Writing mruby debugger

Yurie YamaneMasayoshi Takahashi

(Team Yamanekko)

2014/11/18 RubyConf 2014

Outline● Who are we?● Why debugger?● What's debugger?● Demo● How mruby and debugger works● Debugger UI (Eclipse plugin)● Conclusion and Future works

!!! Notice !!!● Technical talk

● including GDB and Eclipse● less Ruby● not fluent C, Java, English● not finished yet

About us● Yurie Yamane● Masayoshi Takahashi

Yamanekko

http://mrb.h2so5.net/

Tatsu-zine Publishing

Why Debugger?

Why debugger?CRuby programmers are not sofamiliar with debugger

irb / pry are your friend

But we think mruby programmersneed debugger→ Why?

What we had talked

https://www.flickr.com/photos/igaiga/10836637785/

http://www.flickr.com/photos/igaiga/8564676738/

Tools we use now● C● Java

● making our Eclipse Plugin● hacking Eclipse/CDT

● GDB● (a little Ruby)

https://www.gnu.org/software/gdb/mascot/

https://gcc.gnu.org/

http://www.eclipse.org/artwork/

https://www.ruby-lang.org/en/about/logo/

Why we need mrubydebugger

● targets of mruby● application embedded

● apache / nginx● redis

● microcontroller● RTOS● bare metal

Why we need mrubydebugger

*.rb

*.c *.rb

bin/ruby

libruby.a

CRuby

mruby

(Your code)

debugging mruby

C Ruby

(out of focus)

GDB ???

mruby

libruby.a

mruby sample code

CRuby debugger● ruby-debug

● < Ruby 2.0● byebug

● >= Ruby 2.0

porting them to mruby isthe answer?

partially, yes

→ we need another solution

C Ruby

Our approachmruby debugger on GDB

mruby application

GDB

Front-end

mruby Debugger

Pros && Cons● Pros

● support C and Ruby● easy to develop

● on the shoulders of giants

● Cons● need GDB, not standalone● a little complicated

What's Debugger?

Functions of debugger● Control Execution

● breakpoint● step into / step over / continue

● Show Variables● Show Stacktraces

Functions of debugger● Control Execution

● breakpoint● step into / step over / continue

● Show Variables● Show Stacktraces

today's topics

total picture● Eclipse CDT (as frontend)● our library● GDB

● GDB/MI protocol● mrubyVM (libmruby.a)

total picture

mruby app (bytecode)

GDB

Eclipse CDT

mruby debugger (C)

mruby Debugger (plugin)

mrubyVM (libmruby.a)

GDB/MI

Demo

How mruby Works

Control execution● What we want to do is:

● Suspend execution● Resume execution● show internal status

● We should know how mrubyVMworks

GDB Missing Manual

● GDB/MI● Conditional Breakpoint● Calling Program Functions

GDB Missing Manual

● GDB/MI● Conditional Breakpoint● Calling Program Functions

GDB/MI● Machine Interface protocol

● not for humans● easy to parse

● Eclipse/CDT uses thisGDB command GDB/MI command

run -exec-run

show args -exec-show-arguments

info frame -stack-info-frame

GDB/MI

GDB Missing Manual

● GDB/MI● Conditional Breakpoint● Calling Program Functions

Conditional Breakpointadd conditions to breakpoint

normal breakpoint

conditional breakpoint

GDB Missing Manual

● GDB/MI● Conditional Breakpoint● Calling Program Functions

Call function from GDB● GDB can execute C function

● GDB can get return value● CLI: call / print command● GDB/MI: -data-evaluate-expression

How mrubyVM works● like Instruction pipeline steps

Fetch

Decode

Execute

Write(update status)

How mrubyVM works● use CODE_FETCH_HOOK

Fetch

Decode

Execute

Write(update status)

CODE_FETCH_HOOK

CODE_FETCH_HOOK● hook function for debuging● execute after FETCH with each

cycle● when #define ENABLE_DEBUG only

CODE_FETCH_HOOK

src/vm.c

code_fetch_hook

include/mruby.h

ENABLE_DEBUG

include/mrbconf.h

How mrubyVM works● check status at C_F_HOOK

Fetch

Decode

CODE_FETCH_HOOK set a breakpoint here

our code_fetch_hook

set a breakpoint here

Breakpoint: Ruby → C

breakpoint: foo.rb:12Ruby

Cbreakpoint: ???: ???

