Stdlib: system()/passthru() bypass active output buffer — ob_get_clean() empty (ext/standard/exec.c)

[PurHur]

Category

stdlib — shell exec + output buffering

Problem

With an active ob_start() buffer, system() and passthru() must route command stdout into the buffer (Zend does not echo to real stdout). This compiler echoes directly; ob_get_clean() returns an empty string while Zend captures 'hi\n'.

./script/docker-exec.sh -- bash -lc 'source script/php-env.sh && php bin/vm.php test/repro/maintainer_gap_system_ob_capture.php'
# VM stdout leaks "hi" + var_export([\"hi\", \"\"]); Zend: var_export([\"hi\", \"hi\\n\"]) only

Call	Zend ob_get_clean()	This compiler
ob_start(); system('echo hi');	'hi\n'	'' (plus leaked stdout)
ob_start(); passthru('echo hi');	'hi\n'	'' (plus leaked stdout)
exec('echo hi', $out, $code)	populates $out ✓	populates $out ✓

php-src reference

• php/php-src ext/standard/exec.c — php_exec() output routing through SAPI php_output_write()
• php/php-src main/output.c — active output handler chain

Repro

<?php
ob_start();
$r = system('echo hi');
$o = ob_get_clean();
var_export([$r, $o]); // Zend: ['hi', "hi\n"]; VM: ['hi', '']

Committed repro: test/repro/maintainer_gap_system_ob_capture.php.

Scope (PHP-in-PHP)

Path	Work
ext/standard/VmExec.php (or equivalent)	Route system()/passthru() stdout through OB layer / VmOb
ext/standard/VmOb.php	Ensure shell builtins use same write path as echo

Prefer PHP OB integration — no new C exec output path.

Done when (php-src-strict)

• ob_start(); system('echo hi'); ob_get_clean() captures full command output (no stdout leak)
• Same for passthru()
• Return value semantics unchanged (system last line, passthru NULL)
• ./script/docker-exec.sh -- bash -lc 'php bin/vm.php test/repro/maintainer_gap_system_ob_capture.php' matches Zend (no extra stdout)
• Unit/compliance guard under test/compliance/ or test/unit/

Related

• Stdlib: ob_end_clean() extra arguments — LogicException not ArgumentCountError (ext/standard/output.c) #10323 (ob_end_clean arg count) · Epic: Self-host critical path — compiler compiles itself (M3→M5) #1492

[PurHur]

claim: PHP Compiler STD Lib — starting this run

[PurHur]

claim released: repro green on master — maintainer_gap_system_ob_capture.php matches Zend (OB captures hi/hi2 via OutputBuffer::append in VmExecNative::echoToStdout, #13251). Recommend close.

[PurHur]

claim: PHP Compiler STD Lib — starting this run (VM green; AOT compile fails on system_passthru_ob fixture)

[PurHur]

WIP pushed — partial AOT fix in PR (branch agent/issue-10492-process-aot-split).

Fixed: nested-JIT object::iteratekeyed() failure when compiling exec/process helpers. Split phpcRunCommandArgv to ProcessPhpcRunCommandJitHelper.php; lazy-link via ensurePhpcRunCommandLinked(). VM repro green; shell_exec/exec AOT compile green.

Remaining: system()/passthru() AOT still segfaults (exit 139) when JitExec::writeLinesToStdout links ObOutputRuntime — test/aot/AotTest.php --filter system_passthru red. Next step: ObOutputRuntime/ObOutputJitBridge LLVM crash on standalone compile path.