dtrace support
foo_unprobed = shared_library(
    'foo_unprobed',
    foo_sources,
    # and the rest
)

foo_probe = custom_target(
    'foo-usdt',
    input: [
        'probes.d',
        foo_unprobed.extract_objects('bar.c', 'baz.c'),
    ],
    output: 'probes.o',
    command: [ dtrace, '-G', '-o', '@OUTPUT@', '-s', '@INPUT@' ],
)

shared_library(
     'foo',
     foo_probe,
     objects: foo_unprobed.extract_all_objects(recursive: false),
     install: true,
     # and the rest again.....
)