autopsy: some commentary improvements
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Autopsy is a debugging tool for RETRO. This is a fresh implementation for RETRO 12 and is intended to be a useful debugging tool.
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_
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__ _ _ _| |_ ___ _ __ ___ _ _
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/ _` | | | | __/ _ \| '_ \/ __| | | |
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| (_| | |_| | || (_) | |_) \__ | |_| |
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\__,_|\__,_|\__\___/| .__/|___/\__, |
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|_| |___/
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In implementing this, I identified the core elements I wanted:
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Autopsy is a set of debugging tools for RETRO.
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- the ability to study memory
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- dumps
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- disassembly
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- the ability to edit memory
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- provided by RETRO already via fetch/store and the assembler
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- the ability to run a word in a sandbox
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- the ability to single step through a word
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- the ability to profile instruction frequency
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- the ability to watch specific variables and memory locations
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This is more ambitious than my prior debuggers. But as I intend to use RETRO 12 for years to come, it'll be a necessary and worthwhile tool.
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So some background on the internals.
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# Background
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RETRO runs on a virtual machine called Nga. The instruction set is MISC inspired, consisting of just 30 instructions:
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0 nop 7 jump 14 gt 21 and 27 ienum
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1 lit <v> 8 call 15 fetch 22 or 28 iquery
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2 dup 9 ccall 16 store 23 xor 29 iinvoke
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3 drop 10 return 17 add 24 shift
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4 swap 11 eq 18 sub 25 zret
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5 push 12 neq 19 mul 26 end
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6 pop 13 lt 20 divmod
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0 nop 10 return 20 divmod
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1 lit <v> 11 eq 21 and
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2 dup 12 neq 22 or
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3 drop 13 lt 23 xor
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4 swap 14 gt 24 shift
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5 push 15 fetch 25 zret
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6 pop 16 store 26 end
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7 jump 17 add 27 ienumerate
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8 call 18 subtract 28 iquery
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9 ccall 19 multiply 29 iinvoke
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Four instructions are packed per 32-bit memory location. The assembler allows the instructions to be specified like:
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The first two characters of each instruction name are sufficient to identify the instruction.
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Nga exposes memory as an array of 32-bit signed integers. Each memory location can store four instructions. The assembler expects the instructions to be named using their two character identifiers. E.g.,
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'lica.... i
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#100 d
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I shorten the instructions to two letter abbreviations, with '..' for 'nop' and then construct a string with all of these. This will be used to resolve names. The ?? at the end will be used for unidentified instructions.
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# Disassembly
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I use '..' for 'no(p)' and then construct a string with all of these. This will be used to resolve names. The ?? at the end will be used for unidentified instructions.
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~~~
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'..lidudrswpupojucaccreeqneltgtfestadsumudianorxoshzrenieiqii??
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'INST s:const
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~~~
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Since instructions are packed, I need to unpack them before I can run the individual instructions. I implement `unpack` for this.
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Since instructions are packed, I need to unpack them before I can run or display the individual instructions. I implement `unpack` for this.
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~~~
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{{
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@ -70,10 +66,10 @@ Now it's possible to write words to display instruction bundles. The formats are
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unpack #4 [ name-for c:put c:put ] times ;
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~~~
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So now I'm ready to write a disassembler. I'll provide an output setup like this:
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So now I'm ready to write an actual disassembler. I'll provide an output setup like this:
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address 'instructionbundle i
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address #value d [possibly reference]
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(address) 'instructionbundle i
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(address) #value d (possibly_`reference`)
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If the value corresponds to a word in the `Dictionary`, the disassembler will display a message indicating the possible name that corresponds to the value.
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@ -146,13 +142,15 @@ And now to tie it all together:
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] times drop ;
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~~~
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# Execution Trace and Single Stepper
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Ok, now on to the fun bit: execution trace and single stepping through a word.
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This entails writing an implementation of Nga in RETRO. So to start, setup space for the data and address ("return") stacks, as well as variables for the stack pointers and instruction pointer.
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~~~
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'DataStack d:create #1024 allot
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'ReturnStack d:create #1024 allot
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'DataStack d:create #128 allot
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'ReturnStack d:create #768 allot
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'SP var
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'RP var
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'IP var
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@ -212,11 +210,11 @@ With the instructions defined, populate the jump table. The order is crucial as
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~~~
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'Instructions d:create
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&i:no , &i:li , &i:du , &i:dr , &i:sw , &i:pu , &i:po ,
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&i:ju , &i:ca , &i:cc , &i:re , &i:eq , &i:ne , &i:lt ,
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&i:gt , &i:fe , &i:st , &i:ad , &i:su , &i:mu , &i:di ,
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&i:an , &i:or , &i:xo , &i:sh , &i:zr , &i:en , &i:ie ,
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&i:iq , &i:ii ,
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&i:no , &i:li , &i:du , &i:dr , &i:sw , &i:pu ,
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&i:po , &i:ju , &i:ca , &i:cc , &i:re , &i:eq ,
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&i:ne , &i:lt , &i:gt , &i:fe , &i:st , &i:ad ,
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&i:su , &i:mu , &i:di , &i:an , &i:or , &i:xo ,
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&i:sh , &i:zr , &i:en , &i:ie , &i:iq , &i:ii ,
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~~~
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With the populated table of instructions, implementing a `process-single-opcode` is easy. This will check the instruction to make sure it's valid, then call the corresponding handler in the instruction table. If not valid, this will report an error.
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@ -302,9 +300,7 @@ The `trace` will empty the step counter and display the number of steps used.
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@Steps '%n_steps_taken\n s:format s:put ;
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~~~
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==================================================
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Tests
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# Tests
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~~~
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:test
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