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+# free.m4 serial 6
+# Copyright (C) 2003-2005, 2009-2022 Free Software Foundation, Inc.
+# This file is free software; the Free Software Foundation
+# gives unlimited permission to copy and/or distribute it,
+# with or without modifications, as long as this notice is preserved.
+
+# Written by Paul Eggert and Bruno Haible.
+
+AC_DEFUN([gl_FUNC_FREE],
+[
+ AC_REQUIRE([gl_STDLIB_H_DEFAULTS])
+
+ dnl In the next release of POSIX, free must preserve errno.
+ dnl https://www.austingroupbugs.net/view.php?id=385
+ dnl https://sourceware.org/bugzilla/show_bug.cgi?id=17924
+ dnl So far, we know of three platforms that do this:
+ dnl * glibc >= 2.33, thanks to the fix for this bug:
+ dnl <https://sourceware.org/bugzilla/show_bug.cgi?id=17924>
+ dnl * OpenBSD >= 4.5, thanks to this commit:
+ dnl <https://cvsweb.openbsd.org/cgi-bin/cvsweb/src/lib/libc/stdlib/malloc.c.diff?r1=1.100&r2=1.101&f=h>
+ dnl * Solaris, because its malloc() implementation is based on brk(),
+ dnl not mmap(); hence its free() implementation makes no system calls.
+ dnl For other platforms, you can only be sure if they state it in their
+ dnl documentation, or by code inspection of the free() implementation in libc.
+ AC_CACHE_CHECK([whether free is known to preserve errno],
+ [gl_cv_func_free_preserves_errno],
+ [AC_COMPILE_IFELSE(
+ [AC_LANG_PROGRAM(
+ [[#include <stdlib.h>
+ ]],
+ [[#if 2 < __GLIBC__ + (33 <= __GLIBC_MINOR__)
+ #elif defined __OpenBSD__
+ #elif defined __sun
+ #else
+ #error "'free' is not known to preserve errno"
+ #endif
+ ]])],
+ [gl_cv_func_free_preserves_errno=yes],
+ [gl_cv_func_free_preserves_errno=no])
+ ])
+
+ case $gl_cv_func_free_preserves_errno in
+ *yes)
+ AC_DEFINE([HAVE_FREE_POSIX], [1],
+ [Define if the 'free' function is guaranteed to preserve errno.])
+ ;;
+ *) REPLACE_FREE=1 ;;
+ esac
+])
+
+# Prerequisites of lib/free.c.
+AC_DEFUN([gl_PREREQ_FREE], [:])