[libvirt] [PATCH] build: avoid -Wno-format on new-enough gcc

Commit c579d6b added a sledgehammer to silence spurious warnings from gcc 4.2, but in the process, it also silenced useful warnings from newer gcc (such as 4.4). As a result, a bug slipped in to commit 0caccb58. Tested with FreeBSD (gcc 4.2.1), RHEL 6.3 (gcc 4.4), and F17 (gcc 4.7.2). * m4/virt-compile-warnings.m4 (-Wno-format): Probe for the actual spurious message, to once again allow gcc 4.4 to use -Wformat. --- m4/virt-compile-warnings.m4 | 19 ++++++++++++++++++- 1 file changed, 18 insertions(+), 1 deletion(-) diff --git a/m4/virt-compile-warnings.m4 b/m4/virt-compile-warnings.m4 index d1173eb..f1b8f39 100644 --- a/m4/virt-compile-warnings.m4 +++ b/m4/virt-compile-warnings.m4 @@ -60,6 +60,23 @@ AC_DEFUN([LIBVIRT_COMPILE_WARNINGS],[ # gcc 4.4.6 complains this is C++ only; gcc 4.7.0 implies this from -Wall dontwarn="$dontwarn -Wenum-compare" + # gcc 4.2 treats attribute(format) as an implicit attribute(nonnull), + # which triggers spurious warnings for our usage + AC_CACHE_CHECK([whether gcc -Wformat allows NULL strings], + [lv_cv_gcc_wformat_null_works], [ + save_CFLAGS=$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], @@ -117,7 +134,7 @@ AC_DEFUN([LIBVIRT_COMPILE_WARNINGS],[ # ATTRIBUTE_FMT_PRINT, which causes -Wformat failure on our # intentional use of virReportError(code, NULL). gl_WARN_ADD([-Wno-format-nonliteral]) - if test $lv_cv_gcc_pragma_push_works = no; then + if test $lv_cv_gcc_wformat_null_works = no; then gl_WARN_ADD([-Wno-format]) fi -- 1.7.11.4