Recovering an original or exec path from a repository

[Garrett Kajmowicz]

I'm working on getting out-of-tree linux kernel modules to build. One of the challenges I face is in passing the kernel tree directory path to the Kbuild system.

In my WORKSPACE file I have:

new_local_repository(

    name = "kernel_source_host",

    path = "/storage/infra/kernel_release/linux-4.14.173-src/",

    build_file = "BUILD.generic-kernel",

)

In the BUILD.generic-kernel file I have:

    name = "whole_kernel_tree",

    srcs = glob(["**/*"],

                exclude = [".git/**"]),

)

filegroup(

    name = "config_file",

    srcs = [".config"],

)

My BUILD file then looks like this:

load("@bazel_skylib//lib:paths.bzl", "paths")

load("@rules_foreign_cc//foreign_cc:defs.bzl", "make")

filegroup(

    name="nfnetmap_queue_src",

    srcs = [

        "nfnetmap_queue.c",

        "nfnetmap_queue_meta.h",

        "Kbuild",

        "Makefile",

    ],

)

make(

    name = "nfnetmap_queue",

    data = [

        "@kernel_source_host//:whole_kernel_tree",

        "@kernel_source_host//:config_file",

    ],

    targets = ["default"],

    env = {

        "KERNELDIR": MYSTERY_GOES_HERE

    },

    lib_source = ":nfnetmap_queue_src",

    out_binaries = ["nfnetmap_queue.ko"],

)

I'd like the mystery text to be the execpath of my copied kernel source tree.

I've come up with several variations on a theme which fail.

The closest is "$(execpath @kernel_source_host//:config_file)" which gets me the correct execpath of the config file, but not the containing directory.

paths.dirname("$(execpath @kernel_source_host//:config_file)")

seems like it should work, but I end up with complaints of "unterminated $(execpath) expression". Attempts to quote around this haven't gotten me anywhere.

"$(execpath paths.dirname(@kernel_source_host//:config_file))"

seems even less likely to work, and it ends up with invalid target name 'paths.dirname(@kernel_source_host//:config_file': target names may not contain '//' path separators

This seems like something which should be straight-forward to do, but I haven't found any good references.

-     Garrett

[Garrett Kajmowicz]

Are there any ways to generate execpath in Starlark? I couldn't find any obvious examples. I tried searching through the Bazel Java codebase for the implementation and didn't find much that was that useful (lots of noise from parameters named execPath).

-     Garrett