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_li...@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
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