1. Metasepi team meeting #6:
"Snatch-driven development"
"Snatch-driven
Kiwamu Okabe

2. Who am I?
☆ http://www.masterq.net/
☆ Twitter: @master_q
☆ Organizer of Metasepi project
☆ A developer of Ajhc Haskell compiler
☆ A Debian Maintainer
☆ 10 years' experience in developing
OS using NetBSD.

3. Agenda
☆ [1] Demo
☆ [2] What is Ajhc?
☆ [3] What is Metasepi?
☆ [4] What is compiler to build OS
☆ [5] How to use Ajhc
☆ [6] Case study: Snatch Android
☆ [7] Detail of Snatch process

4. [1] Demo
☆ RSS reader running on mbed (ARM).
☆ Show reddit articles on LCD display.
☆ You can watch the movie following.
http://bit.ly/mbedmov

5. Demo hardware
Architecture: ARM Cortex-M3
RAM size: 64kB
IO: Ethernet, LED, LCD, SD Card, USB
host/device, Serial

6. Demo software
github.com/ajhc/demo-cortex-m3

7. Demo source code
demo-cortex-m3
`-- mbed-nxp-lpc1768
|-- BuildShell
|-- build
|
`-- mbed.ld
|-- external
|
`-- mbed
|
`-- LPC1768
|
`-- GCC_ARM
|
`-- libmbed.a
|-- linux_install
|-- samples
|
`-- Haskell_Http
|
|-- EthernetInterface
|
|-- c_extern.h
|
|-- dummy4jhc.c
|
|-- hs_src
|
|
`-- *.hs
|
|-- main.c
|
`-- mbed-rtos
`-- src
`-- gcc4mbed.c
<= Compile enviroment
<= Linker Sscript
<= mbed library (compiled)
<= TCP/IP protocol stack
<= C lanuage stub for Haskell
<=
<=
<=
Haskell source code
C language main function
mbed-rtos OS

8. [2] What is Ajhc?
http://ajhc.metasepi.org/
☆ Ajhc := A fork of jhc
☆ jhc := John's Haskell Compiler
☆ http://repetae.net/computer/jhc/
☆ Jhc outputs binary that has lowmemory-footprint and runs fast.
☆ Good for embedded software.

9. Why need Ajhc?
☆ GHC is de facto standard on Haskell.
☆ GHC := Glasgow Haskell Compiler
☆ http://www.haskell.org/ghc/
☆ Why need another Haskell compiler?
☆ To develop kernel named "Metasepi".

10. [3] What is Metasepi?
http://metasepi.org/
☆ Unix-like OS designed by strong type.
☆ Using ML or more strong type lang.
Haskell http://www.haskell.org/
OCaml http://caml.inria.fr/
MLton http://mlton.org/
. . . and suchlike.

11. Why need Metasepi?
☆ We have already Linux or Windows.
☆ But the developers are suffering.
☆ If use the kernel changed by you,
☆ you will get many runtime error.
☆ Difficult even to reproduce it.

12. Doesn't OSS have good quality?
☆ "The Cathedral and the Bazaar"
☆ "Given enough eyeballs, all bugs are
shallow."
http://cruel.org/freeware/cathedral.html
☆ But if you develop your own product
reusing OSS...

13. Low quality out of OSS umbrella

14. Type safety
☆ Less runtime errors.
☆ "数理科学的バグ撲滅方法論のすすめ"
http://itpro.nikkeibp.co.jp/article/COLUMN/20060915/248230/

15. Kernel desperately wants type
☆ Kernels are developed with C lang.
☆ Error on user space => SEGV
☆ Error on kernel space => halt!
☆ Should design kernel with the
greatest care.
☆ C language is safe?

16. [4] What is compiler to build OS
☆ Need strong type.
☆ Need flexibility such as C language.
☆ Create it if there are not!
☆ From scratch? No thank you...
☆ Look for our compiler base.

17. Want POSIX free compiler
Programs to print "hoge" on terminal.
Measurement value is smaller,
dependence on POSIX is small.

