Simplify UFFDIO_WRITEPROTECT_MODE_WP Autoconf check

[petk]

AC_CHECK_DECL can check whether preprocessor macro is defined in the given includes.

[nielsdos]

Does this work for macros? The manual for AC_CHECK_DECL talks about symbol (a function, variable, or constant).

[nielsdos]

Ah wait, I get it: This macro actually tests whether it is valid to use symbol as an r-value. So this should indeed be fine.

[petk]

I was also confused about the docs and was hesitating whether to check these with the AC_CHECK_DECL or it would be better to compile and use the #error... :D

This:

AC_CHECK_DECL([UFFDIO_WRITEPROTECT_MODE_WP],,,[#include <linux/userfaultfd.h>]

Will try to compile a program similar to the one below, which works also for the preprocessor macros whether they are defined. A bit of a hack and the macro name abuse, but it works flawlessly and can simplify many things in the future probably. However, all these checking macros must be called after the AC_PROG_CC and AC_USE_SYSTEM_EXTENSIONS calls, so the compiler is determined.

/* confdefs.h */
#define PACKAGE_NAME "PHP"
#define PACKAGE_TARNAME "php"
#define PACKAGE_VERSION "8.4.0-dev"
#define PACKAGE_STRING "PHP 8.4.0-dev"
#define PACKAGE_BUGREPORT "https://github.com/php/php-src/issues"
#define PACKAGE_URL "https://www.php.net"
#define HAVE_STDIO_H 1
#define HAVE_STDLIB_H 1
#define HAVE_STRING_H 1
#define HAVE_INTTYPES_H 1
#define HAVE_STDINT_H 1
#define HAVE_STRINGS_H 1
#define HAVE_SYS_STAT_H 1
#define HAVE_SYS_TYPES_H 1
#define HAVE_UNISTD_H 1
#define HAVE_WCHAR_H 1
#define STDC_HEADERS 1
#define _ALL_SOURCE 1
#define _DARWIN_C_SOURCE 1
#define _GNU_SOURCE 1
#define _HPUX_ALT_XOPEN_SOCKET_API 1
#define _NETBSD_SOURCE 1
#define _OPENBSD_SOURCE 1
#define _POSIX_PTHREAD_SEMANTICS 1
#define __STDC_WANT_IEC_60559_ATTRIBS_EXT__ 1
#define __STDC_WANT_IEC_60559_BFP_EXT__ 1
#define __STDC_WANT_IEC_60559_DFP_EXT__ 1
#define __STDC_WANT_IEC_60559_FUNCS_EXT__ 1
#define __STDC_WANT_IEC_60559_TYPES_EXT__ 1
#define __STDC_WANT_LIB_EXT2__ 1
#define __STDC_WANT_MATH_SPEC_FUNCS__ 1
#define _TANDEM_SOURCE 1
#define __EXTENSIONS__ 1
#define HAVE_GCC_GLOBAL_REGS 1
#define HAVE_CPUID_COUNT 1
#define GWINSZ_IN_SYS_IOCTL 1
#define HAVE_PHPDBG 1
#define PHPDBG_DEBUG 0
#define HAVE_USERFAULTFD_WRITEFAULT 1
#define PHP_WRITE_STDOUT 1
#define HAVE_SOCKET 1
#define HAVE_SOCKETPAIR 1
#define HAVE_HTONL 1
#define HAVE_GETHOSTNAME 1
#define HAVE_GETHOSTBYADDR 1
#define HAVE_LIBDL 1
/* end confdefs.h.  */
#include <linux/userfaultfd.h>

int
main (void)
{
#ifndef UFFDIO_WRITEPROTECT_MODE_WP
#ifdef __cplusplus
  (void) UFFDIO_WRITEPROTECT_MODE_WP;
#else
  (void) UFFDIO_WRITEPROTECT_MODE_WP;
#endif
#endif

  ;
  return 0;
}

[nielsdos]

Yeah that makes sense. Thanks for explaining it!
LGTM