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Module jit
Module jit

Module jit

Module jit

Overview

The jit module has functions for tracing the LuaJIT Just-In-Time compiler’s progress, showing the byte-code or assembler output that the compiler produces, and in general providing information about what LuaJIT does with Lua code.

Index

Below is a list of all jit functions.

Note

In this document, we will use:
  • jit_dis_x64 for require('jit.dis_x64'),
  • jit_v for require('jit.v'),
  • jit_dump for require('jit.dump').
Name Use
jit_bc.dump() Print the byte code of a function
jit_dis_x86.disass() Print the i386 assembler code of a string of bytes
jit_dis_x64.disass() Print the x86-64 assembler code of a string of bytes
jit_dump.on(), jit_dump.off() Print the intermediate or machine code of the following Lua code
jit_v.on(), jit_v.off() Print a trace of LuaJIT’s progress compiling and interpreting code
jit_bc.dump(function)

Prints the byte code of a function.

Example:

tarantool> jit_bc = require('jit.bc')
---
...

tarantool> function f()
         > print("D")
         > end
---
...

tarantool> jit_bc.dump(f)
-- BYTECODE -- 0x01113163c8:1-3
0001    GGET     0   0      ; "print"
0002    KSTR     2   1      ; "D"
0003    CALL     0   1   2
0004    RET0     0   1

---
...
function f()
  print("D")
end
require('jit.bc').dump(f)

For a list of available options, read the source code of bc.lua.

jit_dis_x86.disass(string)

Prints the i386 assembler code of a string of bytes.

Example:

tarantool> -- Disassemble hexadecimal 97 which is the x86 code for xchg eax, edi
---
...

tarantool> jit_dis_x86 = require('jit.dis_x86')
---
...

tarantool> jit_dis_86.disass('\x97')
00000000  97                xchg eax, edi
---
...

For a list of available options, read the source code of dis_x86.lua.

jit_dis_x64.disass(string)

Prints the x86-64 assembler code of a string of bytes.

Example:

tarantool> -- Disassemble hexadecimal 97 which is the x86-64 code for xchg eax, edi
---
...

tarantool> jit_dis_x64 = require('jit.dis_x64')
---
...

tarantool> jit_dis_64.disass('\x97')
00000000  97                xchg eax, edi
---
...

For a list of available options, read the source code of dis_x64.lua.

jit_dump.on(option[, output file])
jit_dump.off()

Prints the intermediate or machine code of the following Lua code.

Example:

tarantool> -- Show the machine code of a Lua "for" loop
tarantool> jit_dump = require('jit.dump')
tarantool> jit_dump.on('m')
tarantool> x = 0;
tarantool> for i = 1, 1e6 do
         > x = x + i
         > end
---- TRACE 1 start 0x01047fbc38:1
---- TRACE 1 mcode 148
104c29f6b  mov dword [r14-0xed0], 0x1
104c29f76  cvttsd2si ebp, [rdx]
104c29f7a  rorx rbx, [rdx-0x10], 0x2f
104c29f81  shr rbx, 0x11
104c29f85  mov rdx, [rbx+0x10]
104c29f89  cmp dword [rdx+0x34], +0x3f
104c29f8d  jnz 0x104c1a010  ->0
104c29f93  mov rcx, [rdx+0x28]
104c29f97  mov rdi, 0xfffd8001046b3d58
104c29fa1  cmp rdi, [rcx+0x320]
104c29fa8  jnz 0x104c1a010  ->0
104c29fae  lea rax, [rcx+0x318]
104c29fb5  cmp dword [rax+0x4], 0xfff90000
104c29fbc  jnb 0x104c1a010  ->0
104c29fc2  xorps xmm7, xmm7
104c29fc5  cvtsi2sd xmm7, ebp
104c29fc9  addsd xmm7, [rax]
104c29fcd  movsd [rax], xmm7
104c29fd1  add ebp, +0x01
104c29fd4  cmp ebp, 0x000f4240
104c29fda  jg 0x104c1a014   ->1
->LOOP:
104c29fe0  xorps xmm6, xmm6
104c29fe3  cvtsi2sd xmm6, ebp
104c29fe7  addsd xmm7, xmm6
104c29feb  movsd [rax], xmm7
104c29fef  add ebp, +0x01
104c29ff2  cmp ebp, 0x000f4240
104c29ff8  jle 0x104c29fe0  ->LOOP
104c29ffa  jmp 0x104c1a01c  ->3
---- TRACE 1 stop -> loop

---
...

tarantool> print(x)
500000500000
---
...

tarantool> jit_dump.off()
---
...

For a list of available options, read the source code of dump.lua.

jit_v.on(option[, output file])
jit_v.off()

Prints a trace of LuaJIT’s progress compiling and interpreting code.

Example:

tarantool> -- Show what LuaJIT is doing for a Lua "for" loop
tarantool> jit_v = require('jit.v')
tarantool> jit_v.on()
tarantool> l = 0
tarantool> for i = 1, 1e6 do
         >     l = l + i
         > end
[TRACE   3 "for i = 1, 1e6 do
    l = l + i
end":1 loop]
---
...

tarantool> print(l)
500000500000
---
...

tarantool> jit_v.off()
---
...

For a list of available options, read the source code of v.lua.