virt-compile-warnings.m4

dnl
dnl Enable all known GCC compiler warnings, except for those
dnl we can't yet cope with
dnl
AC_DEFUN([LIBVIRT_COMPILE_WARNINGS],[
    dnl ******************************
    dnl More compiler warnings
    dnl ******************************

    AC_ARG_ENABLE([werror],
                  AS_HELP_STRING([--enable-werror], [Use -Werror (if supported)]),
                  [set_werror="$enableval"],
                  [if test -d $srcdir/.git; then
                     is_git_version=true
                     set_werror=yes
                   else
                     set_werror=no
                   fi])

    # List of warnings that are not relevant / wanted

    # Don't care about C++ compiler compat
    dontwarn="$dontwarn -Wc++-compat"
    dontwarn="$dontwarn -Wabi"
    dontwarn="$dontwarn -Wdeprecated"
    # Don't care about ancient C standard compat
    dontwarn="$dontwarn -Wtraditional"
    # Don't care about ancient C standard compat
    dontwarn="$dontwarn -Wtraditional-conversion"
    # Ignore warnings in /usr/include
    dontwarn="$dontwarn -Wsystem-headers"
    # Happy for compiler to add struct padding
    dontwarn="$dontwarn -Wpadded"
    # GCC very confused with -O2
    dontwarn="$dontwarn -Wunreachable-code"
    # Too many to deal with
    dontwarn="$dontwarn -Wconversion"
    # Too many to deal with
    dontwarn="$dontwarn -Wsign-conversion"
    # GNULIB gettext.h violates
    dontwarn="$dontwarn -Wvla"
    # Many GNULIB header violations
    dontwarn="$dontwarn -Wundef"
    # Need to allow bad cast for execve()
    dontwarn="$dontwarn -Wcast-qual"
    # We need to use long long in many places
    dontwarn="$dontwarn -Wlong-long"
    # We allow manual list of all enum cases without default:
    dontwarn="$dontwarn -Wswitch-default"
    # We allow optional default: instead of listing all enum values
    dontwarn="$dontwarn -Wswitch-enum"
    # Not a problem since we don't use -fstrict-overflow
    dontwarn="$dontwarn -Wstrict-overflow"
    # Not a problem since we don't use -funsafe-loop-optimizations
    dontwarn="$dontwarn -Wunsafe-loop-optimizations"
    # Things like virAsprintf mean we can't use this
    dontwarn="$dontwarn -Wformat-nonliteral"
    # Gnulib's stat-time.h violates this
    dontwarn="$dontwarn -Waggregate-return"
    # gcc 4.4.6 complains this is C++ only; gcc 4.7.0 implies this from -Wall
    dontwarn="$dontwarn -Wenum-compare"

    # gcc 4.2 treats attribute(format) as an implicit attribute(nonnull),
    # which triggers spurious warnings for our usage
    AC_CACHE_CHECK([whether the C compiler's -Wformat allows NULL strings],
      [lv_cv_gcc_wformat_null_works], [
      save_CFLAGS=$CFLAGS
      CFLAGS='-Wunknown-pragmas -Werror -Wformat'
      AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
        #include <stddef.h>
        static __attribute__ ((__format__ (__printf__, 1, 2))) int
        foo (const char *fmt, ...) { return !fmt; }
      ]], [[
        return foo(NULL);
      ]])],
      [lv_cv_gcc_wformat_null_works=yes],
      [lv_cv_gcc_wformat_null_works=no])
      CFLAGS=$save_CFLAGS])

    # Gnulib uses '#pragma GCC diagnostic push' to silence some
    # warnings, but older gcc doesn't support this.
    AC_CACHE_CHECK([whether pragma GCC diagnostic push works],
      [lv_cv_gcc_pragma_push_works], [
      save_CFLAGS=$CFLAGS
      CFLAGS='-Wunknown-pragmas -Werror'
      AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
        #pragma GCC diagnostic push
        #pragma GCC diagnostic pop
      ]])],
      [lv_cv_gcc_pragma_push_works=yes],
      [lv_cv_gcc_pragma_push_works=no])
      CFLAGS=$save_CFLAGS])
    if test $lv_cv_gcc_pragma_push_works = no; then
      dontwarn="$dontwarn -Wmissing-prototypes"
      dontwarn="$dontwarn -Wmissing-declarations"
      dontwarn="$dontwarn -Wcast-align"
    else
      AC_DEFINE_UNQUOTED([WORKING_PRAGMA_PUSH], 1,
       [Define to 1 if gcc supports pragma push/pop])
    fi

    dnl Check whether strchr(s, char variable) causes a bogus compile
    dnl warning, which is the case with GCC < 4.6 on some glibc
    AC_CACHE_CHECK([whether the C compiler's -Wlogical-op gives bogus warnings],
      [lv_cv_gcc_wlogical_op_broken], [
      save_CFLAGS="$CFLAGS"
      CFLAGS="-O2 -Wlogical-op -Werror"
      AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
        #include <string.h>
        ]], [[
        const char *haystack;
        char needle;
        return strchr(haystack, needle) == haystack;]])],
        [lv_cv_gcc_wlogical_op_broken=no],
        [lv_cv_gcc_wlogical_op_broken=yes])
      CFLAGS="$save_CFLAGS"])