Breakpoint: Ruby → C

breakpoint: foo.rb:12Ruby

C breakpoint: hoge.c: 116 if line == 12 && filaname == “foo.rb”

condition

mrbc: mruby compiler● mrubyVM uses bytecode● bin/mrbc is bytecode compiler

● only compile; do not execute● mrbc -g option

● “-g produce debugging information”● store source filename and line

number to debug

1 source line != 1 bytecode

v = 2

num = 1

num = v + num

OP_LOADI R1 2 ; R1:v

OP_LOADI R2 1 ; R2:num

OP_MOVE R6 R1OP_MOVE R7 R2OP_ADD R6 :+ 1OP_MOVE R2 R6

source code bytecode

1 source line != 1 bytecodeSolution

save previous filename andline number

if same line in same file,ignore (do not stop)

Show Variables● calling C function from GDB● add new functions

● getlocals(mrb): return list of localvars● getlocalValue(mrb, sym): return a localvar

● never called by mruby itself● called by GDB only

Debugger UI

Eclipse● Eclipse supports C programming

● CDT● DSF and DSF-GDB (with GDB/MI)

Eclipse

Eclipse Platform

DSF-GDBDSFC

DT

mruby debugger plugin

debug.uidebug.core

Eclipse CDT● C/C++ Development Tooling● Parser, Indexer, Editor, Builder, …● Using Eclipse standard

packages/frameworks● Debugger: Eclipse Debug

Framework

DSF / DSF-GDB● Debugger Service Framework● new framework of CDT● more flexible than old framework

(CDI)● DSF-GDB: GDB debugger using DSF● we use/modify DSF-GDB

Eclipse mruby debugger

Breakpoint Managerfor mruby

mruby editor(experimental)

mruby variable view GDB Adapterfor mruby

……

mruby Variable View

mruby Editor

mruby BreakpointMarker

Marker on *.rb →breakpoint on *.c

linenum: 12path: foo.rb

Marker

foo.rb *.c

CODE_FETCH_HOOK breakpoint

line == 12 &&md_strcmp(filename, “foo.rb”)

Condition

Breakpoint Manager

mrubyBreakpoint Manager GDB

Breakpoint Manager GDB

C

Ruby

linenum: 12path: foo.rb

Marker

linenum: 12path: foo.c

Marker

break foo.c:12

break XXX.c:YYYif line ==12 && path == “foo.rb”

mruby Variable View show Name, Type and Value ofvariables

mruby Variable View hilighting updated values

get list of variables

C

Ruby

Eclipse

mruby app

GDB

Eclipse GDB

“info locals”

“call getlocals(mrb)” exec getlocals()

return locals (as string)return locals

return locals

get variable info● get a list of local variables

command

GDB CLI info locals

GDB/MI -stack-list-locals

mruby -data-evaluate-expression getlocals

variable list format

321,018 25-data-evaluate-expression getlocals(mrb)

321,040 25^done,value=”0x10008c640 \”locals=[{name=\\\”v\\\”,value=\\\”2\\\”,type=\\\”Fixnum\\\”},{name=\\\”num\\\”,value=\\\”1\\\”,type=\\\”Fixnum\\\”},...

-stack-list-locals 1^done,locals=[{name="i",value="0"},{name="k",value="1"}]

for C:

for mruby (command):

for mruby (result):

get variable info● get a value of variable by name

command

GDB CLI print foo

GDB/MI (using variable object; -var-***)

mruby -data-evaluate-expression getlocalvalue

Start mruby Debugger

Stop at Breakpoint

Show Variables ● org

● Breakpoint marker filename,line● break

● mruby variable view● GDB Adapter for mruby● ...

update value of num

Change Type of v

Symbol and Hash

Show arguments ● get local variables● ...

create new object● get local variables● ...

call RubyConf#prev● get local variables● ...

console

Conclusion

Conclusion● mruby debugger on GDB

● breakpoints on *.rb● execution control● show variables

Future Works● mruby stacktrace view● making mrbgem● support step execution● support instance variables &&

class variables

Thank you!