FAME – Operating Systems - Etis

Transcription

FAME – Operating Systems
2012 – David Picard
contributors : Arnaud Revel, Mickaël Maillard
[email protected]
ÉCOLE NATIONALE SUPÉRIEURE DE L'ÉLECTRONIQUE ET DE SES APPLICATIONS
1. Introduction
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A very simple computer
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Goals of an operating system
–
–
Hardware management
Task management
●
OS families
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Features
–
–
●
Multitasking, multiuser
Architecture dependances
Unix and Linux history
CPU
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Microprocessor
CPU
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Microprocessor
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Memory
mem
CPU
Hard disk
keyboard
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Microprocessor
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Memory
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Many peripherals
Screen
mem
others
mem
CPU
peripherals
programs
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Memory :
–
Programs
mem
programs
●
CPU
peripherals
data
Memory :
–
–
Programs
Data
mem
programs
●
data
peripherals
data,
interactions
Memory :
–
–
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CPU
Programs
Data
Peripherals :
–
–
Data
Interactions (high priority data)
Programs
int main(int argc char ** argv)
{
int a, b, c ;
float *A, *B ;
/* check input */
if(argc < 3)
{
printf("usage : dotprod <a> <b>\n") ;
return 1 ;
}
/* read a from args */
a = atoi(argv[1]);
b = atoi(argv[2]) ;
...
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Instructions
●
Data
Programs
int main(int argc char ** argv)
{
int a, b, c ;
float *A, *B ;
/* check input */
if(argc < 3)
{
printf("usage : dotprod <a> <b>\n") ;
return 1 ;
}
/* read a from args */
a = atoi(argv[1]);
b = atoi(argv[2]) ;
...
●
instructions
●
data
Memory
data
instructions
Running a program
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CPU
EIP
…
0xAD00 :
0x1D04 :
0xAD08 :
0xAD0C :
...
Read instruction from
mem at adress
contained in EIP
register
instruction 1
instruction 2
instruction 3
instruction 4
mem
Running a program
●
CPU
EIP
…
0xAD00 :
0x1D04 :
0xAD08 :
0xAD0C :
...
●
mem at adress
contained in EIP
register
Execution
instruction 1
instruction 2
instruction 3
instruction 4
mem
Running a program
●
CPU
EIP++
…
0xAD00 :
0x1D04 :
0xAD08 :
0xAD0C :
...
instruction 1
instruction 2
instruction 3
instruction 4
mem at adress
contained in EIP
register
●
Execution
●
EIP Incrementation
mem
Running a program
●
CPU
EIP
…
0xAD00 :
0x1D04 :
0xAD08 :
0xAD0C :
...
instruction 1
instruction 2
instruction 3
instruction 4
mem at adress
contained in EIP
register
●
Execution
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EIP Incrementation
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Next cycle
mem
Interaction between programs,
memory and peripherals
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Memory:
–
–
–
–
–
Read data
Write data
Run instructions
depending on data in
memory
Run other program
contained in memory
...
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Peripherals:
–
–
–
–
Read data (e.g.
Keyboard)
Write data (e.g.
Screen)
Run instruction in case
of interaction (e.g.
power off buton)
...
Goals of an OS
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Manage programs
–
–
–
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Manage memory
–
–
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Start, stop, running, etc
Integrity, security
Communication between programs
Allocation
Permissions, security
Manage hardware
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Interface layer between programs and hardware
Handle hardware event (ex: interrupt signals)
Managing Hardware
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Accessing hardware
–
–
–
–
Programs may want to access to the leys pressed on a
keyboard, or write some characters on the screen, etc
The OS acts as an interface between programs and
peripherals
It translates the query of programs into commands to
peripherals
Simplicity gain for the programs, since the interface to
different peripherals is unique
Managing hardware
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Interrupts
–
–
Some peripherals may want to change the way programs
are running (think to the stop button of an assembly
chain)
The OS must handle signal coming from peripherals
Managing hardware
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Critical sections
–
–
The OS manages how requests to peripherals are
handled and scheduled
For instance, 2 programs printing a file should not end
with an entanglement of text coming out of the printer
Managing Tasks
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Context
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When a taks is running, the OS manages its context
(stack pointer, instruction pointer, loading libraries into
memory, etc)
Managing Tasks
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Context switch
–
–
Most OS can handle several programs running at the
same time. They manage the contexts of each program
and handle the switches from one task to another
Security is also a big deal when running several
programs (restrict permission of one task to read/write
memory zones of others for example)
Managing Tasks
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Communication between programs
–
–
Some programs must interact (exchange data, wait for
termination, etc)
OS handle how communication between programs is
done (called IPC – Inter Processus Communication)
OS Anatomy
libc
kernel
Operating System
applications
Task
management
toolkit
Memory
Management
Hardware
