Hi !
On Mon, May 30, 2016 at 2:39 PM, Ben Coman btc@openinworld.com wrote:
On Sun, May 29, 2016 at 10:14 AM, Ben Coman btc@openinworld.com wrote:
Hi Clement, Thanks for your detailed reply. I particularly liked your warm up exercises. Goal directed learning is better than general browsing.
On Tue, May 24, 2016 at 1:29 AM, Clément Bera bera.clement@gmail.com
wrote:
Hi Ben,
The REPL image expects chunk format. Hence you need to write "3 + 4 !"
To get warmed-up:
- Inspect the object memory, then look for the first class table page
instance variable. It's an oop referencing an array, try in the simulator to "printOop:" the address of the first class table page that you found. It should print it in the Transcript, the first entries are immediate, in Spur32 SmallInteger/Character/SmallInteger.
The inspector showed a Spur32MMLECoSimulator and classTableFirstPage held 16r5311F8. Plugging that into [print oop...] showed...
16r5311F8: a(n) Array 16r52D108 nil 16r15C3A50 class SmallInteger 16r878D70 class Character 16r15C3A50 class SmallInteger 16r1111DC0 class SmallFloat64 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r87AE60 class Array 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r52D108 nil 16r878C58 class LargeNegativeInteger 16r878C90 class LargePositiveInteger 16r10AEAE8 class BoxedFloat64 16r879438 class Message
All the nils I guess are due to the class table being a hash map?
Is there some way from within the simulation to reference an object by its hex number. For example, to use the size of that array from within the simulation, something like...
classTableSize := 16r5311F8 objectFromHex size
You got the right result. The the class table is a linked list of pages, each page being an array. The first page, shown here, is reserved for frequently used classes.
Indexes 0-15 are reserved for tagged object. Indexes 16-32 are reserved for hidden classes. Typically the class table pages are instances of Array, but the use index 16 so the VM know they are hidden. The rest is for real classes that are frequently used. There are many nils so we have free space for new features. It's not a hash map.
I don't think things like that exists: *classTableSize := 16r5311F8 objectFromHex size. *For oops debugging features are tied to printing through the simulator instance right now. However there is something like that in the JIT. In the machine code zone we can access part of the bytes as CogMethodSurrogate and its subclasses and in the stack we can do the same for stack pages with the corresponding surrogate. In this case one can do something like: CogMethodSurrogate at: 16r51578 objectMemory: objectMemory cogit: cogit And then one can ask the surrogate things like: surrogate cmRefersToYoung And it reads the correct bytes for you, in this case answering if the cog method has a reference to a young object.
- print the active stack, look for the method's address. Try to print
it as an oop, and if it tells you "address in the machine code zone", print the cog method and its machine code instead.
I presume is the active stack is [print call stack] which produces...
16r1012F8 M MultiByteFileStream(StandardFileStream)>basicNext 16r1E7408: a(n) MultiByteFileStream 16r101334 M UTF8TextConverter>nextFromStream: 16r1EA418: a(n) UTF8TextConverter 16r10135C M MultiByteFileStream>next 16r1E7408: a(n) MultiByteFileStream 16r10138C I MultiByteFileStream(PositionableStream)>nextChunkNoTag 16r1E7408: a(n) MultiByteFileStream 16r1013B0 I StdioListener>run 16r1E7C98: a(n) StdioListener 16r1013D0 I [] in UndefinedObject>(nil) 16r52D108: a(n) UndefinedObject 16r1013F0 I [] in BlockClosure>newProcess 16r1E7E00: a(n) BlockClosure
[print oop...] 16r1012F8 tells me... 16r1012F8 is in the stack zone
[print cog method for...] 16r1012F8 tells me... not a method
[print mc/cog frame] says... Assertion failed with debugger at CogVMSimulatorLSD(CoInterpreter)>>isMachineCodeFrame:
So I seem to be missing something.
