[libvirt] [PATCH v2 1/6] build: introduce logic for using golang in libvirt

[Daniel P. Berrangé]

This decides on requiring Golang >= 1.11, since that introduces
the new standard concept of "Go modules":

  https://blog.golang.org/using-go-modules

Previously such a concept was dealt with by any number of
external 3rd party. These didn't seemlessly integrate into
the go toolchain in the way modules do.

The particularly attractive benefits of Go modules are

 - You are /not/ forced to use a particular directory
   hierarchy that matches your package import name.

 - Independent of any global $GOPATH which may or may
   not be set in your user sesion.

 - External dependencies do not need vendoring (copying)
   into the libvirt source tree. The toolchain downloads
   (with local caching) as needed, or can be pointed to
   a local OS distro provided copy

Right now Fedora's Go packaging does not support Go modules,
and obviously doesn't dynamically download packages during
build. Thus in the RPM we need to turn off the normal Go
module support and point it at the local copies of deps,
provided by RPMs.

This is still static linking, but without the deps being
bundled in libvirt's src.rpm.

Fedora also does not yet have the %gobuildflags macro
defined, so in the short term we must define the desired
Go build flags to ensure debuginfo RPMs work.

Signed-off-by: Daniel P. Berrangé <berrange at redhat.com>
---
 configure.ac      |  1 +
 libvirt.spec.in   | 19 ++++++++++++++++++-
 m4/virt-golang.m4 | 46 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 65 insertions(+), 1 deletion(-)
 create mode 100644 m4/virt-golang.m4

diff --git a/configure.ac b/configure.ac
index af8cbcdfd8..b835a10698 100644
--- a/configure.ac
+++ b/configure.ac
@@ -511,6 +511,7 @@ LIBVIRT_ARG_TLS_PRIORITY
 LIBVIRT_ARG_SYSCTL_CONFIG
 
 
+LIBVIRT_CHECK_GOLANG
 LIBVIRT_CHECK_DEBUG
 LIBVIRT_CHECK_DTRACE
 LIBVIRT_CHECK_NUMAD
diff --git a/libvirt.spec.in b/libvirt.spec.in
index 7f5183f341..1c74dbb252 100644
--- a/libvirt.spec.in
+++ b/libvirt.spec.in
@@ -401,6 +401,8 @@ BuildRequires: libtirpc-devel
 BuildRequires: firewalld-filesystem
 %endif
 
+BuildRequires: golang >= 1.11
+
 Provides: bundled(gnulib)
 
 %description
@@ -1161,6 +1163,21 @@ export SOURCE_DATE_EPOCH=$(stat --printf='%Y' %{_specdir}/%{name}.spec)
  autoreconf -if
 %endif
 
+# We're building without go modules enabled, so
+# must make a local Go root with the old style
+# dir naming scheme/hierarchy
+mkdir -p gocode/src/libvirt.org
+
+export GO111MODULE=off
+export GOPATH=/usr/share/gocode:`pwd`/gocode
+
+%if 0%{?fedora} >= 32
+GOBUILDFLAGS="%gobuildflags"
+%else
+GOBUILDFLAGS="-buildmode pie -compiler gc -tags=\"rpm_crashtraceback ${BUILDTAGS:-}\" -ldflags \"${LDFLAGS:-} -B 0x$(head -c20 /dev/urandom|od -An -tx1|tr -d ' \n') -extldflags '-Wl,-z,relro -Wl,--as-needed  -Wl,-z,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld '\" -a -v -x"
+%endif
+export GOBUILDFLAGS
+
 rm -f po/stamp-po
 %configure --with-runstatedir=%{_rundir} \
            %{?arg_qemu} \
@@ -1224,7 +1241,7 @@ rm -f po/stamp-po
            --enable-expensive-tests \
            --with-init-script=systemd \
            %{?arg_login_shell}
-make %{?_smp_mflags} V=1
+make %{?_smp_mflags} V=1 GOBUILDFLAGS="$GOBUILDFLAGS"
 
 %install
 rm -fr %{buildroot}
diff --git a/m4/virt-golang.m4 b/m4/virt-golang.m4
new file mode 100644
index 0000000000..2e39bdac7d
--- /dev/null
+++ b/m4/virt-golang.m4
@@ -0,0 +1,46 @@
+dnl Golang checks
+dnl
+dnl Copyright (C) 2019 Red Hat, Inc.
+dnl
+dnl This library is free software; you can redistribute it and/or
+dnl modify it under the terms of the GNU Lesser General Public
+dnl License as published by the Free Software Foundation; either
+dnl version 2.1 of the License, or (at your option) any later version.
+dnl
+dnl This library is distributed in the hope that it will be useful,
+dnl but WITHOUT ANY WARRANTY; without even the implied warranty of
+dnl MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+dnl Lesser General Public License for more details.
+dnl
+dnl You should have received a copy of the GNU Lesser General Public
+dnl License along with this library.  If not, see
+dnl <http://www.gnu.org/licenses/>.
+dnl
+
+AC_DEFUN([LIBVIRT_CHECK_GOLANG], [
+  AC_PATH_PROGS([GO], [go], [no])
+  if test "x$ac_cv_path_GO" != "xno"
+  then
+    with_go=yes
+  else
+    with_go=no
+  fi
+  AM_CONDITIONAL([HAVE_GOLANG], [test "$with_go" != "no"])
+
+  if test "$with_go" != "no"
+  then
+    GOVERSION=`$ac_cv_path_GO version | awk '{print \$ 3}' | sed -e 's/go//' -e 's/rc.*//'`
+    GOMAJOR=`echo $GOVERSION | awk -F . '{print \$ 1}'`
+    GOMINOR=`echo $GOVERSION | awk -F . '{print \$ 2}'`
+
+    dnl We want to use go modules which first arrived in 1.11
+    AC_MSG_CHECKING([for Go version >= 1.11])
+    if test "$GOMAJOR" != "1" || test "$GOMINOR" -lt "11"
+    then
+      with_go=no
+      AC_MSG_RESULT([no])
+    else
+      AC_MSG_RESULT([yes])
+    fi
+  fi
+])
-- 
2.21.0