This document discusses the operating system architecture and system calls of the Tock operating system. It describes the key components of Tock including processes, system calls like command, subscribe, yield, and allow, and the driver API. Processes in Tock are isolated and protected with memory protection units. System calls allow processes to interact with drivers to perform actions or register callbacks. Drivers implement the SyscallDriver trait to handle system calls.

1. Systèmes
d'exploitation
Pilots Tock

2. Ron Rivest
• Américain
• Stanford
• MIT
• Inventeur RSA
2

3. Contenu
• L'architecture
• Appels système
• API du pilote Syscall
3

4. Bibliographie pour aujourd'hui
• A. Radovici, I. Culic, Getting Started with
Secure Embedded Systems
– Chapitre 3, 7, 8
4

5. TOCK
5

6. Pile du système d'exploitation

7. Application (Process)
• Exécutable autonome
– compilé sans noyau Tock
• Protection de la mémoire
– Régions MPU
• Peut (seg)fault
• Code relocalisable
– où le compilateur le
permet
• IPC
– découverte de services

8. APPELS SYSTÈME
8

9. Appels système de Tock 2.0
• Yield (0)
• Subscribe (1)
• Command (2)
• ReadWriteAllow (3)
• ReadOnlyAllow (4)
• Memop (5)
• Exit (6)
9

10. Command - 2
• Demande au pilot
d'effectuer une action
spécifique.
• Paramètres
– driver_number: u32
– command_number: u32
– data0: u32
– data1: u32
• L'action effectuée n'est
généralement pas
synchrone.
command (capsule_number,command_number, arg1, arg2)
not found
found
Get capsule with
id capsule_number
(SyscallDriverLookup trait)
CommandResult::failure
(ErrorCode::NODEVICE)
command (command_number, arg1, arg2, process_id)
CommandResult::failure... (ErrorCode::...)
no
is 0
yes
Is command_number a
valid action?
Application
CommandResult::failure
(ErrorCode::NOSUPPORT)
Execute or
schedule action
yes
no
Success?
CommandResult::success... (...)
User Space
Kernel
Syscall Capsule
Ok(())
Err(error)
Is the system call
allowed?
(SyscallFilter trait)
CommandResult::failure(errror)
10

11. Subscribe - 1
• Associe une fonction à
un rappel (événement)
d'un conducteur.
• Paramètres:
– driver_number: u32
– subscribe_number: u32
– callback: usize
– user_data: usize
subscribe (capsule_number,subscribe_number, upcall_ptr, user_data)
not found
found
Get capsule with
id capsule_number
(SyscallDriverLookup trait)
SyscallReturn::SubscribeFailure
(ErrorCode::NODEVICE, upcall_ptr, user_data)
no
yes
Is subscribe_number
less then
NUM_UPCALLS ?
Application
SyscallReturn::SubscribeFailure
(ErrorCode::NOSUPPORT, upcall_ptr,
user_data)
Register upcall
Ok (previous_upcall_ptr, previous_user_data)
User Space
Kernel
Ok(())
Err(error)
Is the system call
allowed?
(SyscallFilter trait)
SyscallReturn::SubscribeFailure
(errror, upcall_ptr, user_data)
allocate_grant (process_id)
Err(error)
Yes
Grant allocated?
SyscallReturn::SubscribeFailure
(error, upcall_ptr, user_data)
11

12. Grant
Allocated Grant Pointer
Allocated Grant
Unallocated Grant Pointer
Scheduled Task
Process Memory Space
Process Control Block
Grant 2
Grant 1
0x0040000
0x003FFC8
0x003FFC0
Task Queue
Kernel Memory Break
Driver Number 0x... Grant Pointer 1 (0x003FFC0)
Driver Number 0x... Grant Pointer 2 (0x003FFC8)
Driver Number 0x... Grant Pointer 3 (0x00000000)
Driver Number 0x... Grant Pointer n (0x00000000)
Driver Data Structure (T)
Padding
Upcall (0x003F050) User Data (32bits)
n
Upcall (0x00000000) User Data (32bits)
n-1
Upcall (0x003F200) User Data (32bits)
1
Upcall (0x003F000) User Data (32bits)
0
Upcall (0x00000000) User Data (32bits)
2
12