Management
hardware
OS families
●
By use :
–
–
–
Desktop: reactivity, many different programms, low
constraints
Real time: predictability, few known programs, strict
constraints
Embedded: very few known programs, very constrained
(limited mem, etc)
Kernel types
●
kernel :
●
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Monolithic : everything is in the kernel, device
drivers, mem management, network protocoles,
IPC, etc. (ex Linux, Solaris)
Microkernel : basic are done by the kernel (task
management, complex IPC). Other things are done
by programs (device drivers, memory management,
etc). (ex Mach, L4)
Comparison
Modular kernels
●
Monolithic, but
–
–
–
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Possibility to add/remove fonctionality while running
(device driver for ex)
Smaller (only necessary stuff is running)
Less safe (need to validate all drivers that will be loaded)
Ex : Linux
Common features
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Multitasking:
–
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Multi-user:
–
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Several programs can run at the same time
Several users can use the OS at the same time
Multi-architecture:
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Wide variety of architectures running the system
Multitasking
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Several tasks at the same time:
–
–
Handle creation and destruction
Handle access to resources
●
●
–
Scheduling
Critical resources
Integrity (permission, rights and so on)
Multi-user
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Several users on the system:
–
–
–
Handle critical resources
Integrity of users data
Handle communication between users
Multi-arch
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Different hardware configuration
–
–
Independence of programs to the architecture (e.g.
POSIX norm, ...)
Being able to run on several different arch (e.g. power,
x86, arm, sparc, ...)
History
●
●
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69 : Thomson et Ritchie
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First version of UNIX
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PDP7/9; kernel 16Ko; Process 8Ko, Files 64Ko
72 : Kernighan et Ritchie : C programing
language
73 : UNIX rewritten in C
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Process management
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File management
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Generic I/O
History
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75 : first porting of UNIX
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76 : 8/16 bits microprocessors
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77 : Thomson at Berkeley Univ
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500 installations
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79 : Porting to VAX and IBM
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82 : Sell by ATT
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Unix-based and Unix-like (100 000 install.)
History
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84 : Normalization
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DEC (Ultrix)
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Gould (UTX)
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HP (HP-UX)
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85 : MINIX by A. Tanenbaum
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88 : standard desktop system
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SUN/BULL/IBM…
History
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89 : first free BSD
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Sep 91 : Linux 0.01 (inspired by Minix)
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Oct 91 : Linux 0.03 (bash and gcc)
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Dec 91 : Linux 0.10 (first external contrib)
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Jan 92 : Linux 0.12 (virtual mem, GPL
licenced)
Mar 92 : linux 0.95 (init/login, X)
History
●
●
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93 : NetBSD and FreeBSD
Mar 94 : Linux 1.0 (production stable,
features comparable to UNIX)
Mar 95 : Linux 1.2 (several architectures,
modules)
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Jul 96 : Linux 2.0 (smp, Tux)
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Jan 99 : Linux 2.2
History
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99 : MacOSX (hybrid kernel)
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01 : Linux 2.4
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03 : Linux 2.6 (preemptible kernel)
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07 : Linux 2.6.23 (CFS scheduler)
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08 : Linux 2.6.26 (Kgdb)
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21 Jul 2011 : Linux 3.0.0 (13M lines of code)
Linux features
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●
Monolithic kernel
Modules : functionality can be added or removed (only SVR4.2 and
Solaris can do this)
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Kernel threads : some kernel features are independent
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Native multithreading
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Preemptible kernel: a process can be interrupted in kernel mode
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Multi-CPU support
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Many filesystems
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Many supported arch
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Small
