Changes to when OPcache initialises

Hi,

VLD is not a zend extension, so gets loaded/initialised later anyway.
And it seems your hint with post_startup works. I'd appreciate if you
could have a look at my change though:

https://github.com/xdebug/xdebug/commit/3ef3c63ffc831426a45439dbf8b56b998f84d5b1

cheers,
Derick

Hi Derick,

First, check why VLD works out of the box.

At second, you may plug into post_startup hook to reassign zend_compile after opcache.

Thanks. Dmitry.

---

From: Derick Rethans derick@php.net
Sent: Saturday, December 15, 2018 10:01:37 PM
To: Dmitry Stogov
Cc: Nikita Popov; PHP Developers Mailing List
Subject: Changes to when OPcache initialises

Hi!

I am working on making Xdebug work properly with PHP 7.3, and over the
last week I have been tearing my hair out as to why Xdebug's view of
opcodes was no longer showing the opcodes that OPcache had
modified/optimised. In PHP 7.2, the order in which you load Xdebug and
OPcache made a difference.

OPcache optimises out line 6, which has dead code:

1 <?php
2
3 try
4 {
5 throw new Exception();
6 echo strlen( "Revenge is a dish best served cold.\n" );
7 }
8 catch(Exception $e)
9 {
10 }
11
12 echo strlen( "The fire is always hotter on someone elses face." ), "\n";
13 ?>

derick@singlemalt:~/dev/php/derickr-xdebug $ /usr/local/php/7.2.13/bin/php -n -dzend_extension=opcache.so -d "zend_extension=xdebug.so" -d "opcache.enable=1" -d "opcache.enable_cli=1" -d "xdebug.extended_info=1" -dvld.active=1 -f "/home/derick/dev/php/derickr-xdebug/tests/bug00213-php73-opcache.php"
48
/home/derick/dev/php/derickr-xdebug/tests/bug00213-php73-opcache.php:7:
array(4) {
[5] =>
int(1)
[8] =>
int(1)
[12] =>
int(1)
[14] =>
int(1)
}

[GIT: issue1598-no-code-coverage-with-opcache][PHP: 7.2.13 ]
derick@singlemalt:~/dev/php/derickr-xdebug $ /usr/local/php/7.2.13/bin/php -n -d "zend_extension=xdebug.so" -dzend_extension=opcache.so -d "opcache.enable=1" -d "opcache.enable_cli=1" -d "xdebug.extended_info=1" -dvld.active=1 -f "/home/derick/dev/php/derickr-xdebug/tests/bug00213-php73-opcache.php"
48
/home/derick/dev/php/derickr-xdebug/tests/bug00213-php73-opcache.php:7:
array(5) {
[5] =>
int(1)
[6] =>
int(-2)
[8] =>
int(1)
[12] =>
int(1)
[14] =>
int(1)
}

Where as with PHP 7.3.0, they both show the unoptimised version:

derick@singlemalt:~/dev/php/derickr-xdebug $ /usr/local/php/7.3.0/bin/php -n -dzend_extension=opcache.so -d "zend_extension=xdebug.so" -d "opcache.enable=1" -d "opcache.enable_cli=1" -d "xdebug.extended_info=1" -dvld.active=1 -f "/home/derick/dev/php/derickr-xdebug/tests/bug00213-php73-opcache.php"
48
/home/derick/dev/php/derickr-xdebug/tests/bug00213-php73-opcache.php:7:
array(5) {
[5] =>
int(1)
[6] =>
int(-2)
[8] =>
int(1)
[12] =>
int(1)
[14] =>
int(1)
}
[GIT: issue1598-no-code-coverage-with-opcache][PHP: 7.2.13 ]
derick@singlemalt:~/dev/php/derickr-xdebug $ /usr/local/php/7.3.0/bin/php -n -d "zend_extension=xdebug.so" -dzend_extension=opcache.so -d "opcache.enable=1" -d "opcache.enable_cli=1" -d "xdebug.extended_info=1" -dvld.active=1 -f "/home/derick/dev/php/derickr-xdebug/tests/bug00213-php73-opcache.php"
48
/home/derick/dev/php/derickr-xdebug/tests/bug00213-php73-opcache.php:7:
array(5) {
[5] =>
int(1)
[6] =>
int(-2)
[8] =>
int(1)
[12] =>
int(1)
[14] =>
int(1)
}

Curiously, vld, would always show the right (optimised) opcodes:

filename: /home/derick/dev/php/derickr-xdebug/tests/bug00213.inc
function name: (null)
number of ops: 12
compiled vars: !0 = $e
line #* E I O op fetch ext return operands

5 0 E > EXT_STMT
1 NEW $1 :-5
2 EXT_FCALL_BEGIN
3 DO_FCALL 0
4 EXT_FCALL_END
5 > THROW 0 $1
8 6 E > > CATCH 'Exception', !0
12 7 > EXT_STMT
8 ECHO 48
9 EXT_STMT
10 ECHO '%0A'
14 11 > RETURN 1

branch: # 0; line: 5- 5; sop: 0; eop: 5; out0: -2
branch: # 6; line: 8- 8; sop: 6; eop: 6; out0: 7; out1: -2
branch: # 7; line: 12- 14; sop: 7; eop: 11; out0: -2
path #1: 0,
path #2: 6, 7,

So I did some digging and found out that OPcache in PHP 7.3 has had a change
to the loading order. This was done in:
https://github.com/php/php-src/commit/b4903aef16ec215f2095ff0a3615524656401660:

    commit b4903aef16ec215f2095ff0a3615524656401660
    Author: Dmitry Stogov <dmitry@zend.com>
    Date:   Wed Oct 18 17:18:54 2017 +0300

            Move a part of opcache initialization into post_startup phase (when all extensions already loaded).

Both Xdebug and OPcache hook into zend_compile. In PHP 7.2, when as per
documentation, OPcache was loaded after Xdebug, OPcache's zend_compile
(accel_startup) was run first, so that Xdebug sees the optimised
opcodes.

In PHP 7.3, after the above commit, Xdebug's zend_compile hook
(xdebug_compile_file) is run before OPcache's — no matter which
extension is loaded first. Due to this, Xdebug can not properly do code
coverage anymore when OPcache is also present, as it can only see
unoptimised oparrays during its zend_compile hook.

Because opcodes may now differ between when Xdebug analyses oparrays
(zend_compile stage) and when it uses it (zend_execute stage) the
results can be inconsistent in OPcache has optimised things away, and/or
rearranged branches.

Right now, I don't think I have a choice but to disallow code coverage
analysis when OPcache is present, but I would prefer finding a solution
to this so that OPcache and Xdebug work together again, as it did for
PHP versions before 7.3.

cheers,
Derick

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