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Date: Thu, 8 Jan 2015 09:56:43 -0800
Cc: Derick Rethans <derick@php.net>,
 PHP internals <internals@lists.php.net>,
 Sara Golemon <pollita@php.net>,
 Stanislav Malyshev <smalyshev@gmail.com>,
 =?utf-8?Q?Fran=C3=A7ois_Laupretre?= <francois@tekwire.net>,
 Benjamin Eberlei <kontakt@beberlei.de>
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References: <CAEPJdu=2oWiSCQOTkO1g5QDs4NrJwd5H14Jks17qrNu7-eQNVg@mail.gmail.com> <CAESVnVqAHJujo0anMi7QYhSZeErcfRVAJ=M7oQMG-huk-bxpCg@mail.gmail.com> <54AAF98B.4020709@gmail.com> <alpine.DEB.2.11.1501061120440.4080@whisky.home.derickrethans.nl> <CAEZPtU69a2MwH5aqigAUEp8+KcjR+w9pd81EvzvM1_z4ES34rQ@mail.gmail.com> <001b01d029bb$fa687fc0$ef397f40$@tekwire.net> <alpine.DEB.2.11.1501070959000.4080@whisky.home.derickrethans.nl> <CAEZPtU67htboPTt6PefLaEREbkobnPY=BpjKpRGg3B1o8xC0Vg@mail.gmail.com>
To: Pierre Joye <pierre.php@gmail.com>
Subject: Re: [PHP-DEV] [RFC] Extension Prepend Files
From: fred@fredemmott.co.uk (Fred Emmott)


> On Jan 7, 2015, at 2:18 AM, Pierre Joye <pierre.php@gmail.com> wrote:
>> That's very much the case. One extension, one "install". It doesn't
>> matter whether some of the extension is written in C, and other parts =
in
>> PHP. HHVM is *all* about this. Making use of C where you need it, and
>> otherwise just write the simpler *but integral* border functionality =
in
>> PHP for faster maintenance and development.
>=20
> It is not correct nor relevant to compare hhvm extension development =
with
> this case. With hhvm it ends up with an actual native extension while =
here
> it is proposed to bundled script that will be executed at runtime like =
any
> other script, except that nothing can be done with them, not even =
disable
> them if not required (like using its own glue codes).


Both HHVM and its' extensions embed PHP source in the binaries.

In our experience:
+ bundling them together makes it much quicker to iterate and improve =
extensions.
+ the PHP code tends to use =E2=80=98non-public=E2=80=99 parts of the C =
API - so it really needs to be kept in sync with the PHP version. I=E2=80=99=
m not sure if composer currently supports =E2=80=98if I=E2=80=99m on PHP =
5.6.0 use this library, if I=E2=80=99m on 5.6.1 use this library=E2=80=A6=E2=
=80=99. While this is fixable, it seems like a lot of boilerplate.
+ If PHP7 does develop a JIT, the PHP implementations could be faster =
than calling the C code (type specializing, and the overhead of setting =
up the stack for a C function call). This is often the case for HHVM.
- we currently do not support extension-style parameter coercion in PHP =
functions; this leads to small incompatibilities in our case, which we =
usually address by writing a C++ function that proxies to a hidden PHP =
implementation. For PHP7, if the current scalar types RFC lands, this =
won=E2=80=99t be a problem; if it doesn=E2=80=99t, there=E2=80=99s a =
chance that multiple functions from the same extension will have =
confusingly different parameter coercing behavior, depending on the =
author=E2=80=99s rigor.

We solved some of the other problems by only allowing definitions, no =
side-effects - classes, constants, namespaces etc. We do not allow code =
outside of a function body here.



HHVM-specific details (just FYI, agree that they=E2=80=99re probably not =
particularly relevant):

* We do not translate the PHP source to native code (unless it ends up =
being jitted at runtime)

* We=E2=80=99re planning on supporting the extension-style coercion in =
Hack code with a user attribute

* To dig the code out:

$ objdump -h hhvm | egrep =E2=80=98 (ext|systemlib)=E2=80=99 # also =
works for a dynamic extension .so
=E2=80=A6
149 ext.ff104b2dfab9 00002410  0000000000000000  0000000000000000  =
02d350a5  2**0
150 systemlib     000766a2  0000000000000000  0000000000000000  02d374b5 =
 2**0
$ objdump -s -j systemlib hhvm | head -n 20

hhvm:     file format elf64-x86-64

Contents of section systemlib:
 00000 3c3f6868 0a2f2f20 7b407d67 656e6572  <?hh.// {@}gener
 00010 61746564 0a0a6e61 6d657370 61636520  ated..namespace
 00020 7b0a0a2f 2f206465 6661756c 74206261  {..// default ba
 00030 73650a63 6c617373 20737464 436c6173  se.class stdClas
 00040 73207b0a 7d0a0a2f 2f207573 65642069  s {.}..// used i
 00050 6e20756e 73657269 616c697a 65282920  n unserialize()
 00060 666f7220 756e6b6e 6f776e20 636c6173  for unknown clas
 00070 7365730a 636c6173 73205f5f 5048505f  ses.class __PHP_
 00080 496e636f 6d706c65 74655f43 6c617373  Incomplete_Class
 00090 207b0a20 20707562 6c696320 245f5f50   {.  public $__P
 000a0 48505f49 6e636f6d 706c6574 655f436c  HP_Incomplete_Cl
 000b0 6173735f 4e616d65 3b0a7d0a 7d0a0a6e  ass_Name;.}.}..n
 000c0 616d6573 70616365 207b0a0a 2f2f2055  amespace {..// U
 000d0 73656420 61732061 2073656e 74696e65  sed as a sentine
 000e0 6c207479 70652069 6e203836 70696e69  l type in 86pini
 000f0 7428292e 0a636c61 7373205f 5f70696e  t()..class __pin