Lua virtual machine in Rust, why the heck not.
_
commit
b07de4810d
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/target
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/untracked
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# This file is automatically @generated by Cargo.
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# It is not intended for manual editing.
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version = 3
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[[package]]
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name = "lua_why_not"
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version = "0.1.0"
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[package]
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name = "lua_why_not"
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version = "0.1.0"
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edition = "2021"
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# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
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[dependencies]
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Lua source code
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`hello.lua`
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```lua
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print "Hello."
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```
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`math.lua`
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```lua
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local function add (a, b)
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return a + b
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end
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print (("1 + 2 = %i"):format (add (1, 2)))
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```
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luac5.4 listing
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```
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main <hello.lua:0,0> (5 instructions at 0x564f4fd74cc0)
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0+ params, 2 slots, 1 upvalue, 0 locals, 2 constants, 0 functions
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1 [1] VARARGPREP 0
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2 [1] GETTABUP 0 0 0 ; _ENV "print"
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3 [1] LOADK 1 1 ; "Hello."
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4 [1] CALL 0 2 1 ; 1 in 0 out
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5 [1] RETURN 0 1 1 ; 0 out
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```
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```
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main <math.lua:0,0> (12 instructions at 0x55ee2417acc0)
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0+ params, 7 slots, 1 upvalue, 1 local, 3 constants, 1 function
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1 [1] VARARGPREP 0
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2 [3] CLOSURE 0 0 ; 0x55ee2417b000
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3 [5] GETTABUP 1 0 0 ; _ENV "print"
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4 [5] LOADK 2 1 ; "1 + 2 = %i"
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5 [5] SELF 2 2 2k ; "format"
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6 [5] MOVE 4 0
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7 [5] LOADI 5 1
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8 [5] LOADI 6 2
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9 [5] CALL 4 3 0 ; 2 in all out
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10 [5] CALL 2 0 0 ; all in all out
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11 [5] CALL 1 0 1 ; all in 0 out
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12 [5] RETURN 1 1 1 ; 0 out
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function <math.lua:1,3> (4 instructions at 0x55ee2417b000)
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2 params, 3 slots, 0 upvalues, 2 locals, 0 constants, 0 functions
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1 [2] ADD 2 0 1
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2 [2] MMBIN 0 1 6 ; __add
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3 [2] RETURN1 2
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4 [3] RETURN0
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```
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```
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main <test_vectors/is_93.lua:0,0> (14 instructions at 0x559f55e1ecd0)
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0+ params, 2 slots, 1 upvalue, 1 local, 5 constants, 1 function
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1 [1] VARARGPREP 0
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2 [1] GETTABUP 0 0 0 ; _ENV "arg"
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3 [1] GETI 0 0 1
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4 [1] EQK 0 1 0 ; "93"
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5 [1] JMP 4 ; to 10
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6 [2] GETTABUP 0 0 2 ; _ENV "print"
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7 [2] LOADK 1 3 ; "it's 93"
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8 [2] CALL 0 2 1 ; 1 in 0 out
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9 [2] JMP 3 ; to 13
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10 [4] GETTABUP 0 0 2 ; _ENV "print"
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11 [4] LOADK 1 4 ; "it's not 93"
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12 [4] CALL 0 2 1 ; 1 in 0 out
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13 [9] CLOSURE 0 0 ; 0x559f55e1f3d0
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14 [9] RETURN 1 1 1 ; 0 out
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constants (5) for 0x559f55e1ecd0:
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0 S "arg"
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1 S "93"
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2 S "print"
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3 S "it's 93"
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4 S "it's not 93"
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locals (1) for 0x559f55e1ecd0:
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0 unused_fn 14 15
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upvalues (1) for 0x559f55e1ecd0:
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0 _ENV 1 0
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function <test_vectors/is_93.lua:7,9> (4 instructions at 0x559f55e1f3d0)
