proc_close() returns raw signal number, indistinguishable from normal exit code

Description

On non-Windows systems, when a child process opened via proc_open() is killed by a signal, proc_close() returns the raw signal number (e.g. 11 for SIGSEGV) rather than following the Unix convention of 128 + signal (e.g. 139).

This makes it impossible for PHP userland code to distinguish between "process exited normally with code 11" and "process was killed by SIGSEGV".

Underlying cause

Internally, proc_close() calls waitpid() which returns an encoded status. The C macros WIFEXITED()/WEXITSTATUS() and WIFSIGNALED()/WTERMSIG() exist to decode this, but proc_close() does not use them to differentiate the two cases. It effectively passes back a value that loses the signal/exit distinction.

PHP's own pcntl_waitpid() + pcntl_wifexited() + pcntl_wtermsig() handle this correctly, but pcntl is not always available, and proc_close() is the standard way to get the exit status of a proc_open() process.

Reproduction

<?php

// Child script that triggers SIGSEGV
$child = '<?php posix_kill(posix_getpid(), 11);';

$process = proc_open(
    [PHP_BINARY, '-r', $child],
    [],
    $pipes
);

$exitCode = proc_close($process);

// Expected: 139 (128 + 11, following bash/Unix convention)
// Actual: 11 (raw signal number, same as a normal exit code)
echo "Exit code: $exitCode\n";
echo "Is this SIGSEGV or a normal exit(11)? Impossible to tell.\n";

Expected behavior

proc_close() should return 128 + signal_number when the child was killed by a signal, consistent with how bash and other Unix shells report signal termination via $?. This would allow userland code to detect crashes.

Alternatively, expose the signal information through a separate mechanism (e.g. an optional by-reference parameter, or a new proc_exit_status() function).

Real-world impact

This affects tools that use proc_open() to spawn child processes, notably composer/xdebug-handler which restarts PHP processes. When the child crashes (e.g. due to a PHP JIT bug triggering SIGSEGV), the parent receives exit code 11 with no way to detect it was a signal — leading to silent, misleading failures in tools like Psalm, PHPStan, and Composer.

• Related upstream fix: https://github.com/composer/xdebug-handler/pull/162
• Downstream report: https://github.com/vimeo/psalm/issues/11679

PHP Version

Tested on PHP 8.4 and 8.5, but the behavior has existed since proc_open was introduced.

Operating System

Linux / macOS (any non-Windows POSIX system)

Theo dõi proc_close() trên các hệ thống không phải Windows qua waitpid() và các trường hợp WIFEXITED(), WEXITSTATUS(), WIFSIGNALED() và WTERMSIG() được mô tả trong issue. Chạy bản tái hiện proc_open() được cung cấp với một tiến trình con SIGSEGV và xác minh rằng việc kết thúc do tín hiệu có thể được phân biệt với mã thoát bình thường, đồng thời vẫn giữ nguyên hành vi mong đợi trên các nền tảng khác.