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To: "Dmitry Stogov" <dmitry@zend.com>
Cc: "PHP internals list" <internals@lists.php.net>,
	"Lior Kaplan" <lior.k@zend.com>,
	"Andrea Faulds" <ajf@ajf.me>
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Date: Tue, 22 Dec 2015 14:00:44 -0600
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Subject: Re: [PHP-DEV] Re: Mysterious crashes (WAS: Re: Pear fetch script problem on PHP 7.0)
From: php_lists@realplain.com ("Matt Wilmas")

Hi Dmitry!

----- Original Message -----
From: "Dmitry Stogov"
Sent: Tuesday, December 22, 2015

> Hi Matt,
>
> On Tue, Dec 22, 2015 at 8:36 PM, Matt Wilmas <php_lists@realplain.com>
> wrote:
>
>> Hi all,
>>
>> Lior, which compiler are you using?  You can still reproduce the problem?
>> Can you run it through Valgrind?
>>
>> I'm getting random crashes I can't figure out on 64-bit Linux after just
>> making a very trivial change. :-/  The backtrace is the same up to
>> compile_file() (although maybe that doesn't mean much? hmm).
>>
>> Dmitry, to reproduce, just add another GLOBAL REGISTER variable to
>> zend_vm_execute, and then set it in execute_ex().  An empty file will 
>> crash
>> it.  It does NOT crash with --enable-debug, nor with certain combinations
>> of optimization level and global register.
>>
>
> Using another global register is not a trivial change.

Well, I meant relatively since a couple are already used. ;-)  And thought 
GCC managed it all... (wrong).

>> %r12 with -O2 seems to consistently fail, but with -O3 it might be %r13,
>> etc.
>>
>
> In general both should work fine, but it seems like this feature is not
> well debugged in GCC and may lead to miscompilation.

Right, I remember you requiring min. 4.8 back in the spring after issues 
with earlier versions.  And now I wondered if something was still unstable 
and only working by chance.

>> Now, the question: Is that little change triggering a bug in GCC 4.8?  Or
>> is it somehow revealing a PHP problem?!
>>
>
> It may be a GCC bug, as well as a bug in your code...
> may be you need to save/restore it manually in execute_ex()?

Argh!!  Do I feel dumb. :-(  And that's even what's happening right there 
with the others.  (I was thinking of those as executor-specific 
save/restore, rather than the registers themselves.)   And seems I had it 
reversed thinking the caller would save its own first, which of course is 
wrong for CALLEE-saved regs.

Looks like any combo is working fine now.  I had the changes as a whole all 
working quickly (will reply to your previous subject soon) by luck.  I tried 
everything else after crashes started...  Who knows how long it would've 
taken if not for your reminder! :-)

> Thanks. Dmitry.

Thanks again, and sorry for the noise.

- Matt