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Chapter 14: the Memory TCSS 422 A – Winter 2018 2/21/2018 Institute of Technology TCSS 422: OPERATING SYSTEMS OBJECTIVES Optional Ungraded Quiz – Synchronized Array Homework 2 Questions Memory API, Homework 3 Address Translation, Memory Segmentation, Ch. 14 Free Space Management . Memory API Ch. 15 . Address Translation Wes J. Lloyd Ch. 16 Institute of Technology . (Memory) Segmentation Ch. 17 University of Washington - Tacoma . Free Space Management TCSS422: Operating Systems [Winter 2018] TCSS422: Operating Systems [Winter 2018] February 21, 2018 February 21, 2018 L12.2 Institute of Technology, University of Washington - Tacoma Institute of Technology, University of Washington - Tacoma FEEDBACK FROM 2/14 FEEDBACK - 2 What is a bounded buffer, and when is it used? Homework #2: I’m using “for_each_process(task)” but Ubuntu can’t find this function… HELP!? What is piping in operating systems? In your kernel module make file, note the required files: All target: What is a condition variable? make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules Check to be sure you have this kernel sources: sudo apt-get install build-essential linux-headers-`uname –r` Helpful command - list kernel modules: $lsmod TCSS422: Operating Systems [Winter 2018] TCSS422: Operating Systems [Winter 2018] February 21, 2018 L12.3 February 21, 2018 L12.4 Institute of Technology, University of Washington - Tacoma Institute of Technology, University of Washington - Tacoma FEEDBACK - 3 “TCSS 422 has overlap with TCSS 333 for memory maps, memory/address translation”… Initial chapters of memory virtualization may be review However, memory virtualization spans chapters 13, 14, 15, CHAPTER 14: THE 16, 17, 18, 19, 20, 21, 22. (10 chapters) MEMORY API . Suspect this is not all review… TCSS422: Operating Systems [Winter 2018] TCSS422: Operating Systems [Winter 2018] February 21, 2018 L12.5 February 21, 2018 Institute of Technology, University of Washington - Tacoma Institute of Technology, University of Washington - Tacoma L12.6 Slides by Wes J. Lloyd L12.1 TCSS 422 A – Winter 2018 2/21/2018 Institute of Technology MALLOC SIZEOF() Not safe to assume data type sizes using Allocates memory on the heap different compilers, systems size_t unsigned integer (must be +) size size of memory allocation in bytes Dynamic array of 10 ints Returns Static array of 10 ints SUCCESS: A void * to a memory address FAIL: NULL sizeof() often used to ask the system how large a given datatype or struct is TCSS422: Operating Systems [Winter 2018] TCSS422: Operating Systems [Winter 2018] February 21, 2018 L12.7 February 21, 2018 L12.8 Institute of Technology, University of Washington - Tacoma Institute of Technology, University of Washington - Tacoma #include<stdio.h> FREE() What will this code do? int * set_magic_number_a() { int a =53247; return &a; } Free memory allocated with malloc() void set_magic_number_b() { Provide: (void *) ptr to malloc’d memory int b = 11111; } Returns: nothing int main() { int * x = NULL; x = set_magic_number_a(); printf("The magic number is=%d\n“,*x); set_magic_number_b(); printf(“The magic number is=%d\n“,*x); TCSS422: Operating Systems [Winter 2018] return 0; February 21, 2018 L12.9 Institute of Technology, University of Washington - Tacoma } 10 #include<stdio.h> What will this code do? DANGLING POINTER (1/2) int * set_magic_number_a() { int a =53247; Dangling pointers arise when a variable referred (a) goes return &a; Output: “out of scope”, and it’s memory is destroyed/overwritten } $ ./pointer_error The magic number is=53247 (by b) without modifying the value of the pointer (*x). void set_magic_number_b() The magic number is=11111 { int b = 11111; The pointer still points to the original memory location } of the deallocated memory (a), We have not changed *x but which has now been reclaimed for (b). int main() the value has changed!! { int * x = NULL; Why? x = set_magic_number_a(); printf("The magic number is=%d\n“,*x); set_magic_number_b(); printf("The magic number is=%d\n“,*x); return 0; TCSS422: Operating Systems [Winter 2018] February 21, 2018 L12.12 } 11 Institute of Technology, University of Washington - Tacoma Slides by Wes J. Lloyd L12.2 TCSS 422 A – Winter 2018 2/21/2018 Institute of Technology DANGLING POINTER (2/2) CALLOC() Fortunately in the case, a compiler warning is generated: Allocate “C”lear memory on the heap $ g++ -o pointer_error -std=c++0x pointer_error.cpp Calloc wipes memory in advance of use… size_t num : number of blocks to allocate pointer_error.cpp: In function ‘int* set_magic_number_a()’: size_t size : size of each block(in bytes) pointer_error.cpp:6:7: warning: address of local variable ‘a’ returned [enabled by default] Calloc() prevents… char *dest = malloc(20); This is a common mistake - - - printf("dest string=%s\n", dest); accidentally referring to addresses that have gone “out of scope” dest string=��F TCSS422: Operating Systems [Winter 2018] TCSS422: Operating Systems [Winter 2018] February 21, 2018 L12.13 February 21, 2018 L12.14 Institute of Technology, University of Washington - Tacoma Institute of Technology, University of Washington - Tacoma REALLOC() DOUBLE FREE Resize an existing memory allocation Can’t deallocate twice Returned pointer may be same address, or a new address Second call core dumps . New if memory allocation must move void *ptr: Pointer to memory block allocated with malloc, calloc, or realloc size_t size: New size for the memory block(in bytes) EXAMPLE: realloc.c EXAMPLE: nom.c TCSS422: Operating Systems [Winter 2018] TCSS422: Operating Systems [Winter 2018] February 21, 2018 L12.15 February 21, 2018 L12.16 Institute of Technology, University of Washington - Tacoma Institute of Technology, University of Washington - Tacoma SYSTEM CALLS brk(), sbrk() Used to change data segment size (the end of the heap) Don’t use these CHAPTER 15: ADDRESS Mmap(), munmap() TRANSLATION Can be used to create an extra independent “heap” of memory for a user program See man page TCSS422: Operating Systems [Winter 2018] TCSS422: Operating Systems [Winter 2018] February 21, 2018 L12.17 February 21, 2018 Institute of Technology, University of Washington - Tacoma Institute of Technology, University of Washington - Tacoma L12.18 Slides by Wes J. Lloyd L12.3 TCSS 422 A – Winter 2018 2/21/2018 Institute of Technology OBJECTIVES ADDRESS TRANSLATION Virtual mapping Address translation 64KB Address space Base and bounds example HW and OS Support Translation: mapping virtual to Memory segments physical Memory fragmentation Address Space TCSS422: Operating Systems [Winter 2018] TCSS422: Operating Systems [Winter 2018] February 21, 2018 L12.19 February 21, 2018 L12.20 Institute of Technology, University of Washington - Tacoma Institute of Technology, University of Washington - Tacoma BASE AND BOUNDS INSTRUCTION EXAMPLE Dynamic relocation Base = 32768 Two registers base & bounds: on the CPU Bounds =16384 OS places program in memory Fetch instruction at 128 (virt addr) ↑ Sets base register . Phy addr = virt addr + base reg . 32896 = 128 + 32768 (base) Execute instruction . Load from address (var x is @ 15kb=15360) Bounds register . 48128 = 15360 + 32768 (base) -- found x… . Stores size of program address space (16KB) Bounds register: terminate process if OS verifies that every address: . ACCESS VIOLATION: Virtual address > bounds reg 0≤ 푣푖푟푡푢푎푙 푎푑푑푟푒푠푠 < 푏표푢푛푑푠 Int x TCSS422: Operating Systems [Winter 2018] TCSS422: Operating Systems [Winter 2018] February 21, 2018 L12.21 February 21, 2018 L12.22 Institute of Technology, University of Washington - Tacoma Institute of Technology, University of Washington - Tacoma MEMORY MANAGEMENT UNIT DYNAMIC RELOCATION OF PROGRAMS MMU Hardware requirements: . Portion of the CPU dedicated to address translation Requirements HW support . Contains base & bounds registers Privileged mode CPU modes: kernel, user Base & Bounds Example: Base / bounds registers Registers to support address translation . Consider address translation Translate virtual addr; check if in Translation circuitry, check limits . 4 KB (4096 bytes) address space, loaded at 16 KB physical location bounds Privileged instruction(s) to Instructions for modifying base/bound Virtual Address Physical Address update base / bounds regs registers 0 16384 Privileged instruction(s) Set code pointers to OS code to handle faults 1024 17408 to register exception handlers 3000 19384 Ability to raise exceptions For out-of-bounds memory access, or attempts to access privileged instr. FAULT 4400 20784 (out of bounds) TCSS422: Operating Systems [Winter 2018] TCSS422: Operating Systems [Winter 2018] February 21, 2018 L12.23 February 21, 2018 L12.24 Institute of Technology, University of Washington - Tacoma Institute of Technology, University of Washington - Tacoma Slides by Wes J. Lloyd L12.4 TCSS 422 A – Winter 2018 2/21/2018 Institute of Technology OS SUPPORT FOR MEMORY OS: WHEN PROCESS STARTS RUNNING VIRTUALIZATION For base and bounds OS support required OS searches for free space for new process . Free list: data structure that tracks available memory slots . When process starts running . Allocate address space in physical memory . When a process is terminated . Reclaiming memory for use . When context switch occurs . Saving and storing the base-bounds pair . Exception handlers . Function pointers set at OS boot time TCSS422: Operating Systems [Winter 2018] TCSS422: Operating Systems [Winter 2018] February 21, 2018 L12.25 February 21, 2018 L12.26 Institute of Technology, University of Washington
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