Make the CFLAGS more robust.

This patch introduces a shell script to figure out the proper definitions
for the HAVE_CLOCK_ADJTIME and HAVE_ONESTEP_SYNC macros, as well as the
include path. The intent is to "do the right thing" for three different
user scenarios, namely cross compiling, compiling against a custom kernel,
and using a plain old disto kernel.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>

incdefs.sh

@@ -0,0 +1,71 @@
+#!/bin/sh
+#
+# Discover the CFLAGS to use during compilation.
+#
+# Copyright (C) 2013 Richard Cochran <richardcochran@gmail.com>
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License along
+# with this program; if not, write to the Free Software Foundation, Inc.,
+# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+#
+# Look for the clock_adjtime functional prototype in the C library.
+#
+user_flags()
+{
+	dirs=$(echo "" | ${CROSS_COMPILE}cpp -Wp,-v 2>&1 >/dev/null | grep ^" /")
+	for d in $dirs; do
+		files=$(find $d -type f -name time.h)
+		for f in $files; do
+			if grep -q clock_adjtime $f; then
+				printf " -D_GNU_SOURCE -DHAVE_CLOCK_ADJTIME"
+				return
+			fi
+		done
+	done
+}
+
+#
+# Find the most appropriate kernel header for the SIOCSHWTSTAMP ioctl.
+#
+# 1. custom kernel or cross build using KBUILD_OUTPUT
+# 2. sanitized headers installed under /lib/modules/`uname -r`/build
+# 3. normal build using standard system headers
+#
+kernel_flags()
+{
+	prefix=""
+	tstamp=/usr/include/linux/net_tstamp.h
+
+	if [ "x$KBUILD_OUTPUT" != "x" ]; then
+		# With KBUILD_OUTPUT set, we are building against
+		# either a custom kernel or a cross compiled kernel.
+		build=${KBUILD_OUTPUT}
+	else
+		# If the currently running kernel is a custom build
+		# with the headers installed, then we should use them.
+		build=/lib/modules/`uname -r`/build
+	fi
+
+	if [ -f ${build}${tstamp} ]; then
+		prefix=${build}
+		printf " -I%s/usr/include" $prefix
+	fi
+
+	if grep -q HWTSTAMP_TX_ONESTEP_SYNC ${prefix}${tstamp}; then
+		printf " -DHAVE_ONESTEP_SYNC"
+	fi
+}
+
+flags="$(user_flags)$(kernel_flags)"
+echo "$flags"

makefile

@@ -15,21 +15,12 @@
 # with this program; if not, write to the Free Software Foundation, Inc.,
 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 
-KBUILD_OUTPUT ?= /lib/modules/$(shell uname -r)/build
+KBUILD_OUTPUT =
-
-FEAT_CFLAGS :=
-ifneq ($(shell grep --no-messages clock_adjtime /usr/include/bits/time.h),)
-FEAT_CFLAGS += -D_GNU_SOURCE -DHAVE_CLOCK_ADJTIME
-endif
-ifneq ($(shell grep --no-messages HWTSTAMP_TX_ONESTEP_SYNC $(KBUILD_OUTPUT)/usr/include/linux/net_tstamp.h),)
-FEAT_CFLAGS += -DHAVE_ONESTEP_SYNC
-endif
 
 DEBUG	=
 CC	= $(CROSS_COMPILE)gcc
-INC	= -I$(KBUILD_OUTPUT)/usr/include
 VER     = -DVER=$(version)
-CFLAGS	= -Wall $(VER) $(INC) $(DEBUG) $(FEAT_CFLAGS) $(EXTRA_CFLAGS)
+CFLAGS	= -Wall $(VER) $(incdefs) $(DEBUG) $(EXTRA_CFLAGS)
 LDLIBS	= -lm -lrt $(EXTRA_LDFLAGS)
 PRG	= ptp4l pmc phc2sys hwstamp_ctl
 OBJ     = bmc.o clock.o clockadj.o config.o fault.o fsm.o ptp4l.o mave.o \
@@ -40,6 +31,7 @@ OBJECTS	= $(OBJ) hwstamp_ctl.o phc2sys.o pmc.o pmc_common.o sysoff.o
 SRC	= $(OBJECTS:.o=.c)
 DEPEND	= $(OBJECTS:.o=.d)
 srcdir	:= $(dir $(lastword $(MAKEFILE_LIST)))
+incdefs := $(shell $(srcdir)/incdefs.sh)
 version := $(shell $(srcdir)/version.sh $(srcdir))
 VPATH	= $(srcdir)