13. Yield - 0
• Fait passer le processus
en cours de l'état
Running à l'état Yielded.
– yield()
– yield_no_wait()
Process Control Block
Grant 2
Grant 1
0x0040000
0x003FFC8
0x003FFC0
Task Queue
Kernel Memory Break
Allocated Grant Pointer
Allocated Grant
Unallocated Grant Pointer
Scheduled Callback
Process Memory Space
Driver Number 0x... Grant Pointer 1 (0x003FFC0)
Driver Number 0x... Grant Pointer 2 (0x003FFC8)
Driver Number 0x... Grant Pointer 3 (0x00000000)
Driver Number 0x... Grant Pointer n (0x00000000)
13

14. AllowRead(Write/Only) – 3 et 4
• Partage des buffers
entre le noyau et
l'application.
• Paramètres:
– driver_number: u32
– allow_number: u32
– pointer: usize
– size: u32
allow_... (capsule_number, allow_number, buffer_ptr, len)
not found
found
Get capsule with
id capsule_number
(SyscallDriverLookup trait)
SyscallReturn::Allow...Failure
(ErrorCode::NODEVICE, buffer_ptr)
Application
Ok (previous_buffer)
User Space
Kernel
Syscall Capsule
Ok(())
Err(error)
Is the system call
allowed?
(SyscallFilter trait)
SyscallReturn::Allow...Failure
(errror, buffer_ptr)
yes
no
Is the provided buffer in the
application's memory?
SyscallReturn::Allow...Failure
(ErrorCode::INVAL, buffer_ptr)
no
yes
Is subscribe_number
less then
NUM_ALLOWS ?
Register buffer
Err(error)
Yes
Grant allocated?
SyscallReturn::Allow...Failure
(buffer, ErrorCode::INVAL)
SyscallReturn::Allow...Failure
(buffer, ErrorCode::NOSUPPORT)
allocate_grant (process_id)
14

15. Utilisation des appels de systèm
Allow RW or RO
(optional)
Subscribe
Command
Yield
Buffer
yes
Callback Ran?
no
Upcall
Run Upcall
Is Yielded?
Yes
Postpone
No
UnAllow RW or RO
(optional)
Buffer
not usable by
the application
15

16. États du processus
Get Next Process
Yes
Is Running? Is Yielded?
Has Scheduled
Upcalls?
Schedule
Is Faulted?
Restart Process Fault!
Systick
or
Kernel Task Done
No
No
Yes
Yes
No
Application
Kernel
Run Upcall
Set Running
16

17. API DU PILOTE SYSCALL
17

18. Trait SyscallDriver
pub trait SyscallDriver {
fn command(
&self,
command_num: usize,
r2: usize,
r3: usize,
process_id: ProcessId,
) -> CommandReturn {
CommandReturn::failure(ErrorCode::NOSUPPORT)
}
// suggested implementation
// self.apps.enter(processid, |_, _| {})
fn allocate_grant(
&self,
process_id: ProcessId
) -> Result<(), Error>;
}
18

19. Fonction de callback
typedef void (subscribe_upcall)(int, int, int, void*);
static void button_callback(
int btn_num,
int val,
int arg2,
void *ud
) {
// do work
}
19

20. Registration du pilot
• Chaque pilot a un numéro unique
• Pilot standard:
– 0x00000 ... 0x9ffff
• Pilot custom
– > 0xa0000
• En main.rs - trait SyscallDriverLookup
– fn with_driver (&self, driver_num: usize, f: F) -> R
20

21. Mot clés
• appel du systeme
• pilot
• capsule
• Running
• Yielded
• grant
• command
• subscribe
• upcall
• Callback
• yield
• allow
21

22. Questions
22