ComputerFundamentals Logical AddressSpace (2/2)
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Computer Fundamentals Logical Address Space (2/2) Grau en Intel·ligència Artificial Xavier Martorell Xavi Verdú Facultat d’Informàtica de Barcelona (FIB) Universitat Politècnica de Catalunya (UPC) 2021-2022 Q1
Transcript of ComputerFundamentals Logical AddressSpace (2/2)
Computer FundamentalsLogical Address Space (2/2)
Grau en Intel·ligència Artificial
Xavier MartorellXavi Verdú
Facultat d’Informàtica de Barcelona (FIB)Universitat Politècnica de Catalunya (UPC)
2021-2022 Q1
Creative Commons License
This work is under a Creative Commons Attribution 4.0 Unported License
The details of this license are publicly available athttps://creativecommons.org/licenses/by-nc-nd/4.0
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Table of Contents
• This lesson consists of three main parts1) Basic Concepts2) Libraries and OS suport
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Libraries
• Library: a file that encapsulates a set of object files• Libraries grant independency
• A high-level code is independent of OS and Hw architecture, but …• … executables are created for a particular OS and Hw architecture
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(sprintf.o)
(strlen.o)
(write.o)
Library…<sprintf>: {
…}…
…<write>: {
…}…
ObjectCode
(hello.o)
…call sprintf…call write…
Types of Libraries
• Language Libraries• Bind a language to a particular OS, but independently of the hardware architecture• Provide functions of the programming language• Sometimes they are self-contained (e.g. math): independent of OS• Sometimes they request services to the OS (e.g. sprintf, cin, cout…)
• System Libraries• Bind an OS to a particular Hw architecture (independent of the high-level code)• Include functions that invoke services/routines of the OS (e.g. write, open, …)• Depends on the type of Operating System and the architecture of the CPU
• Examples of incompatibility: • Linux 32 vs 64 bits, CPU Intel vs ARM, Ubuntu vs OpenSUSE, …
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Global Picture
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ObjectCode
(hello.o)
…call sprintf…call write…
…<sprintf>: {
…}…
…<write>: {
…}…
Ope
ratin
gSy
stem
Hard
war
e
LanguageLibrary
SystemLibrary
ObjectCode
(obj2.o)……call write…
Binary (executable) file
Let’s assume an example
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#include <unistd.h>#include <stdio.h>
int global = 4;
int main(int argc, char **argv){char buf[512];int num;
num = sprintf(buf, "Hello World %d!\n", global);write(1, buf, num);
return 0;}
High Level Language Codespecified in a file thatcannot be understood bythe CPU to be executedright awayHigh-Level
Code(hello.c)
• From high-level code to program execution
Let’s assume an example
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#include <unistd.h>#include <stdio.h>
int global = 4;
int main(int argc, char **argv){char buf[512];int num;
num = sprintf(buf, "Hello World %d!\n", global);write(1, buf, num);
return 0;}
Including Header Files
Global Variable
Local Variables
Calling to external functions
Header files contain requiredinformation for the compiler aboutexternal components used in thiscode, such as “sprintf” and “write” functions
Return the exit status of the program,Indicating success(0) or some failure(1)
Static versus Dinamically linking
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• Static linking• The codes of libraries are included INSIDE the executable• Waste of space (in disk when stored, and in memory when running)
• Different programs may use the same libraries• Static libraries: “.a” in UNIX-like OS; “.lib” in Windows-like OS
• Dynamic linking• The linking stage is delayed to run-time. Thus, the code is not included in the
program• Sharing libraries• Save space in both disk and memory
• Different programs can access to a shared library loaded in memory• Dynamic libraries: “.so” in UNIX-like OS; “.dll” in Windows-like OS
Static linking
• Static compilation and linking phases
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sda1
sda2
sda3
sda4
hello
L1sL2s
Static librariesArchives(lib*.a)
StaticExecutableBinary file
#include <unistd.h>#include <stdio.h>
int global = 4;
int main(int argc, char **argv){char buf[512];int num;
num = sprintf(buf, "Hello World %d!", global);write(1, buf, num);
return 0;}
Files in the disk
Process with static libraries
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Core
Core
Core
C
L2
L2
L2
L2
L3 RAM Node 0
Operating System LinuxWindows...
code data BSS
stack
Threadsstacks
I/O to devices, disks...
Virtual memory space (process)
Virtual memory space (OS)
Physical memory
code
data
Threadsstacks
Memory mapping(to OS and process)
hello
Logical addressesrefer to virtual memory addressesdue to the OS support
Files in the disk
Dinamically linking
• Dynamic compilation and linking phases
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#include <unistd.h>#include <stdio.h>
int global = 0;
int main(int argc, char **argv){char buf[512];int num;
num = sprintf(buf, "Hello World %d!", global);write(1, buf, num);
return 0;}
sda1
sda2
sda3
sda4
hello
L1L2
(Shared)ExecutableBinary file
Shared libraries(lib*.so)
Files in the disk
Process with shared libraries (Dynamic linking)
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Core
Core
Core
C
L2
L2
L2
L2
L3 RAM Node 0
Operating System LinuxWindows...
code
data
BSS
stack
sharedlibrary
L2
Threadsstacks
I/O to devices, disks...
