glibc 2.25 is deprecating the namespace pollution of sys/types.h injecting major(), minor(), and makedev() into the compilation environment, with a warning that insists that users include <sys/sysmacros.h> instead. However, because the expansion of AC_HEADER_MAJOR didn't bother checking sys/sysmacros.h until after probing whether sys/types.h pollutes the namespace, it was not defining MAJOR_IN_SYSMACROS, with the result that code compiled with -Werror chokes on the deprecation warnings because it was not including sysmacros.h.
In addition to fixing autoconf (which only benefits projects that rebuild configure after this fix is released), we can also give a hint to distros on how they can populate config.site with a cache variable to force pre-existing configure scripts without the updated macro to behave sanely in the presence of glibc 2.25 (the documentation is especially useful since that cache variable is no longer present in autoconf after this patch). Note that mingw lacks major/minor/makedev in any of its standard headers; for that platform, the behavior of this macro is unchanged (code using the recommended include formula will get a compile error when trying to use major(), whether before or after this patch); but for now, it is assumed that programs actually concerned with creating devices are not worried about portability to mingw. If desired, a later patch could tighten AC_HEADER_MAJOR to fail at configure time if the macros are unavailable in any of the three system headers, but that semantic change is not worth mixing into this patch. * lib/autoconf/headers.m4 (AC_HEADER_MAJOR): Drop check for major within sys/types.h; it interferes with the need to check sysmacros.h first. * doc/autoconf.texi (Particular Headers) <AC_HEADER_MAJOR>: Expand details on usage, and on workarounds for non-updated projects. Signed-off-by: Eric Blake <ebl...@redhat.com> --- Thanks for the wordsmithing help, and forcing me to think about mingw. This version updates some wording, and changes the macro to leave the relative order of mkdev.h vs. sysmacros.h checking unchanged (by merely weakining the sys/types.h check to no longer care whether the macros are present). doc/autoconf.texi | 35 +++++++++++++++++++++++++++++++---- lib/autoconf/headers.m4 | 30 ++++++++++++++---------------- 2 files changed, 45 insertions(+), 20 deletions(-) diff --git a/doc/autoconf.texi b/doc/autoconf.texi index d3ccf19..0eb84de 100644 --- a/doc/autoconf.texi +++ b/doc/autoconf.texi @@ -5970,10 +5970,37 @@ Particular Headers @cvindex MAJOR_IN_SYSMACROS @hdrindex{sys/mkdev.h} @hdrindex{sys/sysmacros.h} -If @file{sys/types.h} does not define @code{major}, @code{minor}, and -@code{makedev}, but @file{sys/mkdev.h} does, define -@code{MAJOR_IN_MKDEV}; otherwise, if @file{sys/sysmacros.h} does, define -@code{MAJOR_IN_SYSMACROS}. +Detect the headers required to use @code{makedev}, @code{major}, and +@code{minor}. These functions may be defined by @file{sys/mkdev.h}, +@code{sys/sysmacros.h}, or @file{sys/types.h}. + +@code{AC_HEADER_MAJOR} defines @code{MAJOR_IN_MKDEV} if they are in +@file{sys/mkdev.h}, or @code{MAJOR_IN_SYSMACROS} if they are in +@file{sys/sysmacros.h}. If neither macro is defined, they are either in +@file{sys/types.h} or unavailable. + +To properly use these functions, your code should contain something +like: + +@verbatim +#include <sys/types.h> +#ifdef MAJOR_IN_MKDEV +# include <sys/mkdev.h> +#elif MAJOR_IN_SYSMACROS +# include <sys/sysmacros.h> +#endif +@end verbatim + +Note: Configure scripts built with Autoconf 2.69 or earlier will not +detect a problem if @file{sys/types.h} contains definitions of +@code{major}, @code{minor}, and/or @code{makedev} that trigger compiler +warnings upon use. This is known to occur with GNU libc 2.25, where +those definitions are being deprecated to reduce namespace pollution. +If it is not practical to use Autoconf 2.70 to regenerate the configure +script of affected software, you can work around the problem by setting +@samp{ac_cv_header_sys_types_h_makedev=no}, as an argument to +@command{configure} or as part of a @file{config.site} site default file +(@pxref{Site Defaults}). @end defmac @defmac AC_HEADER_RESOLV diff --git a/lib/autoconf/headers.m4 b/lib/autoconf/headers.m4 index 0c44973..72262c1 100644 --- a/lib/autoconf/headers.m4 +++ b/lib/autoconf/headers.m4 @@ -427,31 +427,29 @@ fi # AC_HEADER_MAJOR # --------------- +# Thanks to glibc 2.25 deprecating macros in sys/types.h, coupled with +# back-compat to autoconf 2.69, we need the following logic: +# Check whether <sys/types.h> compiles. +# If <sys/mkdev.h> compiles, assume it provides major/minor/makedev. +# Otherwise, if <sys/sysmacros.h> compiles, assume it provides the macros. +# Otherwise, either the macros were provided by <sys/types.h>, or do +# not exist on the platform. Code trying to use these three macros is +# assumed to not care about platforms that lack the macros. AN_FUNCTION([major], [AC_HEADER_MAJOR]) AN_FUNCTION([makedev], [AC_HEADER_MAJOR]) AN_FUNCTION([minor], [AC_HEADER_MAJOR]) AN_HEADER([sys/mkdev.h], [AC_HEADER_MAJOR]) AC_DEFUN([AC_HEADER_MAJOR], -[AC_CACHE_CHECK(whether sys/types.h defines makedev, - ac_cv_header_sys_types_h_makedev, -[AC_LINK_IFELSE([AC_LANG_PROGRAM([[@%:@include <sys/types.h>]], - [[return makedev(0, 0);]])], - [ac_cv_header_sys_types_h_makedev=yes], - [ac_cv_header_sys_types_h_makedev=no]) -]) - -if test $ac_cv_header_sys_types_h_makedev = no; then +[AC_CHECK_HEADERS_ONCE([sys/types.h]) AC_CHECK_HEADER(sys/mkdev.h, [AC_DEFINE(MAJOR_IN_MKDEV, 1, [Define to 1 if `major', `minor', and `makedev' are declared in <mkdev.h>.])]) - - if test $ac_cv_header_sys_mkdev_h = no; then - AC_CHECK_HEADER(sys/sysmacros.h, - [AC_DEFINE(MAJOR_IN_SYSMACROS, 1, - [Define to 1 if `major', `minor', and `makedev' - are declared in <sysmacros.h>.])]) - fi +if test $ac_cv_header_sys_mkdev_h = no; then + AC_CHECK_HEADER(sys/sysmacros.h, + [AC_DEFINE(MAJOR_IN_SYSMACROS, 1, + [Define to 1 if `major', `minor', and `makedev' + are declared in <sysmacros.h>.])]) fi ])# AC_HEADER_MAJOR -- 2.7.4