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Bug #80447 Strange out of memory error when running with JIT
Submitted: 2020-11-30 20:21 UTC Modified: 2020-12-01 13:49 UTC
From: dac514 at hotmail dot com Assigned: dmitry (profile)
Status: Closed Package: JIT
PHP Version: 8.0.0 OS: Ubuntu
Private report: No CVE-ID: None
 [2020-11-30 20:21 UTC] dac514 at hotmail dot com
Description:
------------
In the last few days benchmarksgame-team.pages.debian.net upgraded to PHP8.

This script;

https://benchmarksgame-team.pages.debian.net/benchmarksgame/program/binarytrees-php-4.html

When run with JIT:

`/opt/src/php-8.0.0/bin/php -dzend_extension=/opt/src/php-8.0.0/lib/php/extensions/no-debug-non-zts-20200930/opcache.so -dopcache.enable_cli=1 -dopcache.jit_buffer_size=64M -n -d memory_limit=4096M binarytrees.php-4.php 21`

Runs out of memory, very unusually, (it did not run out of memory in previous versions of PHP)

The following weird hack is a workaround, change:

```
function createTree($depth)
{
    if (!$depth) {
        return [null, null];

```

To:

```
function createTree($depth)
{
    echo '';
    if (!$depth) {
        return [null, null];
```

I don't get it?


Test script:
---------------
function createTree($depth)
{
    // echo ''; // TODO: This hack works?!
    if (!$depth) {
        return [null, null];
    }
    $depth--;

    return [
        createTree($depth),
        createTree($depth)
    ];
}

function checkTree($treeNode)
{
    return 1
        + ($treeNode[0][0] === null ? 1 : checkTree($treeNode[0]))
        + ($treeNode[1][0] === null ? 1 : checkTree($treeNode[1]));
}

$minDepth = 4;
$n = ($argc == 2) ? $argv[1] : 1;
$maxDepth = max($minDepth + 2, $n);
$stretchDepth = $maxDepth + 1;

$stretchTree = createTree($stretchDepth);
echo "stretch tree of depth $stretchDepth\t check: ", checkTree($stretchTree), PHP_EOL;
unset($stretchTree);

$longLivedTree = createTree($maxDepth);

function startWorker($depth, $iter, $n, $size, $shmId)
{
    $pid = pcntl_fork();
    if ($pid) {
        return $pid;
    } else {
        $check = 0;
        for ($i = 1; $i <= $iter; ++$i) {
            $t = createTree($depth);
            $check += checkTree($t);
            unset($t);
        }
        $result = "$iter\t trees of depth $depth\t check: $check\n";
        shmop_write($shmId, $result, $size * ($n - 1));
        exit(0);
    }
}

$iterations = 1 << ($maxDepth);
$depthIterations = [$minDepth => $iterations];
do {
    $minDepth += 2;
    if ($minDepth <= $maxDepth) {
        $iterations >>= 2;
        $depthIterations[$minDepth] = $iterations;
    }
} while ($minDepth <= $maxDepth);

extension_loaded('shmop') or dl('shmop.so');
$size = 128;
$shmId = shmop_open(ftok(__FILE__, 'b'), 'c', 0644, $size * (count($depthIterations) + 1));
$PIDs = [];
$n = 0;
foreach ($depthIterations as $d => $i) {
    $PIDs[] = startWorker($d, $i, ++$n, $size, $shmId);
}
foreach ($PIDs as $PID) {
    pcntl_waitpid($PID, $status);
}
foreach (range(1, count($depthIterations)) as $n) {
    echo trim(shmop_read($shmId, $size * ($n - 1), $size)), PHP_EOL;
}
shmop_delete($shmId);

echo "long lived tree of depth $maxDepth\t check: ", checkTree($longLivedTree), PHP_EOL;

Expected result:
----------------
PROGRAM OUTPUT:
stretch tree of depth 22	 check: 8388607
2097152	 trees of depth 4	 check: 65011712
524288	 trees of depth 6	 check: 66584576
131072	 trees of depth 8	 check: 66977792
32768	 trees of depth 10	 check: 67076096
8192	 trees of depth 12	 check: 67100672
2048	 trees of depth 14	 check: 67106816
512	 trees of depth 16	 check: 67108352
128	 trees of depth 18	 check: 67108736
32	 trees of depth 20	 check: 67108832
long lived tree of depth 21	 check: 4194303

Actual result:
--------------
Out of memory error. Terminated.

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History

AllCommentsChangesGit/SVN commitsRelated reports
 [2020-11-30 20:23 UTC] dac514 at hotmail dot com
Upstream ticket: https://salsa.debian.org/benchmarksgame-team/benchmarksgame/-/issues/401
 [2020-11-30 20:24 UTC] cmb@php.net
-Package: Unknown/Other Function +Package: JIT
 [2020-12-01 10:54 UTC] nikic@php.net
-Status: Open +Status: Verified -Assigned To: +Assigned To: dmitry
 [2020-12-01 13:47 UTC] dmitry@php.net
Automatic comment on behalf of dmitry@zend.com
Revision: http://git.php.net/?p=php-src.git;a=commit;h=44475e70e2d29c862c58827ae72975205123b4a2
Log: Fixed bug #80447 (Strange out of memory error when running with JIT)
 [2020-12-01 13:47 UTC] dmitry@php.net
-Status: Verified +Status: Closed
 
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