dnl ######################################################################
dnl Common m4sh code for compiler stuff
AC_DEFUN([NTP_COMPILER], [

AC_USE_SYSTEM_EXTENSIONS

# Ralf Wildenhues: With per-target flags we need CC_C_O
# AM_PROG_CC_C_O supersets AC_PROG_CC_C_O
AM_PROG_CC_C_O
AC_PROG_GCC_TRADITIONAL
AC_REQUIRE([AC_PROG_CC_STDC])
dnl AC_REQUIRE([AC_PROG_CC_C89])
dnl AC_REQUIRE([AC_PROG_CC_C99])

CC_NOFORMAT=
CFLAGS_NTP=
CPPFLAGS_NTP=
LDADD_NTP=
LDFLAGS_NTP=
AC_SUBST([CC_NOFORMAT])
AC_SUBST([CFLAGS_NTP])
AC_SUBST([CPPFLAGS_NTP])
AC_SUBST([LDADD_NTP])
AC_SUBST([LDFLAGS_NTP])

case "$ac_cv_prog_cc_c89" in
 no)
    AC_MSG_WARN([ANSI C89/ISO C90 is the minimum to compile NTP]
		[ version 4.2.5 and higher.])
    ;;
esac

AC_CACHE_CHECK(
    [if $CC can handle @%:@warning],
    [ntp_cv_cpp_warning],
    [AC_COMPILE_IFELSE(
	[AC_LANG_PROGRAM([[]], [[#warning foo]])],
	[ntp_cv_cpp_warning=yes],
	[ntp_cv_cpp_warning=no]
    )]
)
case "$ntp_cv_cpp_warning" in
 no)
    AC_DEFINE([NO_OPTION_NAME_WARNINGS], [1],
	[Should we avoid @%:@warning on option name collisions?])
esac

AC_CACHE_CHECK(
    [if $CC supports __attribute__((...))],
    [ntp_cv_cc_attribute],
    [AC_COMPILE_IFELSE(
	[AC_LANG_PROGRAM(
	    [[]],
	    [[void foo(void) __attribute__((__noreturn__));]]
	    )],
	[ntp_cv_cc_attribute=yes],
	[ntp_cv_cc_attribute=no]
    )]
)
case "$ntp_cv_cc_attribute" in
 yes)
    AC_DEFINE([HAVE___ATTRIBUTE__], [],
	[defined if C compiler supports __attribute__((...))])
esac
AH_VERBATIM(
    [HAVE___ATTRIBUTE___VERBATIM],
    [
	/* define away __attribute__() if unsupported */
	#ifndef HAVE___ATTRIBUTE__
	# define __attribute__(x) /* empty */
	#endif
	#define ISC_PLATFORM_NORETURN_PRE
	#define ISC_PLATFORM_NORETURN_POST __attribute__((__noreturn__))
    ]
)

case "$GCC" in
 yes)
    SAVED_CFLAGS="$CFLAGS"
    CFLAGS="$SAVED_CFLAGS -Wstrict-overflow"
    AC_CACHE_CHECK(
	[if $CC can handle -Wstrict-overflow], 
	[ntp_cv_gcc_Wstrict_overflow], 
	[AC_COMPILE_IFELSE(
	    [AC_LANG_PROGRAM([[]], [[]])],
	    [ntp_cv_gcc_Wstrict_overflow=yes],
	    [ntp_cv_gcc_Wstrict_overflow=no]
	)	]
    )
    #
    # $ntp_cv_gcc_Wstrict_overflow is tested later to add the 
    # flag to CFLAGS.
    #
    CFLAGS="$SAVED_CFLAGS -Winit-self"
    AC_CACHE_CHECK(
	[if $CC can handle -Winit-self], 
	[ntp_cv_gcc_Winit_self],
	[
	    AC_COMPILE_IFELSE(
		[AC_LANG_PROGRAM([[]], [[]])],
		[ntp_cv_gcc_Winit_self=yes],
		[ntp_cv_gcc_Winit_self=no]
	    )
	]
    )
    #
    # libopts specifically builds a string with embedded NULs.
    # This causes a bunch of distracting warnings due to -Wformat.
    # Let's see if we can figure out how to disable these.
    #
    CFLAGS="$SAVED_CFLAGS -Wno-format"
    AC_CACHE_CHECK(
	[if $CC can handle -Wno-format], 
	[ntp_cv_gcc_Wno_format],
	[
	    AC_COMPILE_IFELSE(
		[AC_LANG_PROGRAM([[]], [[]])],
		[ntp_cv_gcc_Wno_format=yes],
		[ntp_cv_gcc_Wno_format=no]
	    )
	]
    )

    case "$ntp_cv_gcc_Wno_format" in
     yes)
	CC_NOFORMAT="$CC_NOFORMAT -Wno-format"
	;;
     no)
	;;
    esac

