Using V8 to generate runtime calls in Functions

[Malek Musleh]

Hi,

I have a 2 part (but semi-related question) here.

1)

I am looking at being able to generate specific runtime calls during the execution of certain JS functions. This can be thought of as having V8 insert calls (annotating function entry/exit points) with calls to an external system library/call (e.g. Calling "ls").

I see there are ways of doing the opposite: invoking v8 from within C++ code: 

https://bungeeconnect.wordpress.com/2008/10/09/connecting-c-to-javascript-via-googles-v8/

But I am sort of looking for the opposite. Is something like the following possible:

 Runtime.getRuntime().exec("ls"); // example invoking runtime from android / Java

2)

My end goal here is to have the code-generator generate additional calls (at the prologue/epilogue) to this external function / library) for functions deemed to be "hot" by crankshaft. For this I presume, Would I need to edit the code-generator part (full-codegen.cc) to generate these extra calls inside these functions, or should it be done elsewhere, perhaps in the lithium generator part?

I should note that I have been able to compile this external library within v8 as a third party tool, and I verified invoking it within v8 works.

Malek

[Malek Musleh]

Doing some more investigating, I am able to narrow down the scope of
my question:
In lithium.cc / fullcode-gen.c I see calls to MakeCodePrologue() and
MakeCodeEpilogue(). Since I am interested in adding to the prologue of
optimized code, I can focus on the lithium.cc part.

Both those call void CodeGenerator::MakeCodePrologue() in codegen.cc,
but I don't see any actual code being "generated" or emitted there.
The call I want to emit is basically just 2 assembly instructions (I
use this as a hint driver for my simulator).

Can I just call emit() from within those makePrologue/Epilogue calls?


Malek

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[Flying Jester]

Doing the first thing you suggest is really not at all related to dealing with the optimizer. Just putting strings from JS into a C++ system exec would not be very difficult.

Unless you want to do something to V8 itself, and are less concerned with actually doing things from JavaScript, I suggest you do not touch the guts of V8.

[Malek Musleh]

For 1) I was trying to do something like this initially:

http://stackoverflow.com/questions/20643470/execute-a-command-line-binary-in-node-js
but it doesn't seem to work with v8 standalone. Might seem like a
trivial example, but would you be able to provide an example that
would work with v8 standalone?