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0 params, 2 slots, 1 upvalue, 0 locals, 2 constants, 0 functions
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1 [8] GETTABUP 0 0 0 ; _ENV "print"
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2 [8] LOADK 1 1 ; "unused"
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3 [8] CALL 0 2 1 ; 1 in 0 out
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4 [9] RETURN0
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constants (2) for 0x559f55e1f3d0:
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0 S "print"
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1 S "unused"
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locals (0) for 0x559f55e1f3d0:
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upvalues (1) for 0x559f55e1f3d0:
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0 _ENV 0 0
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```
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Octal dump of luac5.4 byte code
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```
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0000000 1b 4c 75 61 54 00 19 93 0d 0a 1a 0a 04 08 08 78 >.LuaT..........x<
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0000020 56 00 00 00 00 00 00 00 00 00 00 00 28 77 40 01 >V...........(w@.<
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0000040 8b 40 68 65 6c 6c 6f 2e 6c 75 61 80 80 00 01 02 >.@hello.lua.....<
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0000060 85 51 00 00 00 0b 00 00 00 83 80 00 00 44 00 02 >.Q...........D..<
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0000100 01 46 00 01 01 82 04 86 70 72 69 6e 74 04 87 48 >.F......print..H<
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0000120 65 6c 6c 6f 2e 81 01 00 00 80 85 01 00 00 00 00 >ello............<
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0000140 80 80 81 85 5f 45 4e 56 >...._ENV<
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0000150
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```
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```
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0000000 1b 4c 75 61 54 00 19 93 0d 0a 1a 0a 04 08 08 78 >.LuaT..........x<
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0000020 56 00 00 00 00 00 00 00 00 00 00 00 28 77 40 01 >V...........(w@.<
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0000040 8a 40 6d 61 74 68 2e 6c 75 61 80 80 00 01 07 8c >.@math.lua......<
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0000060 51 00 00 00 4f 00 00 00 8b 00 00 00 03 81 00 00 >Q...O...........<
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0000100 14 81 02 02 00 02 00 00 81 02 00 80 01 83 00 80 >................<
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0000120 44 02 03 00 44 01 00 00 c4 00 00 01 c6 00 01 01 >D...D...........<
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0000140 83 04 86 70 72 69 6e 74 04 8b 31 20 2b 20 32 20 >...print..1 + 2 <
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0000160 3d 20 25 69 04 87 66 6f 72 6d 61 74 81 01 00 00 >= %i..format....<
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0000200 81 80 81 83 02 00 03 84 22 01 00 01 2e 00 01 06 >........".......<
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0000220 48 01 02 00 47 01 01 00 80 80 80 84 01 00 00 01 >H...G...........<
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0000240 80 82 82 61 80 84 82 62 80 84 80 8c 01 02 02 00 >...a...b........<
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0000260 00 00 00 00 00 00 00 00 80 81 84 61 64 64 82 8c >...........add..<
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0000300 81 85 5f 45 4e 56 >.._ENV<
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0000306
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```
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# Interpretation of byte code
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Overall structure
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- Roughly 32 byte header with magic number, version number, etc.
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- File name
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- `80 80 00 01 02 85` header for main function
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- Packed 4-byte instructions for main function
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- `82` or `83` length prefix for string table
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- String table for main function
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- `81 01 00 00 81 80 81 83 02 00 03 84` header for "add" function
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- Packed 4-byte instructions for "add" function
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- `80 80 80 84 01 00 00 01 80` Header for file-scope debug symbols?
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- File-scope debug symbols?
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- String table for entire file?
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## Bytecodes
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Per lopcodes.h, instructions are 32 bits long, always.
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The opcode is encoded in the first (highest?) 7 bits.
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```
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83 80 00 00 ; 0x03 = 3 = LOADK
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0b 00 00 00 ; 0x0b = 11 = GETTABUP
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22 01 00 01 ; 0x22 = 34 = ADD
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2e 00 01 06 ; 0x2e = 46 = MMBIN
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c4 00 00 01 ; 0xc4 = 68 = CALL
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44 00 02 01 ; 0x44 = 68 = CALL
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46 00 01 01 ; 0x46 = 70 = RETURN
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47 01 01 00 ; 0x47 = 71 = RETURN0
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48 01 02 00 ; 0x48 = 72 = RETURN1
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51 00 00 00 ; 0x51 = 81 = VARARGPREP
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```
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## Strings
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Filenames are encoded at the top, and there's a string table at the bottom.
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Strings appear to be prefixed with a variable-length length prefix.
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There is an extra byte before each string which I can't account for,
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and the lengths seem to be off by one, e.g. 0x84 is a length of 3, not 4.
