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 <[email protected]>

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))

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