18. Jhc output has only 20 undef
$ nm hs.out | grep
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
U
"U "
_IO_putc@@GLIBC_2.2.5
__libc_start_main@@GLIBC_2.2.5
_setjmp@@GLIBC_2.2.5
abort@@GLIBC_2.2.5
ctime@@GLIBC_2.2.5
exit@@GLIBC_2.2.5
fflush@@GLIBC_2.2.5
fprintf@@GLIBC_2.2.5
fputc@@GLIBC_2.2.5
fputs@@GLIBC_2.2.5
free@@GLIBC_2.2.5
fwrite@@GLIBC_2.2.5
getenv@@GLIBC_2.2.5
malloc@@GLIBC_2.2.5
memset@@GLIBC_2.2.5
posix_memalign@@GLIBC_2.2.5
realloc@@GLIBC_2.2.5
setlocale@@GLIBC_2.2.5
sysconf@@GLIBC_2.2.5
times@@GLIBC_2.2.5

19. Jhc is translator to C language

20. Easy to cross build

21. Survive burning out
Let's develop in dogfooding style. (The
method is called "Snatch".)

22. [5] How to use Ajhc
Case of Ubuntu 12.04 amd64.
$ sudo apt-get install haskell-platform libncurses5-dev gcc m4
$ cabal update
$ export PATH=$HOME/.cabal/bin/:$PATH
$ cabal install ajhc
$ which ajhc
/home/USER/.cabal/bin/ajhc
$ echo 'main = print "hoge"' > Hoge.hs
$ ajhc Hoge.hs
$ ./hs.out
"hoge"
You can use on Windows or Mac OS X.

23. Detail of usage
Please read "Ajhc User's Manual".
☆ ajhc.metasepi.org/manual.html
Also you can read in Japanese.
☆ ajhc.metasepi.org/manual_ja.html

24. [6] Case study: Snatch Android
Let's snatch sample app "native-activity".
developer.android.com/tools/sdk/ndk/

25. Snatch plan

26. [7] Detail of Snatch method
Let's watch Snatch animation on
Android NDK Apps. Have popcorn?
If you want to know more detail, try the
following.
$
$
$
git clone https://github.com/ajhc/demo-android-ndk.git
cd demo-android-ndk
git log -p

27. Step0: Before Snatch
// ### native-activity/jni/main.c ###
struct saved_state {
// --snip-struct engine {
// --snip-static int engine_init_display(struct engine* engine) {
// --snip-static void engine_draw_frame(struct engine* engine) {
// --snip-static void engine_term_display(struct engine* engine) {
// --snip-static int32_t engine_handle_input(struct android_app* app,
AInputEvent* event) {
// --snip-static void engine_handle_cmd(struct android_app* app, int32_t
cmd) {
// --snip-void android_main(struct android_app* state) {
// --snip--

28. Step1: Call Haskell empty code
-- ### native-activity/hs_src/Main.hs ###
main :: IO ()
main = return ()
// ### native-activity/jni/main.c ###
void android_main(struct android_app* state) {
// --snip-{ // Run Haskell code.
int hsargc = 1;
char *hsargv = "q";
char **hsargvp = &hsargv;
hs_init(&hsargc, &hsargvp);
_amain();
hs_exit();
}
// --snip--

29. Step2: struct => Storable (cont.)
-- ### native-activity/hs_src/AndroidNdk.hs ###
{-# LANGUAGE ForeignFunctionInterface #-}
module AndroidNdk where
import Foreign.Storable
import Foreign.C.Types
import Foreign.Ptr
foreign import primitive "const.sizeof(struct saved_state)"
sizeOf_SavedState :: Int
foreign import primitive "const.offsetof(struct saved_state,
angle)" offsetOf_SavedState_angle :: Int
foreign import primitive "const.offsetof(struct saved_state,
offsetOf_SavedState_x :: Int
foreign import primitive "const.offsetof(struct saved_state,
offsetOf_SavedState_y :: Int
data SavedState = SavedState { sStateAngle :: Float
, sStateX
:: Int
, sStateY
:: Int }
x)"
y)"

30. Step2: struct => Storable
instance Storable SavedState where
sizeOf
= const sizeOf_SavedState
alignment = sizeOf
poke p sstat = do
pokeByteOff p offsetOf_SavedState_angle $ sStateAngle sstat
pokeByteOff p offsetOf_SavedState_x
$ sStateX sstat
pokeByteOff p offsetOf_SavedState_y
$ sStateY sstat
peek p = do
angle <- peekByteOff p offsetOf_SavedState_angle
x
<- peekByteOff p offsetOf_SavedState_x
y
<- peekByteOff p offsetOf_SavedState_y
return $ SavedState { sStateAngle = angle, sStateX = x,
sStateY = y }
-- snip --
// ### native-activity/jni/c_extern.h ###
struct saved_state {
float angle;
int32_t x;
int32_t y;
};