I restarted the simulator and this time... [print call stack...] 16r1012F8 M MultiByteFileStream(StandardFileStream)>basicNext 16r2A1BA8: a(n) MultiByteFileStream 16r101334 M UTF8TextConverter>nextFromStream: 16r2A2188: a(n) UTF8TextConverter 16r10135C M MultiByteFileStream>next 16r2A1BA8: a(n) MultiByteFileStream 16r10138C I MultiByteFileStream(PositionableStream)>nextChunkNoTag 16r2A1BA8: a(n) MultiByteFileStream 16r1013B0 I StdioListener>run 16r2A1B00: a(n) StdioListener 16r1013D0 I [] in UndefinedObject>(nil) 16r52D108: a(n) UndefinedObject 16r1013F0 I [] in BlockClosure>newProcess 16r2A1690: a(n) BlockClosure
[print oop...] 16r1012F8 16r1012F8 is in the stack zone
[print oop...] 16r2A1BA8 16r2A1BA8: a(n) MultiByteFileStream 16r2A2740 '????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????' 16r1 =0 (16r0) 16r1 =0 (16r0) 16r52D108 nil 16r52D108 nil 16r52D118 false 16r9AA1E8 #stdin 16r24CC18 a ByteArray 16r2A2728 '?' 16r52D108 nil 16r2A2188 an UTF8TextConverter 16r6DF1D8 #lf 16r52D128 true
Now after doing 3+4! several times, [print call stack...] produces... 16r101300 M MultiByteFileStream(StandardFileStream)>basicNext 16r2A1BA8: a(n) MultiByteFileStream 16r10133C M UTF8TextConverter>nextFromStream: 16r2A2188: a(n) UTF8TextConverter 16r101364 M MultiByteFileStream>next 16r2A1BA8: a(n) MultiByteFileStream 16r10138C M MultiByteFileStream(PositionableStream)>nextChunkNoTag 16r2A1BA8: a(n) MultiByteFileStream 16r1013B0 I StdioListener>run 16r2A1B00: a(n) StdioListener 16r1013D0 I [] in UndefinedObject>(nil) 16r52D108: a(n) UndefinedObject 16r1013F0 I [] in BlockClosure>newProcess 16r2A1690: a(n) BlockClosure
btw, What is the meaning of the M and I in the second column? I notice that 16r10138C has changed from an I to a M.
Also the address associated with basicNext changed from 16r1012F8 to 16r101300. Can some meaning be inferred from that?
Some explanations are needed here :-)
The M or I at the beginning of the printing are for 'Interpreted frame' or 'Machine code frame'.
When you do [print call stack], you print the list of stack frame in the current stack. For example, 16r101300 M MultiByteFileStream(StandardFileStream)>basicNext means that: - the stack frame address in the stack zone is 16r101300 - the machine code version of the method is executed in this frame (M and not I). - the receiver has the type MultiByteFileStream - the stack frame on top of the stack is the activation for the method StandardFileStream>>basicNext
Now what you tried to do is to print the frame as a method, and that won't work (It's not obvious and my exercise was not very precised, sorry).
You can use [print frame ...] and put the frame's hex to print it. Alternatively, asyou usually want the top (a.k.a. head) frame, you can directly use [print ext head frame] if it's a machine code frame.
That should print something like that (I print a random frame here): 16r103160: arg1: 16r8239 =16668(16r411C) 16r10315C: arg2: 16r825D =16686(16r412E) 16r103158: arg3: 16r2E21C0 =a(n) Point 16r103154: arg4: 16r9BC480 =a(n) StrikeFont 16r103150: arg5: 16r1 =0(16r0) 16r10314C: caller ip: 16r564E0=353504 16r103148: saved fp: 16r103184=1061252 16r103144: method: 16r51578 16r102BDD0 16r102BDD0: a(n) CompiledMethod 16r103144: mcfrm flags: 16r0 numArgs: 6 noContext notBlock 16r103140: context: 16r52D108 nil 16r10313C: receiver: 16r2E0078 a GrafPort 16r103138: stck: 16r2E0078 a GrafPort 16r103134: stck: 16r1A115D0
Now that you've print the frame, you can see the method addresses in this line: 16r103144: method: 16r51578 16r102BDD0 16r102BDD0: a(n) CompiledMethod. This is a machine code frame, so the method has two addresses: 16r51578 => in generated method, so you need to use [disassembleMethod/trampoline...] and write down the hex to see the disassembly. (Toggle Transcript first and open a large Transcript if you do that). 16r102BDD0 => in the heap. This is the bytecode version of the method. You can print it using [print oop...]
Ok ! One last warm-up exercise:
3) When the simulator has started and the REPL window has popped up, select [single step]. Then enter something in the REPL window and execute it. Once done, do [report recent instructions]. You should be able to see in the Transcript the last 100 machine instruction with the register state in-between each instruction.
I think I should write down those exercise as a blog post...
cheers -ben