From: "hsbt (Hiroshi SHIBATA) via ruby-core" <ruby-core@...>
Date: 2026-09-16T00:44:10+00:00
Subject: [ruby-core:126732] [Ruby Bug#22311] Build crashes on macOS 26 with the macOS 27 SDK because pipe2() and dup3() are unavailable

Issue #22311 has been updated by hsbt (Hiroshi SHIBATA).


The same report came to ruby-build as https://github.com/rbenv/ruby-build/issues/2640, and I worked it around there in https://github.com/rbenv/ruby-build/pull/2641. When the build host is older than macOS 27, ruby-build now exports `ac_cv_func_dup3=no` and `ac_cv_func_pipe2=no` before running `configure`. Neither function is callable at runtime on such a host whatever SDK is installed, so this only restores what the macOS 26 SDK used to produce.

The same two cache variables are enough when building a released tarball by hand.

```
ac_cv_func_dup3=no ac_cv_func_pipe2=no ./configure
```

Unlike `SDKROOT`, this needs no older SDK on the machine. A fresh Command Line Tools 27 install ships only `MacOSX.sdk`, which is 27.

In case a backport is considered, commit:6bfde8d2a239a9e8549de1ae29acecdefdfb8086 applies cleanly to `v4.0.7` and `v3_4_10`. On `v3_3_12` only the last hunk fails, and it is unnecessary there because `ruby_popen_writer` already goes through `rb_cloexec_pipe`.

----------------------------------------
Bug #22311: Build crashes on macOS 26 with the macOS 27 SDK because pipe2() and dup3() are unavailable
https://bugs.ruby-lang.org/issues/22311#change-119027

* Author: himura467 (Akito Shitara)
* Status: Closed
* Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN
----------------------------------------
## Environment

- macOS 26.6.2
- Command Line Tools with MacOSX27.0.sdk (default `MacOSX.sdk`)
- Apple clang version 21.0.0 (clang-2100.3.34.2)

## Steps to reproduce

    ./autogen.sh
    mkdir build && cd build
    ../configure
    make

## Result

The build warns about `dup3` and `pipe2`, and then miniruby crashes:

    ../io.c:389:19: warning: 'dup3' is only available on macOS 27.0 or newer [-Wunguarded-availability-new]
    ../io.c:432:18: warning: 'pipe2' is only available on macOS 27.0 or newer [-Wunguarded-availability-new]
    ../io.c:8141:18: warning: 'pipe2' is only available on macOS 27.0 or newer [-Wunguarded-availability-new]
    ...
    make: *** [uncommon.mk:1331: builtin_binary.rbbin] Segmentation fault: 11

## Cause

The macOS 27 SDK declares `dup3()` and `pipe2()` as available since macOS 27.0.
`AC_CHECK_FUNCS` links them without including headers, so configure defines `HAVE_DUP3` and `HAVE_PIPE2`.
In io.c, they are weakly linked through the header and are NULL at runtime on macOS 26.

    $ nm -m miniruby | grep -E '_(pipe2|dup3) '
                     (undefined) weak external _dup3 (from libSystem)
                     (undefined) weak external _pipe2 (from libSystem)

## Notes

Autoconf 2.73 makes `AC_CHECK_DECL` report "no" for such functions on macOS.

https://github.com/autotools-mirror/autoconf/blob/0a51305fff8847edd3e9da9e538e40c539027aed/NEWS#L125-L126



-- 
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