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| --- |
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| "add" | 81 84 61 64 64
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| "_ENV" | 81 85 5f 45 4e 56
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| "print" | 04 86 70 72 69 6e 74
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| "format" | 04 87 66 6f 72 6d 61 74
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| "@math.lua" | 01 8a 40 6d 61 74 68 2e 6c 75 61
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| "1 + 2 = %i" | 04 8b 31 20 2b 20 32 20 3d 20 25 69
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enum Instruction {
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VarArgPrep (i32),
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GetTabUp (u8, u8, u8),
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GetI (u8, u8, u8),
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EqK (u8, u8, u8),
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Jmp (i32),
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LoadK (u8, i32),
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Call (u8, u8, u8),
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Closure (u8, i32),
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Return (u8, u8, u8),
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}
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#[derive (Clone, Debug, PartialEq)]
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enum Value {
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Nil,
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False,
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True,
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Float (f64),
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String (String),
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// These are all bogus, I haven't figured out how to implement
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// tables and function pointers yet
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BogusArg,
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BogusPrint,
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}
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impl Default for Value {
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fn default () -> Self {
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Self::Nil
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}
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}
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impl From <String> for Value {
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fn from (x: String) -> Self {
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Self::String (x)
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}
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}
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impl From <&str> for Value {
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fn from (x: &str) -> Self {
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Self::from (String::from (x))
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}
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}
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struct Chunk {
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instructions: Vec <Instruction>,
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constants: Vec <Value>,
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}
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fn main() {
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let arg: Vec <_> = std::env::args ().collect ();
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let chunk = Chunk {
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instructions: vec! [
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Instruction::VarArgPrep (0),
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Instruction::GetTabUp (0, 0, 0),
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Instruction::GetI (0, 0, 1),
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Instruction::EqK (0, 1, 0),
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Instruction::Jmp (4),
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Instruction::GetTabUp (0, 0, 2),
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Instruction::LoadK (1, 3),
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Instruction::Call (0, 2, 1),
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Instruction::Jmp (3),
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Instruction::GetTabUp (0, 0, 2),
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Instruction::LoadK (1, 4),
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Instruction::Call (0, 2, 1),
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Instruction::Return (1, 1, 1),
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],
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constants: vec! [
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"arg",
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"93",
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"print",
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"it's 93",
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"it's not 93",
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].into_iter ().map (|s| Value::from (s)).collect (),
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};
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let mut registers = vec! [Value::default (); 256];
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let mut program_counter = 0i32;
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let max_iters = 2000;
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for _ in 0..max_iters {
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let instruction = chunk.instructions.get (usize::try_from (program_counter).unwrap ()).unwrap ();
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let r = &mut registers;
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let k = &chunk.constants;
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match instruction {
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Instruction::Call (a, b, c) => {
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// Take arguments from registers [a + 1, a + b)
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// Call the function in register [a]
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// Return values in registers [a, a + c - 1)
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//
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// That is, call a with b - 1 arguments and expect c returns
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//
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// e.g. CALL 0 2 1 mean "Call 0 with 1 argument, return 1 value", like for printing a constant
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// TODO: Only implement printing constants for now
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let a = usize::try_from (*a).unwrap ();
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assert_eq! (*b, 2);
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assert_eq! (*c, 1);
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println! ("{:?}", r [a + 1]);
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},
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Instruction::EqK (a, b, c_k) => {
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let a = usize::try_from (*a).unwrap ();
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let b = usize::try_from (*b).unwrap ();
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let equal = r [a] == k [b];
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match (equal, c_k) {
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(true, 0) => program_counter += 1,
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(false, 1) => program_counter += 1,
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_ => (),
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}
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},
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Instruction::GetTabUp (a, b, c) => {
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let a = usize::try_from (*a).unwrap ();
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let b = usize::try_from (*b).unwrap ();
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let c = usize::try_from (*c).unwrap ();
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// Only supported upvalue is `_ENV`
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assert_eq! (b, 0);
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let key = k.get (c).unwrap ();
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let value = match key {
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Value::String (s) => match s.as_str() {
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"arg" => Value::BogusArg,
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"print" => Value::BogusPrint,
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_ => panic! ("key not in _ENV upvalue"),
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},
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_ => unimplemented!(),
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};
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r [a] = value;
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},
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Instruction::GetI (a, b, c) => {
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let a = usize::try_from (*a).unwrap ();
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let b = usize::try_from (*b).unwrap ();
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let c = usize::try_from (*c).unwrap ();
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let table = r.get (b).unwrap ();
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let value = match table {
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Value::BogusArg => arg.get (c).unwrap ().as_str().into (),
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_ => unimplemented!(),
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};
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r [a] = value;
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},
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Instruction::Jmp (sJ) => program_counter += sJ,
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Instruction::LoadK (a, bx) => {
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let a = usize::try_from (*a).unwrap ();
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let bx = usize::try_from (*bx).unwrap ();
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r [a] = k [bx].clone ();
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},
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Instruction::Return (_a, _b, _c) => {
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break;
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},
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Instruction::VarArgPrep (_) => (),
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_ => (),
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}
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program_counter += 1;
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}
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}
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Binary file not shown.
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@ -0,0 +1,15 @@
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-- Put some very long comment here so the error will
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-- have an interesting line number in the traceback
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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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--
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--
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--
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--
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--
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error ("bogus")
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Binary file not shown.
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@ -0,0 +1 @@
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print "Hello."
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Binary file not shown.
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@ -0,0 +1,9 @@
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if arg [1] == "93" then
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print "it's 93"
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else
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print "it's not 93"
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end
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local function unused_fn ()
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print "unused"
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end
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Binary file not shown.
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@ -0,0 +1 @@
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return 0
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Binary file not shown.
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@ -0,0 +1,5 @@
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local function add (a, b)
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return a + b
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end
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print (("1 + 2 = %i"):format (add (1, 2)))
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Binary file not shown.
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@ -0,0 +1,9 @@
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local function add (a, b)
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return a + b
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end
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local function sub (a, b)
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return a - b
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end
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print (("1 + 2 = %i"):format (add (1, 2)))
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Binary file not shown.
Loading…
Reference in New Issue