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Performant
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Libre (free as in free speech)
Distributions
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Complete OS based on Linux kernel:
–
–
–
–
–
–
–
Linux kernel
C library and compiler (mostly gcc)
Bootloader (grub, lilo, ...)
Init system to start the system (networking, printing, user
interfaces, …)
Shell (bash, dash, ksh, …)
Package manager (apt, rpm, portage, …)
Package repository loaded with verified programs
Distribution families
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Deb: Debian, ubuntu, and derived
–
–
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RPM: RedHat, SuSE, Mandriva, and derived
–
–
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*.rpm packages
RedHat : server, Mandriva : desktop
Slackware
–
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*.deb packages
Debian : server, Ubuntu : desktop
The Great Old One (paquets *.tgz)
Sources based: gentoo, sourcemage, ...
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–
Compile all software from sources
Gentoo : portage package manager probably the best ever
Fundamental concepts
●
Execution modes (hardware feature)
–
User mode: instructions of the running program
●
●
●
–
Reserved memory zone
Specific context (stack pointeur, eip, ...)
Restricted permissions
Kernel mode (supervisor): instruction of the kernel
●
●
●
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All memory zones
Specific context
All permission
Accessed by interrupt (either software or hardware)
Fundamental features
●
●
●
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Process: instance of a running program and its
associated context
Files: everything is files, devices, documents,
etc
Permissions: files have different permission
levels (user, group, other)
Reentrant: several processes can be in kernel
mode at the same time (check your local
variable!)
User/Kernel Mode
●
Using the computer is divided into 2 execution
modes:
–
–
●
User mode is for user programs
–
–
–
●
kernel mode
user mode
root
Services (printing, web server, ...)
Real users (mail, office, games, devel, …)
Kernel mode is for... kernel programs
Modes and permissions
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Memory is restricted to modes
–
User mode applications cannot access to
●
●
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Kernel memory zones
Memory zones of other applications
Most peripherals
To handle permission, most processors have
execution modes
–
–
A restricted mode corresponding to user mode
An administrator mode corresponding to kernel mode (or
supervisor, ...)
Acess to kernel mode
●
Memory zones of the kernel are accessible only
in supervisor
–
–
–
–
–
Not accessible in user mode
Access by an interrupt
System switch to supervisor mode
Kernel handles interrupt
Back to user mode and continue user application
Switch to kernel mode
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Accessing kernel mode is done
–
By hardware interrupts
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When errors occurs
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Switch to supervisor mode and execution of interrupt procedures
System raises an exception, switch to supervisor mode and
execution of exception procedures
When programs ask services to the kernel by a System
Call
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Software interrupt raised by an application
Switch to supervisor mode and execution of procedures attached
to the system call
Interruptions
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Signal raised by
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A peripheral
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Processor instruction (soft interrupt)
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Occurs at any time
Procedure handling these are called drivers
Special instruction allowing to switch to supervisor
Procedures related to interruptions are
initialized at system boot
Part of kernel code
Exceptions
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Processor responses to incorrect instructions
–
–
–
Interrupt raised by the processor
Signals errors in the running procedure (permission fault
for example)
Allow the kernel to handle errors
●
For example, allocate demanded resources (program asking for
a non-allocated memory zone, ...)
Interrupt handling
●
When an interrupt occurs, the processor
execute a procedure initialized at boot time
User mode
Program 1
System
call
Kernel mode
Kernel proc
Program 1
Interrupt
return
Clock
interrupt
Kernel proc
Program 2
Interrupt
return
System calls
●
Are function that:
–
–
–
●
Are called in user mode
Are executed in supervisor
Return in user mode (in the calling program)
The system call is asked by a unique software
interruption (0x80)
–
–
–
–
Does the switch to supervisor
System calls are identified by numbers
The number of the system call is loaded in a register
A table allows to know which procedure to call depending
on the number present in the register
Linux 0.01
●
System calls are available in glibc
#define _syscall0(type,name) \
type name(void) \
{ \
type __res; \
__asm__ volatile ("int $0x80" \
: "=a" (__res) \
: "0" (__NR_##name)); \
if (__res >= 0) \
return __res; \
errno = __res; \
return 1; \
}
Kernel control path
●
●
kernel control path is the sequence of
instruction executed by the interrupt procedure
Several kernel control path can be entangled
–
–
●
Ex: a process asks for a non available resource, another
process is executed and asks for a resource also
An interrupt is raised during a kcp
Need for a reentrant kernel

FAME – Operating Systems - Etis

Transcription

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