How to Build a Virtual Machine

Terence Parr gives an idea of the core mechanisms behind virtual machines by building one, in front of your eyes, from scratch. It is the same kind of commercial interpreter he made for Renault cars.

[ryanlunger]

I watched this video mainly because I admire Mr. Parr for his work.  I enjoy the particulars of language design and implementation, so I knew starting out that this was going to cover pretty basic stuff.  But I really appreciate and enjoy presentations given in this very informal way. My first C++ class was very much like this.  There was a handful of us in the class, and with our instructor's involvement we would democratically discuss and design the solution to some particular assignment.  A great deal of the more advanced stuff really sank in during those times. 

[philipp]

Awesome video, had some initial problems, but after debugging I found the issue and now I am a proud creator of a VM!

[mmille]

I started trying to read the (last) implementation chapter of "Smalltalk-80: The Language and its Implementation, " and got lost rather quickly. I got here after reading Chap. 7 of "Squeak: Open Personal Computing and Multimedia, " where it talked about the VM implementation. Now, some basics are coming together in my head. Great talk!

[avwie]

When you close your eyes it sounds like Tom Hanks is talking

[ivand]

It is worth mentioning that probably the the first one was the FORTH virtual machine

[ThaerRazeq]

The fastest way of doing this other than generating native code manually, is by generating c code and compile that with llvm and run it at runtime. This is similar to how unreal script or valve's half life SDK do it. But I think iOS and Mac don't allow this for security reasons due to the potential malicious modifications.

[petercheung]

better to have english subtitle for this wonderful video for non native english speaker

[kovertopz]

I've written a tree interpreter for a small DSL. Traversing the tree isn't that bad. Creating the tree to me is difficult since you have to create one that represents the order of operations. My grammar was very restricted and I should have went with something like a Pratt parser.

[blenderpanzi]

A tree based interpreter has one application: When you have a throw-away expression that is only executed once. E.g. a input field where a user can input a value via an expression that gets immediately evaluated and replaced with its value. (Blender 3D has these, IIRC. But I think it simply uses Python for that.) Also I don't find tree based interpreters harder than others, but then I haven't built complex interpreters. Only very basic stuff (simple mathematical functions with only one data type (number)).

[BryanChance]

How does the CPU do anything in the first place. That's what I want to know. Too low level?

[guilhermesaraiva]

there are any book about this subject that guy is talked, building VM step by step i did not find it

[karlmin]

He looks like Harrison Wells in The Flash, even his modal.

[solaxun]

Great video, helped clear up many of the questions I had about how bytecode VM's work (along with his book).

One thing I do not understand though, is how compiled function code shares the same array as the rest of the code (see 1:23:05 discussing function calls). I can see how jumping to the address of a function's code works during the interpretation of "call" instruction, but how do we avoid running into sections of compiled function code while just normally stepping through the code array (as we increment the instruction pointer)? Is a portion of the code array effectively blocked off for function use exclusively, and the compiler handles this separation during compilation?

[danielsmith]

14:24 I'm still in shock that universities exist that don't introduce assembly language.

[jeanclaudescandale]

Hi, Why not using a data stack and a return stack ? each instruction, beside push, could pops its arguments from the stack only and the compiler could use macros to avoid the hassle of using too many pushes and pops;
Like jmpz could be inlined :
push addr
push 0
sub
jmpz
What do you thinks ?

[peterfireflylund]

Is it just me or is the 6502 memcpy code he shows in the beginning buggy?

I think it decrements Y (CNT.L) outside the inner loop when it shouldn't.
I also think it is wrong to increment SRC.H and DST.H after the inner loop because it will only have copied 256 bytes if CNT.L started out as 0.

[kennethcarvalho]

How can one get java source shown in this presentation?

[ihnwtpu]

I felt so smart when I was able to answer his question before he said the correct answer :D

[jovaha]

In most of the instructions he uses the value stack[sp] and then decrements sp or increments sp and than sets stack[sp] which would correspond to push/pop. but in the LOAD/STORE instructions he uses and sets the value stack[fp+offset]. To me that seams like something you couldn't do whit a stack. I would like to implement this whit an actual stack like data structure. Is there any way of doing LOAD/STORE instructions whit only pop/push?

[alessandromeyer]

Really great! If u'd have used scala u'd have been twice as fast writing the code. :-)