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 $host in
       aarch64-*-*)
       dnl "error: -fstack-protector not supported for this target [-Werror]"
       ;;
       *-*-linux*)
       dnl Fedora only uses -fstack-protector, but doesn't seem to
       dnl be great overhead in adding -fstack-protector-all instead
       dnl wantwarn="$wantwarn -fstack-protector"
       wantwarn="$wantwarn -fstack-protector-all"
       wantwarn="$wantwarn --param=ssp-buffer-size=4"
       dnl Even though it supports it, clang complains about
       dnl use of --param=ssp-buffer-size=4 unless used with
       dnl the -c arg. It doesn't like it when used with args
       dnl that just link together .o files. Unfortunately
       dnl we can't avoid that with automake, so we must turn
       dnl off the following clang specific warning
       wantwarn="$wantwarn -Wno-unused-command-line-argument"
       ;;
       *-*-freebsd*)
       dnl FreeBSD ships old gcc 4.2.1 which doesn't handle
       dnl -fstack-protector-all well
       wantwarn="$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

    # 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
])