misc/sys/cdefs.h | 15 +++++++++++++++
1 file changed, 15 insertions(+)
@@ -649,6 +649,21 @@ _Static_assert (0, "IEEE 128-bits long double requires redirection on this platf
# define __glibc_macro_warning(msg)
#endif
+/* __glibc_warn_system_headers_begin starts a block of code where warnings
+ produced by expanding macros defined in system headers will *not* be
+ supressed. __glibc_warn_system_headers_end ends such a block. */
+#if __GNUC_PREREQ (4,8)
+# define __glibc_warn_system_headers1(message) _Pragma (#message)
+# define __glibc_warn_system_headers_begin \
+ __glibc_warn_system_headers1 (GCC diagnostic push) \
+ __glibc_warn_system_headers1 (GCC diagnostic warning "-Wsystem-headers")
+# define __glibc_warn_system_headers_end \
+ __glibc_warn_system_headers1 (GCC diagnostic pop)
+#else
+# define __glibc_warn_system_headers_begin
+# define __glibc_warn_system_headers_end
+#endif
+
/* Generic selection (ISO C11) is a C-only feature, available in GCC
since version 4.9. Previous versions do not provide generic
selection, even though they might set __STDC_VERSION__ to 201112L,
By default, GCC supresses warnings inside "system headers". Moreover, it also supresses warnings resulting from expansion of macros defined in system headers, even in the expansion itself happens in user code. This may be desirable most of the time because the user cannot do anything about the mistakes of the system headers, but sometimes causing a warning is an intentional effect that a macro has, in which case this GCC feature gets in a way. GCC allows turning off the warning suspension feature by passing -Wsystem-headers; however, that turns it off globally. But by using "#pragma GCC diagnostic" it can be made to only apply to the relevant macro definition, in which case GCC only does not supress warnings resulting from expansion of that one macro. To that end, introduce __glibc_warn_system_headers_begin and __glibc_warn_system_headers_end macros that can be used to surround a macro definition and ensure that warnings inside the macro are not supressed: __glibc_warn_system_headers_begin #define foo(x) bar_warn (x) __glibc_warn_system_headers_end This will be used in a following patch which turns fcntl and fcntl64 into macros that cause warnings on argument type mismatch. Note that "#pragma GCC diagnostic warning" normally overrides any diagnostic options specified on the command line, and so can even downgrade severity of a diagnostic from an error to a warning (if, for instance, -Werror is in effect). But this is not a concern here, since the actual warning that gets emitted is not "-Wsystem-headers", but some other specific warning; "-Wsystem-headers" is only used to disable its supression. So passing -Werror still causes the specific warning to be treated as an error, and to fail the compilation. Clang does not seem to support turning -Wsystem-headers on and off with a pragma, but does not seem to suppress warnings from system-defined macros either. Hence, the macros added by this patch expand to nothing under Clang. Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> Signed-off-by: Sergey Bugaev <bugaevc@gmail.com> ---