gh-153711: Test availability for dup3() and pipe2() on iOS (#155222)

Modifies the configure test for dup3 and pipe2 to allow for iOS. These symbols
exist, but are unlinkable on iOS 26.

Co-authored-by: Russell Keith-Magee <russell@keith-magee.com>
Co-authored-by: Ned Deily <nad@python.org>

Author: 3 people

Doc/library/os.rst

@@ -1479,7 +1479,7 @@ or `the MSDN <https://msdn.microsoft.com/en-us/library/z0kc8e3z.aspx>`_ on Windo
    Return a pair of file descriptors ``(r, w)`` usable for reading and writing,
    respectively.
 
-   .. availability:: Unix, macOS >= 27.0, not WASI, not iOS.
+   .. availability:: Unix, macOS >= 27.0, iOS >= 27.0, not WASI.
 
    .. versionadded:: 3.3
 

Misc/NEWS.d/next/Library/2026-08-05-10-13-23.gh-issue-153711.9g9dVz.rst

@@ -0,0 +1,3 @@
+On iOS, add :func:`os.pipe2`, and use the syscalls :manpage:`pipe2 (2)` and
+:manpage:`dup3 (2)` internally, when available at both build-time and
+run-time.

Modules/posixmodule.c

@@ -513,8 +513,8 @@ static const unsigned int _Py_STATX_KNOWN = (STATX_BASIC_STATS | STATX_BTIME
 #  define HAVE_MKFIFOAT_RUNTIME __builtin_available(macOS 13.0, iOS 16.0, tvOS 16.0, watchOS 9.0, *)
 #  define HAVE_MKNODAT_RUNTIME __builtin_available(macOS 13.0, iOS 16.0, tvOS 16.0, watchOS 9.0, *)
 #  define HAVE_PTSNAME_R_RUNTIME __builtin_available(macOS 10.13.4, iOS 11.3, tvOS 11.3, watchOS 4.3, *)
-#  define HAVE_DUP3_RUNTIME __builtin_available(macOS 27.0, *)
-#  define HAVE_PIPE2_RUNTIME __builtin_available(macOS 27.0, *)
+#  define HAVE_DUP3_RUNTIME __builtin_available(macOS 27.0, iOS 27.0, tvOS 27.0, watchOS 27.0, visionOS 27.0, *)
+#  define HAVE_PIPE2_RUNTIME __builtin_available(macOS 27.0, iOS 27.0, tvOS 27.0, watchOS 27.0, visionOS 27.0, *)
 
 #  define HAVE_POSIX_SPAWN_SETSID_RUNTIME __builtin_available(macOS 10.15, *)
 

configure

@@ -439,7 +439,7 @@ if test -z "$AR"; then
 		aarch64-apple-ios*)           AR=arm64-apple-ios-ar ;;
 		x86_64-apple-ios*-simulator)  AR=x86_64-apple-ios-simulator-ar ;;
 		*)
-	esac
+    esac
 fi
 if test -z "$CC"; then
 	case "$host" in
@@ -5605,9 +5605,24 @@ fi
 # found by configure), but either raise a compilation error (because the
 # header definition prevents usage - autoconf doesn't use the headers), or
 # raise an error if used at runtime. Force these symbols off.
-if test "$ac_sys_system" != "iOS" ; then
-  AC_CHECK_FUNCS([dup3 getentropy getgroups pipe2 system])
-fi
+# In particular, dup3 and pipe2 are available as of iOS 27 but were
+# incorrectly detected in older simulator versions.
+case "$ac_sys_system" in
+    iOS)
+        AC_MSG_CHECKING([if iOS SDK is older than 27])
+        ios_sdk_version=$(xcrun --sdk iphoneos --show-sdk-version 2>/dev/null | cut -d. -f1)
+        if test -n "$ios_sdk_version" && test "$ios_sdk_version" -ge 27; then
+            AC_MSG_RESULT([no])
+            AC_CHECK_FUNCS([dup3 pipe2])
+        else
+            AC_MSG_RESULT([yes])
+        fi
+        ;;
+    *)
+        # not iOS
+        AC_CHECK_FUNCS([dup3 getentropy getgroups pipe2 system])
+        ;;
+esac
 
 AC_CHECK_DECL([dirfd],
               [AC_DEFINE([HAVE_DIRFD], [1],