[openwrt/openwrt] build: add support for using prebuilt LLVM toolchain

[LEDE Commits]

nbd pushed a commit to openwrt/openwrt.git, branch master:
https://git.openwrt.org/9f90a89655d41ba8afcd8018d7bc8b3753beb17e

commit 9f90a89655d41ba8afcd8018d7bc8b3753beb17e
Author: Felix Fietkau <nbd at nbd.name>
AuthorDate: Thu Nov 4 20:04:44 2021 +0100

    build: add support for using prebuilt LLVM toolchain
    
    When the prebuilt llvm toolchain is unpacked into the source dir,
    it is automatically picked up and used by the build system, and eBPF
    based packages can be selected
    
    Signed-off-by: Felix Fietkau <nbd at nbd.name>
---
 include/bpf.mk      | 10 +++++++---
 toolchain/Config.in | 14 ++++++++++++++
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/include/bpf.mk b/include/bpf.mk
index 28cdf6cb32..c68ad74554 100644
--- a/include/bpf.mk
+++ b/include/bpf.mk
@@ -1,6 +1,7 @@
 BPF_DEPENDS := @HAS_BPF_TOOLCHAIN
+LLVM_VER:=
 
-ifneq ($(CONFIG_BPF_TOOLCHAIN_HOST),)
+ifneq ($(CONFIG_USE_LLVM_HOST),)
   BPF_TOOLCHAIN_HOST_PATH:=$(call qstrip,$(CONFIG_BPF_TOOLCHAIN_HOST_PATH))
   ifneq ($(BPF_TOOLCHAIN_HOST_PATH),)
     BPF_PATH:=$(BPF_TOOLCHAIN_HOST_PATH)/bin:$(PATH)
@@ -9,9 +10,12 @@ ifneq ($(CONFIG_BPF_TOOLCHAIN_HOST),)
   endif
   CLANG:=$(firstword $(shell PATH='$(BPF_PATH)' which clang clang-13 clang-12 clang-11))
   LLVM_VER:=$(subst clang,,$(notdir $(CLANG)))
-else
+endif
+ifneq ($(CONFIG_USE_LLVM_PREBUILT),)
+  CLANG:=$(TOPDIR)/llvm-bpf/bin/clang
+endif
+ifneq ($(CONFIG_USE_LLVM_BUILD),)
   CLANG:=$(STAGING_DIR_HOST)/llvm-bpf/bin/clang
-  LLVM_VER:=
 endif
 
 LLVM_PATH:=$(dir $(CLANG))
diff --git a/toolchain/Config.in b/toolchain/Config.in
index a7da2a1f73..366f5c8b48 100644
--- a/toolchain/Config.in
+++ b/toolchain/Config.in
@@ -41,11 +41,17 @@ menuconfig TARGET_OPTIONS
 	choice BPF_TOOLCHAIN
 		prompt "BPF toolchain" if DEVEL
 		default BPF_TOOLCHAIN_BUILD_LLVM if BUILDBOT
+		default BPF_TOOLCHAIN_PREBUILT if HAS_PREBUILT_LLVM_TOOLCHAIN
 		default BPF_TOOLCHAIN_NONE
 
 		config BPF_TOOLCHAIN_NONE
 			bool "None"
 
+		config BPF_TOOLCHAIN_PREBUILT
+			bool "Use prebuilt LLVM toolchain"
+			depends on HAS_PREBUILT_LLVM_TOOLCHAIN
+			select USE_LLVM_PREBUILT
+
 		config BPF_TOOLCHAIN_HOST
 			select USE_LLVM_HOST
 			bool "Use host LLVM toolchain"
@@ -298,10 +304,18 @@ config GDB_PYTHON
 config HAS_BPF_TOOLCHAIN
 	bool
 
+config HAS_PREBUILT_LLVM_TOOLCHAIN
+	def_bool $(shell, [ -f llvm-bpf/.llvm-version ] && echo y || echo n)
+
 config USE_LLVM_HOST
 	select HAS_BPF_TOOLCHAIN
 	bool
 
+config USE_LLVM_PREBUILT
+	select HAS_BPF_TOOLCHAIN
+	default y if !DEVEL && !BUILDBOT && HAS_PREBUILT_LLVM_TOOLCHAIN
+	bool
+
 config USE_LLVM_BUILD
 	default y if !DEVEL && BUILDBOT
 	select HAS_BPF_TOOLCHAIN