WIP: autotools support for LKM

m4/ax_linuxkm.m4

@@ -0,0 +1,41 @@
+AC_DEFUN([AC_PATH_DEFAULT_KERNEL_SOURCE],
+[
+AC_MSG_CHECKING([for default kernel build root])
+if test -d /lib/modules/`uname -r`/build/.config; then
+  DEFAULT_KROOT=/lib/modules/`uname -r`/build
+  AC_MSG_RESULT([$DEFAULT_KROOT])
+elif test -r /usr/src/linux/.config; then
+  DEFAULT_KROOT=/usr/src/linux
+  AC_MSG_RESULT([$DEFAULT_KROOT])
+else
+  AC_MSG_RESULT([no default configured kernel found])
+fi
+])
+
+AC_DEFUN([AC_DEFAULT_KERNEL_ARCH],
+[
+AC_REQUIRE([AC_PROG_AWK])
+AC_MSG_CHECKING([for default kernel arch])
+if test -f ${KROOT}/.config; then
+  # "# Linux/x86 5.8.1-gentoo Kernel Configuration"
+  DEFAULT_KARCH=`$AWK '/^# Linux/\
+{split($[]2,arch_fields,"/"); print arch_fields[[2]]; exit(0);}' ${KROOT}/.config`
+fi
+if test -n "$DEFAULT_KARCH"; then
+  AC_MSG_RESULT([$DEFAULT_KARCH])
+else
+  AC_MSG_RESULT([no default configured kernel arch found])
+fi
+])
+
+AC_DEFUN([AC_DEFINE_KERNEL_KFLAGS],
+[
+    AC_MSG_CHECKING([flags for compiling objects for kernel module])
+    if test -z "${KROOT}" || test -z "${KARCH}"; then
+        AC_MSG_ERROR([Linux kernel configuration incomplete (KROOT=${KROOT}, KARCH=${KARCH}).])
+    else
+        GCC_SHORT_VERSION="$($CC -dumpversion)"
+        KFLAGS="-I${KROOT}/include -I${KROOT}/include/uapi -I${KROOT}/arch/${KARCH}/include -I${KROOT}/arch/${KARCH}/include/generated -I${KROOT}/arch/${KARCH}/include/generated/uapi -I${KROOT}/arch/${KARCH}/include/uapi -I${KROOT}/tools/include -I${KROOT}/tools/arch/${KARCH}/include -I${KROOT}/tools/include/uapi -I/usr/lib/gcc/${host_cpu}-${host_vendor}-${host_os}/${GCC_SHORT_VERSION}/include"
+        AC_MSG_RESULT([$KFLAGS])
+    fi
+])