Implement cross-compilation based on sysroot using Clang (#6)

* Implement cross-compilation based on sysroot using Clang

* Propagate computed environment variable into Dockerized invocation

* Add documentation

Dockerfile

@@ -2,14 +2,9 @@ FROM debian:testing
 
 WORKDIR /agent
 
-# cross_debian_arch: amd64 or arm64
-# cross_pkg_arch: x86-64 or aarch64
-RUN cross_debian_arch=$(uname -m | sed -e 's/aarch64/amd64/'  -e 's/x86_64/arm64/'); \
-    cross_pkg_arch=$(uname -m | sed -e 's/aarch64/x86-64/' -e 's/x86_64/aarch64/'); \
-    apt-get update -y && \
+RUN apt-get update -y && \
     apt-get dist-upgrade -y && \
-    apt-get install -y wget make git clang-16 unzip libc6-dev g++ gcc pkgconf \
-        gcc-${cross_pkg_arch}-linux-gnu libc6-${cross_debian_arch}-cross && \
+    apt-get install -y clang-16 git lld-16 make pkgconf unzip wget && \
     apt-get clean autoclean && \
     apt-get autoremove --yes
 

Makefile

@@ -16,21 +16,24 @@ endif
 # Valid values are: amd64, arm64.
 TARGET_ARCH ?= $(NATIVE_ARCH)
 
-ifeq ($(NATIVE_ARCH),$(TARGET_ARCH))
-ARCH_PREFIX :=
-else ifeq ($(TARGET_ARCH),arm64)
-ARCH_PREFIX := aarch64-linux-gnu-
+ifeq ($(TARGET_ARCH),arm64)
+COMPILER_TARGET_ARCH := aarch64
 else ifeq ($(TARGET_ARCH),amd64)
-ARCH_PREFIX := x86_64-linux-gnu-
+COMPILER_TARGET_ARCH := x86_64
 else
 $(error Unsupported architecture: $(TARGET_ARCH))
 endif
 
-export TARGET_ARCH
+COMPILER_TARGET ?= $(COMPILER_TARGET_ARCH)-redhat-linux
+SYSROOT_PATH ?= /
+
+export CC = clang-16
+export COMPILER_TARGET
+export CGO_CFLAGS = --sysroot=/usr/sysroot --target=$(COMPILER_TARGET)
 export CGO_ENABLED = 1
+export CGO_LDFLAGS = -fuse-ld=lld --sysroot=/usr/sysroot
 export GOARCH = $(TARGET_ARCH)
-export CC = $(ARCH_PREFIX)clang-16
-export OBJCOPY = $(ARCH_PREFIX)objcopy
+export TARGET_ARCH
 
 BRANCH = $(shell git rev-parse --abbrev-ref HEAD | tr -d '-' | tr '[:upper:]' '[:lower:]')
 COMMIT_SHORT_SHA = $(shell git rev-parse --short=8 HEAD)
@@ -41,7 +44,8 @@ REVISION ?= $(BRANCH)-$(COMMIT_SHORT_SHA)
 
 LDFLAGS := -X go.opentelemetry.io/ebpf-profiler/vc.version=$(VERSION) \
 	-X go.opentelemetry.io/ebpf-profiler/vc.revision=$(REVISION) \
-	-X go.opentelemetry.io/ebpf-profiler/vc.buildTimestamp=$(BUILD_TIMESTAMP)
+	-X go.opentelemetry.io/ebpf-profiler/vc.buildTimestamp=$(BUILD_TIMESTAMP) \
+	\"-extldflags=$(CGO_CFLAGS)\"
 
 GO_TAGS := osusergo,netgo
 EBPF_FLAGS := 
@@ -118,12 +122,12 @@ docker-image:
 	docker build -t profiling-agent -f Dockerfile .
 
 agent:
-	docker run -v "$$PWD":/agent -it --rm --user $(shell id -u):$(shell id -g) profiling-agent \
-	   "make TARGET_ARCH=$(TARGET_ARCH) VERSION=$(VERSION) REVISION=$(REVISION) BUILD_TIMESTAMP=$(BUILD_TIMESTAMP)"
+	docker run -v "$$PWD":/agent -v $(SYSROOT_PATH):/usr/sysroot -it --rm --user $(shell id -u):$(shell id -g) profiling-agent \
+	   "make COMPILER_TARGET=$(COMPILER_TARGET) TARGET_ARCH=$(TARGET_ARCH) VERSION=$(VERSION) REVISION=$(REVISION) BUILD_TIMESTAMP=$(BUILD_TIMESTAMP)"
 
 debug-agent:
-	docker run -v "$$PWD":/agent -it --rm --user $(shell id -u):$(shell id -g) profiling-agent \
-	   "make TARGET_ARCH=$(TARGET_ARCH) VERSION=$(VERSION) REVISION=$(REVISION) BUILD_TIMESTAMP=$(BUILD_TIMESTAMP) debug"
+	docker run -v "$$PWD":/agent -v $(SYSROOT_PATH):/usr/sysroot -it --rm --user $(shell id -u):$(shell id -g) profiling-agent \
+	   "make COMPILER_TARGET=$(COMPILER_TARGET) TARGET_ARCH=$(TARGET_ARCH) VERSION=$(VERSION) REVISION=$(REVISION) BUILD_TIMESTAMP=$(BUILD_TIMESTAMP) debug"
 
 legal:
 	@go install github.com/google/go-licenses@latest

README.md

@@ -42,15 +42,17 @@ The agent can be built with the provided make targets. Docker is required for co
      ```sh
      make docker-image
      ```
-  2. Build the agent for your current machine's architecture:
+  2. Build the agent for your current machine's architecture with your current environment serving as sysroot:
      ```sh
      make agent
      ```
      Or `make debug-agent` for debug build.
-  3. To cross-complie for a different architecture (e.g. arm64):
+  3. To cross-compile for a different architecture (e.g. arm64):
      ```sh
-     make agent TARGET_ARCH=arm64
+     SYSROOT_PATH=/path/to/your/desired/sysroot TARGET_ARCH=arm64 make agent
      ```
+     Where `SYSROOT_PATH` is directed at a valid sysroot for the specified `TARGET_ARCH` as defined [here](https://clang.llvm.org/docs/CrossCompilation.html).
+
 The resulting binary will be named <ebpf-profiler> in the current directory.
 
 ## Other OSes

support/ebpf/Makefile

@@ -23,17 +23,12 @@ BUILD_TYPE ?= release
 
 TRACER_NAME ?= tracer.ebpf.$(BUILD_TYPE).$(TARGET_ARCH)
 
-ifeq ($(TARGET_ARCH),arm64)
-TARGET_FLAGS = -target aarch64-linux-gnu
-else
-TARGET_FLAGS = -target x86_64-linux-gnu
-endif
-
+CFLAGS = $(CGO_CFLAGS)
 ifeq ($(BUILD_TYPE),debug)
-	TARGET_FLAGS+=$(DEBUG_FLAGS)
+	CFLAGS+=$(DEBUG_FLAGS)
 endif
 
-FLAGS=$(TARGET_FLAGS) \
+FLAGS=$(CFLAGS) \
 	-fno-jump-tables \
 	-nostdlib \
 	-nostdinc \