Virtual memory space (process)
Virtual memory space (OS)
Physical memory
code
data
Threadsstacks
Memory mapping(to OS and process)
hello
L1L2
sharedlibrary
L1
Files in the disk
OS Support
• Memory regions are private per process• In multiprogrammed systems (multiple processes
are alive at a time) the OS must protect mem regions• Contents usually are distributed in remote
physical memory locations
• The OS memory zone holds the kernel andall required internal data and routines
• The OS memory space NEEDS protection
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Core
Core
Core
Core
L2L2L2L2
L3 RAM Node 1
Core
Core
Core
Core
L2L2L2L2
L3 RAM Node 0
Process 1
Process 3
Process 2
Process 5
Process 4
OS
Processes contents
0x00000000
0xFFFFFFFFPhysical memory
Process Contents in Memory
• Stack: dynamic mem• Function arguments• Local Variables
• Shared libraries: Code, data…
• Heap: dynamic mem• Mem allocated at runtime
• Data: .bss & .data• Global variables
• Code: .text• Instructions
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Core
Core
Core
Core
L2L2L2L2
L3 RAM Node 1
Core
Core
Core
Core
L2L2L2L2
L3 RAM Node 0
P1
P3
P2
P5
P4
OS
0x00000000
0xFFFFFFFF
Stack
Heap
Data
Code
0xFFFFFFFF
Shared libraries
0x00000000
Physical memory Virtual memory
Syscalls related to Memory Management
• The Heap is mainly employed for dynamic data structures• E.g. Structures used only for a period of time, unknown memory size requirements,
allocated and deallocated often
• Syscalls related to heap management• Memory allocation
• malloc (C library)• new (C++ library)
• Memory deallocation• free (C library)• delete (C++ library)
• All above calls invoke a system call to modify the limit of the Heap Mem Zone (brk)
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Memory Allocation
• (type) malloc(int size); // C language• Returns the starting @ of the newly allocated size Bytes in the HEAP
• new type[size]; // C++ language• Returns the starting @ of the sizeof(type)*size Bytes in the HEAP
• Behavior• Before allocating @, it checks whether the HEAP has space enough to hold size bytes
• If not, the OS increases the limit of the HEAP (sbrk)• The HEAP size is increased by a configurable number of bytes to reduce the number of times it
has to be increased• The object memory zone is allocated in the HEAP following a placement algorithm
• Can group objects by their size… 17
Memory Allocation
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Stack
Heap
Data
Code
Stack
Data
Code
Starting statusAfter calling:int *ptr = (int) malloc(4*sizeof(int));
Stack
Heap
Data
Code
After calling:char *string = (char) malloc(2*sizeof(char));
2 chars2 Bytes
Memory Deallocation
• free(pointer); // C language• delete [] pointer; // C++ language
• In both cases the memory zone pointed by the pointer is released
• Behavior• Deallocation of the memory zone pointed by the input parameter• The OS will consider to reduce or not the HEAP memory space• A pair of lists are maintained by malloc/new/free/delete
• List of objects allocated• List of objects deallocated (may be merged)
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Memory Deallocation
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Stack
Heap
Data
Code
Stack
Data
Code
Starting statusAfter calling:free(string);
Stack
Heap
Data
Code
After calling:free(ptr);
Final relation with physical memory
• Virtual memory• Split in pages (4KB usually, can be 2-4 MBytes)• A page can be
• Valid and present (in memory)• Valid and not present (in memory)• Invalid
• Physical memory• Split in page frames
• Same capacity as virtual pages• OS keeps information about
• Available frames• Busy frames 21
code data
Virtual memory space (virtual pages – 4 KB)
Physical memory space (page frames)
Core
Core
Core
Core
L2L2L2L
L3 RAM Node 0
When Memory is exhausted…
• OS constantly checks memory availability (used vs free) of the system
• If the memory becomes exhausted (less than a given availability threshold) OS starts an alternative suport approach:
• Difference between page replacement (paging) and process replacement(swapping)
• Pages are selected->Written to the swap area [if modified]->Reallocate othervirtual pages
• Swap area: special memory area, usually in a storage device (e.g. disk) totemporary hold contents of the main memory that have not space enough
• It is considered as additional space to the physical memory22
Bibliography
• Computer Systems – A Programmer’s perspective (3rd Edition)• Randal E. Bryant, David R. O’Hallaron, Person Education Limited, 2016
• https://discovery.upc.edu/permalink/34CSUC_UPC/11q3oqt/alma991004062589706711• Chapter 9
• Computer Organization and Design (5th Edition)• D. Patterson, J. Hennessy, and P. Alexander • http://cataleg.upc.edu/record=b1431482~S1*cat
• Several Chapters
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