    # We might fundamentally need some of these disabled forever, but
    # ideally we'd turn many of them on
    dontwarn="$dontwarn -Wfloat-equal"
    dontwarn="$dontwarn -Wdeclaration-after-statement"
    dontwarn="$dontwarn -Wpacked"
    dontwarn="$dontwarn -Wunused-macros"
    dontwarn="$dontwarn -Woverlength-strings"
    dontwarn="$dontwarn -Wstack-protector"

    # Get all possible GCC warnings
    gl_MANYWARN_ALL_GCC([maybewarn])

    # Remove the ones we don't want, blacklisted earlier
    gl_MANYWARN_COMPLEMENT([wantwarn], [$maybewarn], [$dontwarn])

    # GNULIB uses '-W' (aka -Wextra) which includes a bunch of stuff.
    # Unfortunately, this means you can't simply use '-Wsign-compare'
    # with gl_MANYWARN_COMPLEMENT
    # So we have -W enabled, and then have to explicitly turn off...
    wantwarn="$wantwarn -Wno-sign-compare"

    # GNULIB expects this to be part of -Wc++-compat, but we turn
    # that one off, so we need to manually enable this again
    wantwarn="$wantwarn -Wjump-misses-init"

    # GNULIB turns on -Wformat=2 which implies -Wformat-nonliteral,
    # so we need to manually re-exclude it.  Also, older gcc 4.2
    # added an implied ATTRIBUTE_NONNULL on any parameter marked
    # ATTRIBUTE_FMT_PRINT, which causes -Wformat failure on our
    # intentional use of virReportError(code, NULL).
    wantwarn="$wantwarn -Wno-format-nonliteral"
    if test $lv_cv_gcc_wformat_null_works = no; then
      wantwarn="$wantwarn -Wno-format"
    fi

    # This should be < 256 really. Currently we're down to 4096,
    # but using 1024 bytes sized buffers (mostly for virStrerror)
    # stops us from going down further
    wantwarn="$wantwarn -Wframe-larger-than=4096"
    dnl wantwarn="$wantwarn -Wframe-larger-than=256"

    # Extra special flags
    dnl -fstack-protector stuff passes gl_WARN_ADD with gcc
    dnl on Mingw32, but fails when actually used
    case $host in
       aarch64-*-*)
       dnl "error: -fstack-protector not supported for this target [-Werror]"
       ;;
       *-*-linux*)
       dnl Prefer -fstack-protector-strong if it's available.
       dnl There doesn't seem to be great overhead in adding
       dnl -fstack-protector-all instead of -fstack-protector.
       dnl
       dnl We also don't need ssp-buffer-size with -all or -strong,
       dnl since functions are protected regardless of buffer size.
       dnl wantwarn="$wantwarn --param=ssp-buffer-size=4"
       wantwarn="$wantwarn -fstack-protector-strong"
       ;;
       *-*-freebsd*)
       dnl FreeBSD ships old gcc 4.2.1 which doesn't handle
       dnl -fstack-protector-all well
       wantwarn="$wantwarn -fstack-protector"

       wantwarn="$wantwarn -Wno-unused-command-line-argument"
       ;;
    esac
    wantwarn="$wantwarn -fexceptions"
    wantwarn="$wantwarn -fasynchronous-unwind-tables"

    # Need -fipa-pure-const in order to make -Wsuggest-attribute=pure
    # fire even without -O.
    wantwarn="$wantwarn -fipa-pure-const"
    # We should eventually enable this, but right now there are at
    # least 75 functions triggering warnings.
    wantwarn="$wantwarn -Wno-suggest-attribute=pure"
    wantwarn="$wantwarn -Wno-suggest-attribute=const"

    if test "$set_werror" = "yes"
    then
      wantwarn="$wantwarn -Werror"
    fi

    # Check for $CC support of each warning
    for w in $wantwarn; do
      gl_WARN_ADD([$w])
    done

    case $host in
        *-*-linux*)
        dnl Fall back to -fstack-protector-all if -strong is not available
        case $WARN_CFLAGS in
        *-fstack-protector-strong*)
        ;;
        *)
            gl_WARN_ADD(["-fstack-protector-all"])
        ;;
        esac
        ;;
    esac

    # Silence certain warnings in gnulib, and use improved glibc headers
    AC_DEFINE([lint], [1],
      [Define to 1 if the compiler is checking for lint.])
    AH_VERBATIM([FORTIFY_SOURCE],
    [/* Enable compile-time and run-time bounds-checking, and some warnings,
        without upsetting newer glibc. */
     #if !defined _FORTIFY_SOURCE && defined __OPTIMIZE__ && __OPTIMIZE__
     # define _FORTIFY_SOURCE 2
     #endif
    ])

    if test "$gl_cv_warn_c__Wlogical_op" = yes &&
       test "$lv_cv_gcc_wlogical_op_broken" = yes; then
      AC_DEFINE_UNQUOTED([BROKEN_GCC_WLOGICALOP], 1,
       [Define to 1 if gcc -Wlogical-op reports false positives on strchr])
    fi
])