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To: Derick Rethans <derick@php.net>
CC: Nikita Popov <nikita.ppv@gmail.com>, PHP Developers Mailing List
	<internals@lists.php.net>
Thread-Topic: Changes to when OPcache initialises
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Date: Mon, 17 Dec 2018 06:44:46 +0000
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Subject: Re: Changes to when OPcache initialises
From: dmitry@zend.com (Dmitry Stogov)

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Hi Derick,


First, check why VLD works out of the box.

At second, you may plug into post_startup hook to reassign zend_compile aft=
er 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=3Dopcache.so  -d "zend_extension=3Dxdebug.so" -d "opca=
che.enable=3D1" -d "opcache.enable_cli=3D1" -d "xdebug.extended_info=3D1" -=
dvld.active=3D1 -f "/home/derick/dev/php/derickr-xdebug/tests/bug00213-php7=
3-opcache.php"
48
/home/derick/dev/php/derickr-xdebug/tests/bug00213-php73-opcache.php:7:
array(4) {
  [5] =3D>
  int(1)
  [8] =3D>
  int(1)
  [12] =3D>
  int(1)
  [14] =3D>
  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=3Dxdebug.so" -dzend_extension=3Dopcache.so -d "opca=
che.enable=3D1" -d "opcache.enable_cli=3D1" -d "xdebug.extended_info=3D1" -=
dvld.active=3D1 -f "/home/derick/dev/php/derickr-xdebug/tests/bug00213-php7=
3-opcache.php"
48
/home/derick/dev/php/derickr-xdebug/tests/bug00213-php73-opcache.php:7:
array(5) {
  [5] =3D>
  int(1)
  [6] =3D>
  int(-2)
  [8] =3D>
  int(1)
  [12] =3D>
  int(1)
  [14] =3D>
  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=3Dopcache.so  -d "zend_extension=3Dxdebug.so" -d "opcac=
he.enable=3D1" -d "opcache.enable_cli=3D1" -d "xdebug.extended_info=3D1" -d=
vld.active=3D1 -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] =3D>
  int(1)
  [6] =3D>
  int(-2)
  [8] =3D>
  int(1)
  [12] =3D>
  int(1)
  [14] =3D>
  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=3Dxdebug.so" -dzend_extension=3Dopcache.so -d "opcac=
he.enable=3D1" -d "opcache.enable_cli=3D1" -d "xdebug.extended_info=3D1" -d=
vld.active=3D1 -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] =3D>
  int(1)
  [6] =3D>
  int(-2)
  [8] =3D>
  int(1)
  [12] =3D>
  int(1)
  [14] =3D>
  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 =3D $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 chang=
e
to the loading order. This was done in:
https://github.com/php/php-src/commit/b4903aef16ec215f2095ff0a3615524656401=
660:

        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 pha=
se (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 =97 *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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