+ AH_VERBATIM([async_safe],
+[/* The _GL_ASYNC_SAFE marker should be attached to functions that are
+ signal handlers (for signals other than SIGABRT, SIGPIPE) or can be
+ invoked from such signal handlers. Such functions have some restrictions:
+ * All functions that it calls should be marked _GL_ASYNC_SAFE as well,
+ or should be listed as async-signal-safe in POSIX
+ <https://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html#tag_15_04>
+ section 2.4.3. Note that malloc(), sprintf(), and fwrite(), in
+ particular, are NOT async-signal-safe.
+ * All memory locations (variables and struct fields) that these functions
+ access must be marked 'volatile'. This holds for both read and write
+ accesses. Otherwise the compiler might optimize away stores to and
+ reads from such locations that occur in the program, depending on its
+ data flow analysis. For example, when the program contains a loop
+ that is intended to inspect a variable set from within a signal handler
+ while (!signal_occurred)
+ ;
+ the compiler is allowed to transform this into an endless loop if the
+ variable 'signal_occurred' is not declared 'volatile'.
+ Additionally, recall that:
+ * A signal handler should not modify errno (except if it is a handler
+ for a fatal signal and ends by raising the same signal again, thus
+ provoking the termination of the process). If it invokes a function
+ that may clobber errno, it needs to save and restore the value of
+ errno. */
+#define _GL_ASYNC_SAFE
+])
+ dnl Hint which direction to take regarding cross-compilation guesses:
+ dnl When a user installs a program on a platform they are not intimately
+ dnl familiar with, --enable-cross-guesses=conservative is the appropriate
+ dnl choice. It implements the "If we don't know, assume the worst" principle.
+ dnl However, when an operating system developer (on a platform which is not
+ dnl yet known to gnulib) builds packages for their platform, they want to
+ dnl expose, not hide, possible platform bugs; in this case,
+ dnl --enable-cross-guesses=risky is the appropriate choice.
+ dnl Sets the variables
+ dnl gl_cross_guess_normal (to be used when 'yes' is good and 'no' is bad),
+ dnl gl_cross_guess_inverted (to be used when 'no' is good and 'yes' is bad).
+ AC_ARG_ENABLE([cross-guesses],
+ [AS_HELP_STRING([--enable-cross-guesses={conservative|risky}],
+ [specify policy for cross-compilation guesses])],
+ [if test "x$enableval" != xconservative && test "x$enableval" != xrisky; then
+ AC_MSG_WARN([invalid argument supplied to --enable-cross-guesses])
+ enableval=conservative
+ fi
+ gl_cross_guesses="$enableval"],
+ [gl_cross_guesses=conservative])
+ if test $gl_cross_guesses = risky; then
+ gl_cross_guess_normal="guessing yes"
+ gl_cross_guess_inverted="guessing no"
+ else
+ gl_cross_guess_normal="guessing no"
+ gl_cross_guess_inverted="guessing yes"
+ fi