eclass/go-env.eclass: add helper to set compile env

This change adds a helper function to explicitly set CC, CXX, and
GOARCH, and carrying over CFLAGS, LDFLAGS and friends to CGO
equivalents, to provide a minimal sane compile environment for Go.
It enables Go builds to play nice with crossdev's wrappers for
emerge/ebuild etc. Previously, Go ebuilds emitted binaries for the host
architecture.

For example, when running on an x86_64 host:
   emerge-aarch64-cross-linux-gnu foo
will now correctly emerge Go package "foo" for aarch64 instead of
x86_64.

The eclass provides a single helper function
    go-env_set_compile_environment()
intended to be called by other Go eclasses in an early build stage.
Ebuilds may also explicitly call this function.

Signed-off-by: Thilo Fromm <thilo.alexander@gmail.com>
Signed-off-by: James Le Cuirot <chewi@gentoo.org>

1 files changed, 48 insertions, 0 deletions

diff --git a/eclass/go-env.eclass b/eclass/go-env.eclass
new file mode 100644
index 000000000000..ba4f6c3fbb59
--- /dev/null
+++ b/eclass/go-env.eclass
@@ -0,0 +1,48 @@
+# Copyright 2023 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+# @ECLASS: go-env.eclass
+# @MAINTAINER:
+# Flatcar Linux Maintainers <infra@flatcar-linux.org>
+# @AUTHOR:
+# Flatcar Linux Maintainers <infra@flatcar-linux.org>
+# @BLURB: Helper eclass for setting the Go compile environment. Required for cross-compiling.
+# @DESCRIPTION:
+# This eclass includes a helper function for setting the compile environment for Go ebuilds.
+# Intended to be called by other Go eclasses in an early build stage, e.g. src_unpack.
+
+if [[ -z ${_GO_ENV_ECLASS} ]]; then
+_GO_ENV_ECLASS=1
+
+inherit toolchain-funcs
+
+# @FUNCTION: go-env_set_compile_environment
+# @DESCRIPTION:
+# Set up basic compile environment: CC, CXX, and GOARCH.
+# Also carry over CFLAGS, LDFLAGS and friends.
+# Required for cross-compiling with crossdev.
+# If not set, host defaults will be used and the resulting binaries are host arch.
+# (e.g. "emerge-aarch64-cross-linux-gnu foo" run on x86_64 will emerge "foo" for x86_64
+#  instead of aarch64)
+go-env_set_compile_environment() {
+	local arch="$(tc-arch)"
+	case "${arch}" in
+		x86)	GOARCH="386" ;;
+		x64-*)	GOARCH="amd64" ;;
+		ppc64)	if [[ "$(tc-endian)" == "big" ]] ; then
+					GOARCH="ppc64"
+				else
+					GOARCH="ppc64le"
+				fi ;;
+			*)	GOARCH="${arch}" ;;
+	esac
+
+	tc-export CC CXX
+	export GOARCH
+	export CGO_CFLAGS="${CGO_CFLAGS:-$CFLAGS}"
+	export CGO_CPPFLAGS="${CGO_CPPFLAGS:-$CPPFLAGS}"
+	export CGO_CXXFLAGS="${CGO_CXXFLAGS:-$CXXFLAGS}"
+	export CGO_LDFLAGS="${CGO_LDFLAGS:-$LDFLAGS}"
+}
+
+fi