    CFLAGS="$SAVED_CFLAGS"
    AS_UNSET([SAVED_CFLAGS])
    #
    # $ntp_cv_gcc_Winit_self is tested later to add the 
    # flag to CFLAGS_NTP.
    #
    AC_CACHE_CHECK(
	[if linker supports omitting unused code and data],
	[ntp_cv_gc_sections_runs],
	[
	    dnl  NetBSD will link but likely not run with --gc-sections
	    dnl  http://bugs.ntp.org/1844
	    dnl  http://gnats.netbsd.org/40401
	    dnl  --gc-sections causes attempt to load as linux elf, with
	    dnl  wrong syscalls in place.  Test a little gauntlet of
	    dnl  simple stdio read code checking for errors, expecting
	    dnl  enough syscall differences that the NetBSD code will
	    dnl  fail even with Linux emulation working as designed.
	    dnl  A shorter test could be refined by someone with access
	    dnl  to a NetBSD host with Linux emulation working.
	    origCFLAGS="$CFLAGS"
	    CFLAGS="$CFLAGS -Wl,--gc-sections"
	    AC_LINK_IFELSE(
		[AC_LANG_PROGRAM(
		    [[
			#include <stdlib.h>
			#include <stdio.h>
		    ]],
		    [[
			FILE *	fpC;
			char	buf[32];
			size_t	cch;
			int	read_success_once;

			fpC = fopen("conftest.c", "r");
			if (NULL == fpC)
				exit(1);
			do {
				cch = fread(buf, sizeof(buf), 1, fpC);
				read_success_once |= (0 != cch);
			} while (0 != cch);
			if (!read_success_once)
				exit(2);
			if (!feof(fpC))
				exit(3);
			if (0 != fclose(fpC))
				exit(4);

			exit(EXIT_SUCCESS);
		    ]]
		)],
		[
		    if test "X$cross_compiling" = "Xyes" || grep gc-sections conftest.err ; then
			ntp_cv_gc_sections_runs=no
		    else
			ntp_cv_gc_sections_runs=no
			./conftest >/dev/null 2>&1 && ntp_cv_gc_sections_runs=yes
		    fi
		],
		[ntp_cv_gc_sections_runs=no]
	    )
	    CFLAGS="$origCFLAGS"
	    AS_UNSET([origCFLAGS])
	]
    )
    case "$ntp_cv_gc_sections_runs" in
     yes)
	LDADD_LIBNTP="-Wl,--gc-sections"
	CFLAGS_NTP="$CFLAGS_NTP -ffunction-sections -fdata-sections"
	;;
     no)
	LDADD_LIBNTP=
	;;
    esac
    CFLAGS_NTP="$CFLAGS_NTP -Wall"
    CFLAGS_NTP="$CFLAGS_NTP -Wcast-align"
    CFLAGS_NTP="$CFLAGS_NTP -Wcast-qual"
    # CFLAGS_NTP="$CFLAGS_NTP -Wconversion"
    # CFLAGS_NTP="$CFLAGS_NTP -Werror"
    # CFLAGS_NTP="$CFLAGS_NTP -Wextra"
    # CFLAGS_NTP="$CFLAGS_NTP -Wfloat-equal"
    CFLAGS_NTP="$CFLAGS_NTP -Wmissing-prototypes"
    CFLAGS_NTP="$CFLAGS_NTP -Wpointer-arith"
    CFLAGS_NTP="$CFLAGS_NTP -Wshadow"
    # CFLAGS_NTP="$CFLAGS_NTP -Wtraditional"
    # CFLAGS_NTP="$CFLAGS_NTP -Wwrite-strings"
    case "$ntp_cv_gcc_Winit_self" in
     yes)
	CFLAGS_NTP="$CFLAGS_NTP -Winit-self"
    esac
    case "$ntp_cv_gcc_Wstrict_overflow" in
     yes)
	CFLAGS_NTP="$CFLAGS_NTP -Wstrict-overflow"
    esac
    # -W[no-]strict-prototypes might be added by NTP_OPENSSL
esac

NTP_OS_CFLAGS

AC_C_BIGENDIAN
AC_C_VOLATILE
AC_PROG_CPP

])dnl
dnl ======================================================================