31. Step3: Snatch 1st func (cont.)
-- ### native-activity/hs_src/AndroidNdk.hs ###
newtype {-# CTYPE "AInputEvent" #-} AInputEvent = AInputEvent ()
foreign import primitive "const.AINPUT_EVENT_TYPE_MOTION"
c_AINPUT_EVENT_TYPE_MOTION :: Int
foreign import ccall "c_extern.h AInputEvent_getType"
c_AInputEvent_getType :: Ptr AInputEvent -> IO Int
foreign import ccall "c_extern.h AMotionEvent_getX"
c_AMotionEvent_getX :: Ptr AInputEvent -> CSize -> IO Float
foreign import ccall "c_extern.h AMotionEvent_getY"
c_AMotionEvent_getY :: Ptr AInputEvent -> CSize -> IO Float
engineHandleInput :: Ptr AndroidEngine -> Ptr AInputEvent -> IO Int
engineHandleInput eng event = do
t <- c_AInputEvent_getType event
if t /= c_AINPUT_EVENT_TYPE_MOTION then return 0
else do enghs <- peek eng
let stat = engState enghs
x <- c_AMotionEvent_getX event 0
y <- c_AMotionEvent_getY event 0
let enghs' = enghs { engAnimating = 1, engState = stat
{ sStateX = truncate x, sStateY = truncate y } }
poke eng enghs'
return 1

32. Step3: Snatch 1st func
// ### native-activity/jni/main.c ###
extern int32_t engineHandleInput(struct engine* engine,
AInputEvent* event); // Haskell impl
static int32_t engine_handle_input(struct android_app* app,
AInputEvent* event) {
struct engine* engine = (struct engine*)app->userData;
return engineHandleInput(engine, event);
}

33. Step4: Snatch 2nd func (cont.)
-- ### native-activity/hs_src/AndroidNdk.hs ###
foreign import primitive "const.APP_CMD_SAVE_STATE"
c_APP_CMD_SAVE_STATE :: Int
-- snip -foreign import ccall "c_extern.h engine_init_display"
c_engine_init_display :: Ptr AndroidEngine -> IO Int
foreign import ccall "c_extern.h engine_draw_frame"
c_engine_draw_frame :: Ptr AndroidEngine -> IO ()
-- snip -foreign import ccall "c_extern.h ASensorEventQueue_disableSensor"
c_ASensorEventQueue_disableSensor :: Ptr ASensorEventQueue -> Ptr
ASensor -> IO Int
engineHandleCmd :: Ptr AndroidEngine
engineHandleCmd eng cmd
| cmd == c_APP_CMD_SAVE_STATE = do
-- snip --
-> Int -> IO ()
enghs <- peek eng
let app = engApp enghs
apphs <- peek app
sstat <- malloc
poke sstat $ engState enghs

34. Step4: Snatch 2nd func
// ### native-activity/jni/c_extern.h ###
int engine_init_display(struct engine* engine);
void engine_draw_frame(struct engine* engine);
void engine_term_display(struct engine* engine);
// ### native-activity/jni/main.c ###
extern void engineHandleCmd(struct engine* engine, int32_t cmd);
static void engine_handle_cmd(struct
cmd) {
struct engine* engine = (struct
engineHandleCmd(engine, cmd);
}
android_app* app, int32_t
engine*)app->userData;

35. Step5: Snatch remaining funcs
Snatch the following functions.
☆ engine_init_display()
☆ engine_draw_frame()
☆ engine_term_display()

36. Step6: Snatch main func (cont.)
-- ### native-activity/hs_src/Main.hs ###
main :: IO () -- Dummy
main = return ()
foreign export ccall "androidMain" androidMain :: Ptr AndroidApp > IO ()
androidMain :: Ptr AndroidApp -> IO () -- True main
androidMain app = do
eng <- malloc
poke eng defaultAndroidEngine
apphs <- peek app
let apphs' = apphs { appUserData = eng, appOnAppCmd =
p_engineHandleCmd , appOnInputEvent = p_engineHandleInput }
poke app apphs'
enghs <- peek eng
-- Prepare to monitor accelerometer
sManage <- c_ASensorManager_getInstance
accel <- c_ASensorManager_getDefaultSensor sManage
c_ASENSOR_TYPE_ACCELEROMETER
let looper = appLooper apphs'
when (ss_p /= nullPtr) $ do
ss <- peek ss_p
-- snip --

37. Step6: Snatch main func
// ### native-activity/jni/main.c ###
void android_main(struct android_app*
app_dummy(); // Make sure glue
// Init & run Haskell code.
int hsargc = 1;
char *hsargv = "q";
char **hsargvp = &hsargv;
}
hs_init(&hsargc, &hsargvp);
androidMain(state);
hs_exit();
state) {
isn't stripped.

38. Step7: Get clear => GOAL
We are in the strong typed world.
Haskell's turn, now!

39. PR: Call For Articles
☆ http://www.paraiso-lang.org/ikmsm/
☆ Fanzine of functional programming.
☆ About Haskell or OCaml or . . .
☆ Article about Ajhc in C84 book.
☆ Call me if you read it!
http://www.paraiso-lang.org/ikmsm/books/c85.html