dtrace add prev method and prev class

[tombokombo]

Hi, we are playing around with coroutines etc.. we are using dtrace for debugging and we need to know the caller, so this PR extends existing dtrace probes.

[iluuu1994]

I don't know dtrace, so somebody else should review this 🙂

[devnexen]

question: would not it be better if it had its own scope data ?

[tombokombo]

You are so right, I was overriding it. Haven't noticed that, as scope is basically useless. Fixed.

[devnexen]

I don't know dtrace, so somebody else should review this 🙂

Fair point 🙂 the Dtrace part looks ok if we want all in one probe that's the simplest way but less sure for the zend part.

[tombokombo]

I don't know dtrace, so somebody else should review this slightly_smiling_face

Fair point slightly_smiling_face the Dtrace part looks ok if we want all in one probe that's the simplest way but less sure for the zend part.

In linear execution the probe provides enough info ( caller is known from previous probe call). With co-routines and context switching, you need some hints about caller. I would expect it in same probe, because it's one event (fn entry or return).

[devnexen]

how does a typical line looks line with your change ?

[tombokombo]

@devnexen what do you mean, output from tracing tool?

[devnexen]

yes before and after the changes for example.

[tombokombo]

depend on tracing tool eg with stap https://www.php.net/manual/en/features.dtrace.systemtap.php , it depends on your chosen formatting, basically your are just extracting args

probe process("sapi/cli/php").provider("php").mark("function__entry") {
    printf("Probe function__entry\n");
    printf("  function_name %s\n", user_string($arg1));
    printf("  request_file %s\n", user_string($arg2));
    printf("  lineno %d\n", $arg3);
    printf("  classname %s\n", user_string($arg4));
    printf("  scope %s\n", user_string($arg5));

I'm tracing this probes with bpf, and trying to build callgrind, but for sake of example
before:

ENTRY    - test_ns\Foo.getdata [ /data/tom.php ]
ENTRY    - test_ns\Bar.get [ /data/tom.php ]
RETURN   - test_ns\Bar.get [ /data/tom.php ] spent 1063387247 ns
RETURN   - test_ns\Foo.getdata [ /data/tom.php ] spent 1217172339 ns

This is linear case, time spend is calculated as time between ENTRY and RETURN. You can clearly see call chain
main()->Foo.getData()->Bar.get()
after

ENTRY    test_ns\Foo.getdata [ /data/tom.php ] called by .main 
ENTRY    test_ns\Bar.get [ /data/tom.php ] called by test_ns\Foo.getdata
RETURN   test_ns\Bar.get [ /data/tom.php ] called by test_ns\Foo.getdata spent 1063387247 ns
RETURN   test_ns\Foo.getdata [ /data/tom.php ] called by .main spent 1217172339 ns

Little more complicated example with coroutine, one courutine is calling the same as before
c1 - main()->Foo.getData()->Bar.get()
second one just
c2-> main()->Bar.get()

ENTRY {closure} [ /data/tombo/tom.coroutine.php ] 
ENTRY {closure} [ /data/tombo/tom.coroutine.php ]
ENTRY Foo.getdata [ /data/tombo/tom.coroutine.php ] 
ENTRY {closure} [ /data/tombo/tom.coroutine.php ]
ENTRY Bar.get [ /data/tombo/tom.coroutine.php ] 
RETURN {closure} [ /data/tombo/tom.coroutine.php ]
ENTRY Bar.get [ /data/tombo/tom.coroutine.php ]
RETURN Bar.get [ /data/tombo/tom.coroutine.php ]
RETURN {closure} [ /data/tombo/tom.coroutine.php ]
RETURN Bar.get [ /data/tombo/tom.coroutine.php ]
RETURN Foo.getdata [ /data/tombo/tom.coroutine.php ]
RETURN {closure} [ /data/tombo/tom.coroutine.php ]

the problem is which Bar.get() entry belongs to which return from Bar.get(). But even with information about caller, the problem persist when you call main()->Bar.get() from n-coutroutines, this would need some kind of ID. But I'm creating callgrind and knowing that main called bar-get() n times, should be enough.
Coroutines with this patch

ENTRY {closure} [ /data/tombo/tom.coroutine.php ] called by 
ENTRY {closure} [ /data/tombo/tom.coroutine.php ] called by
ENTRY Foo.getdata [ /data/tombo/tom.coroutine.php ] called by {closure} 
ENTRY {closure} [ /data/tombo/tom.coroutine.php ] called by
ENTRY Bar.get [ /data/tombo/tom.coroutine.php ] called by {closure} 
RETURN {closure} [ /data/tombo/tom.coroutine.php ] called by
ENTRY Bar.get [ /data/tombo/tom.coroutine.php ] called by Foo.getdata 
RETURN Bar.get [ /data/tombo/tom.coroutine.php ] called by {closure} 
RETURN {closure} [ /data/tombo/tom.coroutine.php ] called by
RETURN Bar.get [ /data/tombo/tom.coroutine.php called ] by Foo.getdata 
RETURN Foo.getdata [ /data/tombo/tom.coroutine.php called ] by {closure} 
RETURN .{closure} [ /data/tombo/tom.coroutine.php called by

[devnexen]

Thanks we can have an idea of the added value here indeed.

[dstogov]

I wouldn't like to add these new function to public API.
I won't object of you move their implementation into zend_dtrace.c.

[dstogov]

Sorry, it seems we missed this PR. Only few notes:

• I wouldn't object if get_prev_active_class_name() and get_prev_active_function_name() implementation would be moved into zend_dtrace.c.
• can we test this in some way?