concatenation operator View as Markdown

Hello,

Sorry for the late reply, I was away for a while......
I don't think I have dtrace because I'm on fedora.....but i'll research.

If i would want to set a breakpoint after php's initialization process, but right before the scripts execution, so that after that I can set breakpoints to emalloc and efree which are executed only during my scripts execution where should i set it? Hope the question was clear enough.....

dtrace related:
Why have you used 'execute:return' and not concat_function:return? What's with the execute function?

Thanks,
A.

From: Johannes Schlüter johannes@schlueters.de
To: Adi Mutu adi_mutu06@yahoo.com
Cc: Felipe Pena felipensp@gmail.com; PHP Developers Mailing List internals@lists.php.net
Sent: Thursday, June 7, 2012 11:18 PM
Subject: Re: [PHP-DEV] concatenation operator

Ok Johannes, thanks for the answer. I'll try to look deeper.
I basically just wanted to know what happens when you concatenate two
strings? what emalloc/efree happens.

This depends. As always. As said what has to be done is one allocation
for the result value ... and then the zval magic, which depends on
refcount, references, ...

Also can you tell me if possible how to put a breakpoint to
emalloc/efree which are executed only after all core functions are
registered? because it takes like a million years like this and a
million F8 presses...

Depends on your debugger. Most allow conditional breakpoints or have a
breakpoint and while holding at some place add a few more ...

For such a question my preference is using DTrace (on Solaris, Mac or
BSD), something like this session:

        $ cat test.d
        #!/sbin/dtrace
       
        pid$target::concat_function:entry {
            self->in_concat = 1;
        }
       
        pid$target::execute:return {
            self->in_concat = 0;
        }
       
        pid$target::_emalloc:entry
        / self->in_concat /
        {
            trace(arg0);
            ustack();
        }
       
        pid$target::_erealloc:entry
        / self->in_concat /
        {
            trace(arg0);
            trace(arg1);
            ustack();
        }
       
        $ cat test1.php
        <?php
        $a = "foo"; $b = "bar"; $a.$b;
       
        $ dtrace -s test.d -c 'php test1.php'
        dtrace: script 'test.d' matched 4 probes
        dtrace: pid 16406 has exited
        CPU    ID                    FUNCTION:NAME
          3 100372                  _emalloc:entry                7
                      php_emalloc                       phpconcat_function+0x270
                      phpZEND_CONCAT_SPEC_CV_CV_HANDLER+0xcd                       phpexecute+0x3d9
                      phpdtrace_execute+0xe7                       phpzend_execute_scripts+0xf5
                      phpphp_execute_script+0x2e8                       phpdo_cli+0x864
                      phpmain+0x6e2                       php_start+0x83
       
        $ cat test2.php
        <?php
        $a = 23; $b = "bar"; $a.$b;
       
        $ dtrace -s test.d -c 'php test2.php'
        dtrace: script 'test.d' matched 4 probes
        dtrace: pid 16425 has exited
        CPU    ID                    FUNCTION:NAME
          1 100373                  _erealloc:entry                0              79
                      php_erealloc                       phpxbuf_format_converter+0x11ee
                      phpvspprintf+0x34                       phpzend_spprintf+0x2f
                      php_convert_to_string+0x174                       phpzend_make_printable_zval+0x5ec
                      phpconcat_function+0x3c                       phpZEND_CONCAT_SPEC_CV_CV_HANDLER+0xcd
                      phpexecute+0x3d9                       phpdtrace_execute+0xe7
                      phpzend_execute_scripts+0xf5                       phpphp_execute_script+0x2e8
                      phpdo_cli+0x864                       phpmain+0x6e2
                      php_start+0x83                   1 100372                  _emalloc:entry                6                       php_emalloc
                      phpconcat_function+0x270                       phpZEND_CONCAT_SPEC_CV_CV_HANDLER+0xcd
                      phpexecute+0x3d9                       phpdtrace_execute+0xe7
                      phpzend_execute_scripts+0xf5                       phpphp_execute_script+0x2e8
                      phpdo_cli+0x864                       phpmain+0x6e2
                      php`_start+0x83
       
So, when having two constant strings there's a single malloc, in this
case allocating 7 bytes (strlen("foo")+strlen("bar")+1), if you have a
different type it has to be converted first ...

johannes