[PATCH 36/40] bootlinux: Add an option to build with clang instead of gcc

[Luis Chamberlain <mcgrof@kernel.org>]

From: Chuck Lever <chuck.lever@oracle.com>

Currently, gcc does not implement a Rust front-end. As the kernel
acquires Rust source code, the clang tool chain must be used to
build it.

To enable building test kernels with clang instead of gcc, add a
kdevops Kconfig option to install dependences and set the build
options to use clang.

See: Documentation/kbuild/llvm.rst

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 .../roles/bootlinux/tasks/build/builder.yml   | 36 +++++++++++++++++++
 .../tasks/install-deps/redhat/main.yml        | 16 +++++++++
 workflows/linux/Kconfig                       | 20 +++++++++++
 3 files changed, 72 insertions(+)

diff --git a/playbooks/roles/bootlinux/tasks/build/builder.yml b/playbooks/roles/bootlinux/tasks/build/builder.yml
index c8363b8e..c4c4b950 100644
--- a/playbooks/roles/bootlinux/tasks/build/builder.yml
+++ b/playbooks/roles/bootlinux/tasks/build/builder.yml
@@ -110,12 +110,35 @@
   community.general.make:
     chdir: "{{ target_linux_dir_path }}"
     target: "olddefconfig"
+  when:
+    - bootlinux_compiler_gcc|bool
 
 - name: Build {{ target_linux_tree }}
   community.general.make:
     chdir: "{{ target_linux_dir_path }}"
     jobs: "{{ ansible_processor_nproc }}"
     target: "all"
+  when:
+    - bootlinux_compiler_gcc|bool
+
+- name: Configure kernel {{ target_linux_tree }}
+  community.general.make:
+    chdir: "{{ target_linux_dir_path }}"
+    params:
+      LLVM: 1
+    target: "olddefconfig"
+  when:
+    - bootlinux_compiler_clang|bool
+
+- name: Build {{ target_linux_tree }}
+  community.general.make:
+    chdir: "{{ target_linux_dir_path }}"
+    jobs: "{{ ansible_processor_nproc }}"
+    params:
+      LLVM: 1
+    target: "all"
+  when:
+    - bootlinux_compiler_clang|bool
 
 - name: Remove the old artifacts directory on the control host
   delegate_to: localhost
@@ -192,6 +215,19 @@
         target: "binrpm-pkg"
         params:
           RPMOPTS: '--without devel'
+      when:
+        - bootlinux_compiler_gcc|bool
+
+    - name: Make the binrpm-pkg target
+      community.general.make:
+        chdir: "{{ target_linux_dir_path }}"
+        jobs: "{{ ansible_processor_nproc }}"
+        target: "binrpm-pkg"
+        params:
+          RPMOPTS: '--without devel'
+          LLVM: 1
+      when:
+        - bootlinux_compiler_clang|bool
 
     - name: Find the build artifacts
       ansible.builtin.find:
diff --git a/playbooks/roles/bootlinux/tasks/install-deps/redhat/main.yml b/playbooks/roles/bootlinux/tasks/install-deps/redhat/main.yml
index 0f966d67..dc4a5433 100644
--- a/playbooks/roles/bootlinux/tasks/install-deps/redhat/main.yml
+++ b/playbooks/roles/bootlinux/tasks/install-deps/redhat/main.yml
@@ -68,6 +68,22 @@
       - btrfs-progs
   when: ansible_distribution == 'Fedora'
 
+- name: Install clang
+  become: true
+  ansible.builtin.dnf:
+    name:
+      - clang
+      - lld
+      - llvm
+    state: present
+    update_cache: true
+  retries: 3
+  delay: 5
+  register: clang_result
+  until: clang_result is succeeded
+  when:
+    - bootlinux_compiler_clang|bool
+
 - name: Install rpmbuild
   become: true
   become_method: ansible.builtin.sudo
diff --git a/workflows/linux/Kconfig b/workflows/linux/Kconfig
index 31f57017..06742f3e 100644
--- a/workflows/linux/Kconfig
+++ b/workflows/linux/Kconfig
@@ -151,6 +151,26 @@ endmenu
 
 endif # BOOTLINUX_9P
 
+choice
+	prompt "Compiler to use to build the kernel"
+	default BOOTLINUX_COMPILER_GCC
+	help
+	  Choose which toolchain to use to build the kernel.
+
+config BOOTLINUX_COMPILER_GCC
+	bool "gcc"
+	output yaml
+	help
+	  Use the gcc compiler toolchain to build the Linux kernel.
+
+config BOOTLINUX_COMPILER_CLANG
+	bool "clang"
+	output yaml
+	help
+	  Use the clang compiler toolchain to build the Linux kernel.
+
+endchoice
+
 choice
 	prompt "Type of development version of Linux to use"
 	default BOOTLINUX_LINUS if !BOOTLINUX_TREE_SET_BY_CLI && !BOOTLINUX_TREE_REF_SET_BY_CLI
-- 
2.47.2