[xdebug-general] Re: xdebug jumps in conditional case.

On Wed, 14 Apr 2010, Xavier Puig wrote:

> My xdebug jumps in IF condition, for example:
>
> 1<?php
> 2 $var="zero"."one"."two"."three";
> 3
> 4 $var2=526;
> 5 if($var2-550 > 0)
> 6 $var=500;
> 7 else
> 8 $var=1000;
> 9 $var="string";
>
> I run dbgp protocol, allways "step_into" and the steps are:
> line 2
> line 4
> line 5
> line 9
>
> I don't know if the conditional was true or false, the only way to know it i
> send command "context_get" and see what value have $var.
>
> Is there any way to know more detail(the maxim) of steps of execution, I must
> have something like this:

<snip>

Xdebug only can break when PHP hits the EXT_STMT opcode. If we check
with VLD and your script, you see they're only at lines 2, 4, 5 and 9:

compiled vars: !0 = $var, !1 = $var2
line # * op fetch ext return operands
---------------------------------------------------------------------------------
   2 0 > EXT_STMT
         1 CONCAT ~0 'zero', 'one'
         2 CONCAT ~1 ~0, 'two'
         3 CONCAT ~2 ~1, 'three'
         4 ASSIGN !0, ~2
   4 5 EXT_STMT
         6 ASSIGN !1, 526
   5 7 EXT_STMT
         8 SUB ~5 !1, 550
         9 IS_SMALLER ~6 0, ~5
   6 10 > JMPZ ~6, ->13
        11 > ASSIGN !0, 500
        12 > JMP ->14
   8 13 > ASSIGN !0, 1000
   9 14 > EXT_STMT
        15 ASSIGN !0, 'string'
  10 16 > RETURN 1

If you change your script to:

<?php
    $var="zero"."one"."two"."three";

    $var2=526;
    if($var2-550 > 0) {
        $var=500;
    } else {
        $var=1000; }
    $var="string";

then more EXT_STMT opcodes are inserted:

compiled vars: !0 = $var, !1 = $var2
line # * op fetch ext return operands
---------------------------------------------------------------------------------
   2 0 > EXT_STMT
         1 CONCAT ~0 'zero', 'one'
         2 CONCAT ~1 ~0, 'two'
         3 CONCAT ~2 ~1, 'three'
         4 ASSIGN !0, ~2
   4 5 EXT_STMT
         6 ASSIGN !1, 526
   5 7 EXT_STMT
         8 SUB ~5 !1, 550
         9 IS_SMALLER ~6 0, ~5
        10 > JMPZ ~6, ->14
   6 11 > EXT_STMT
        12 ASSIGN !0, 500
   7 13 > JMP ->16
   8 14 > EXT_STMT
        15 ASSIGN !0, 1000
   9 16 > EXT_STMT
        17 ASSIGN !0, 'string'
  10 18 > RETURN 1

and Xdebug will correctly break where you expect it. There isn't much I can do
about this, however if you use braces liberally, you won't run into this issue.

Derick

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