Makefile & Dockerfile: add multi arch build for arm64

Add multi arch cross compilation in the Dockerfile and multi arch
capabilities in the Makefile.

Signed-off-by: Mahe Tardy <[email protected]>

Author: mtardy

Dockerfile

@@ -1,7 +1,8 @@
-FROM golang:1.22.0@sha256:7b297d9abee021bab9046e492506b3c2da8a3722cbf301653186545ecc1e00bb as gobuilder
+FROM --platform=$BUILDPLATFORM golang:1.22.0@sha256:7b297d9abee021bab9046e492506b3c2da8a3722cbf301653186545ecc1e00bb as gobuilder
 WORKDIR /src/little-vm-helper
 COPY . .
-RUN make little-vm-helper
+ARG TARGETARCH
+RUN TARGET_ARCH=$TARGETARCH make little-vm-helper
 
 FROM busybox@sha256:6d9ac9237a84afe1516540f40a0fafdc86859b2141954b4d643af7066d598b74
 COPY --from=gobuilder /src/little-vm-helper/lvh /usr/bin/lvh

Makefile

@@ -8,6 +8,14 @@ GO_BUILD_LDFLAGS =
 GO_BUILD_LDFLAGS += -X 'github.com/cilium/little-vm-helper/pkg/version.Version=$(VERSION)'
 GO_BUILD_FLAGS += -ldflags "$(GO_BUILD_LDFLAGS)"
 
+UNAME_M := $(shell uname -m)
+ifeq ($(UNAME_M),x86_64)
+	TARGET_ARCH ?= amd64
+else ifeq ($(UNAME_M),aarch64)
+	TARGET_ARCH ?= arm64
+else
+	TARGET_ARCH ?= amd64
+endif
 
 all: tests little-vm-helper
 
@@ -16,15 +24,15 @@ tests:
 	$(GO) test -cover ./...
 
 little-vm-helper: FORCE
-	CGO_ENABLED=0 $(GO) build $(GO_BUILD_FLAGS) ./cmd/lvh
+	GOARCH=${TARGET_ARCH} CGO_ENABLED=0 $(GO) build $(GO_BUILD_FLAGS) ./cmd/lvh
 
 .PHONY: image
 image:
-	$(DOCKER) build -f Dockerfile -t $(OCIREPO) .
+	$(DOCKER) build -f Dockerfile --platform=linux/${TARGET_ARCH} -t $(OCIREPO) .
 
 .PHONY: install
 install:
-	CGO_ENABLED=0 $(GO) install ./cmd/lvh
+	GOARCH=${TARGET_ARCH} CGO_ENABLED=0 $(GO) install ./cmd/lvh
 
 clean:
 	rm -f lvh