Makefile.inc: Make Go variables cross-compiler friendly

GOARCH needs to reflect the target architecture. GOROOT needs to point
at GOROOT that is compatible with the host.

Signed-off-by: David Hendricks <david.hendricks@gmail.com>

Author: dhendrix

Makefile.inc

@@ -72,7 +72,7 @@ INITRAMFS_BUILD_DIR := $(PLATFORM_BUILD_DIR)/initramfs
 INITRAMFS_DEPS_FLAG := $(PLATFORM_BUILD_DIR)/.initramfs-deps
 INITRAMFS_PATCH_FLAG := $(PLATFORM_BUILD_DIR)/.initramfs-patch
 ifndef INITRAMFS_OUT
-INITRAMFS_OUT := $(INITRAMFS_BUILD_DIR)/initramfs_linuxboot.$(ARCH).cpio
+INITRAMFS_OUT := $(INITRAMFS_BUILD_DIR)/initramfs_linuxboot.$(GOARCH).cpio
 endif
 # By default, build initramfs but a prebuilt one can be provided via INITRAMFS_IN.
 INITRAMFS_IN ?= $(INITRAMFS_OUT)
@@ -102,6 +102,31 @@ ifdef COREBOOT_BLOBS_DIR
 COREBOOT_BLOBS_DIR := $(realpath $(COREBOOT_BLOBS_DIR))
 endif
 
+# FIXME: Go needs to be run on the host architecture (GOARCH is used for cross-
+# compiling Go programs). However, the target platform's config will likely want
+# to use a Go tarball for that target architecture. For now, override this with
+# whatever the host has installed. THIS IS A GROSS HACK.
+#
+# We might change the json schema to specify only Go version, but not point at
+# a particular tarball (which includes architecture in the name). This would
+# also require changing the download verification scheme to something like GPG
+# signature instead of sha255sum, since the hash will obviously be different
+# among tarballs for different architectures.
+#
+# FIXME #2: It's not clear if we want to always use the coreboot toolchain when
+# cross compiling Linux. It's certainly an easy approach, though.
+#
+# FIXME #3: Some distros add the version number of the tool as a suffix, for
+# example "x86_64-linux-gnu-gcc-10".
+ifeq ($(CROSS_COMPILING), 1)
+INITRAMFS_BUILD_GOROOT ?= /usr/local/go
+else
+# FIXME: Also need to fix behavior when we're not cross-compilng, but system's
+# go version doesn't match the version we're using to build the initramfs...
+#INITRAMFS_BUILD_GOROOT ?= $(INITRAMFS_BUILD_DIR)/go
+INITRAMFS_BUILD_GOROOT ?= /usr/local/go
+endif
+
 UROOT_BOOT_CMDS := fbnetboot localboot systemboot
 UROOT_EXP_CMDS := cbmem dmidecode modprobe ipmidump
 UROOT_BASE_CMDS ?= \
@@ -256,10 +281,11 @@ initramfs: $(INITRAMFS_OUT)
 # Initramfs build target.
 $(INITRAMFS_OUT): $(INITRAMFS_DEPS_FLAG) $(INITRAMFS_PATCH_FLAG)
 	GO111MODULE=off \
-	GOROOT=$(INITRAMFS_BUILD_DIR)/go \
+	GOARCH=$(GOARCH) \
+	GOROOT=$(INITRAMFS_BUILD_GOROOT) \
 	GOCACHE=$(INITRAMFS_BUILD_DIR)/go/.cache \
 	GOPATH=$(INITRAMFS_BUILD_DIR)/gopath:$(UROOT_ADDITIONAL_GOPATH) \
-	  $(INITRAMFS_BUILD_DIR)/go/bin/go run github.com/u-root/u-root \
+	  $(GOROOT)/bin/go run github.com/u-root/u-root \
 	    -build=bb -o $@ -uinitcmd=$(UINIT_CMD) \
 	    $(addprefix -files=,$(BASE_FILES) $(UROOT_ADDITIONAL_FILES)) \
 	    $(UROOT_ADDITIONAL_CMDS) \

examples/qemu/Makefile

@@ -5,11 +5,16 @@
 # LICENSE file in the root directory of this source tree.
 
 ARCH ?= $(shell uname -m)
+ifneq ($(ARCH), $(shell uname -m))
+CROSS_COMPILING := 1
+else
+CROSS_COMPILING := 0
+endif
 
 ifeq ($(ARCH), x86_64)
-ARCH = amd64
 LINUX_ARCH := $(ARCH)
 LINUX_IMAGE_RELATIVE_PATH := arch/x86/boot/bzImage
+GOARCH := amd64
 PLATFORM := qemu-amd64
 QEMU_SYSTEM := qemu-system-$(ARCH)
 endif