On Sun, Dec 20, 2015 at 9:06 PM, Derick Rethans <[email protected]> wrote:
> Hi!
>
> I've been making sure Xdebug (and vld) compile with master as well - and
> while doing so I was retrofitting CATCH to use the extended value as a
> relative jump point (instead of absolute). Like:
>
> PHP 7.0:
> vld_printf (stderr, ", ->%d", op.extended_value);
>
> PHP 7.1:
> vld_printf (stderr, ", ->%d", nr + ((int) op.extended_value /
> sizeof(zend_op)));
>
> This works fine, and CATCH now shows:
> 18 46 E > > CATCH
> 'ExceptionFoo', !2, ->50
> again, instead of ->128
>
> However, the last CATCH, has a negative jump back to position 0 in PHP
> 7.1:
>
> 22 54 E > > CATCH
> 'ExceptionBaz', !2, ->0
>
> Instead of what it does for PHP 7.0, jump to after the CATCH state:
>
> 22 54 E > > CATCH
> 'ExceptionBaz', !2, ->57
>
>
> The whole section from VLD is:
>
> 17 43 > EXT_STMT
> 44 ECHO
> 'Not+thrown%0A'
> 45 > JMP
> ->57
> 18 46 E > > CATCH
> 'ExceptionFoo', !2, ->50
> 19 47 > EXT_STMT
> 48 ECHO
> 'caught%0A'
> 49 > JMP
> ->57
> 20 50 E > > CATCH
> 'ExceptionBar', !2, ->54
> 21 51 > EXT_STMT
> 52 ECHO
> 'caught%0A'
> 53 > JMP
> ->57
> 22 54 E > > CATCH
> 'ExceptionBaz', !2, ->0 ***
> 23 55 > EXT_STMT
> 56 ECHO
> 'caught%0A'
> 26 57 > EXT_STMT
> 58 ECHO
> 'And+do+some+more%0A'
> 27 59 EXT_STMT
> 60 > RETURN
> null
>
>
> *** is where the change happens from 57 to 0. However, I can't find *why*
> this
> happens, and whether it is actually correct? In the executor I can't see
> a separate check for "0" either - even if that is correct. What's the deal
> here?
>
> Then again, the logic sees the ->0 or ->57 both as an exit, as
> opcode.result.num == 1 for the 3rd catch. In zend_vm_execute, they do this,
> instead of the jump:
>
> if (opline->result.num) {
> zend_throw_exception_internal(NULL);
> HANDLE_EXCEPTION();
> }
>
> The file for which this happens is
> http://derickrethans.nl/files/dump/bug01034-003.txt
>
> cheers,
> Derick
>
The extended_value JMP_ADDR is only used if opline->result.num is 0.
opline->result.num here serves as a flag whether it is the last catch in
the sequence. If so, there is no further catch to jump to and instead the
exception is rethrown. extended_value will be some meaningless dummy value
in that case.
For VLD you should hide the value if opline->result.num is set, similar to
what zend_dump does:
http://lxr.php.net/xref/PHP_TRUNK/ext/opcache/Optimizer/zend_dump.c#644
Nikita
