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Embedded Linux Kernel Internals using ARM and Device Drivers

"Embedded Linux Kernel Internals using ARM and Device Drivers" (ELKIADD) is an Ineffable, Comprehensive, Hands-on, project based career oriented, training program for BE, B Tech, ME, M Tech from the streams of Electronics, Computer Science, Information Technologies, Instrumentation or Master of Computer Applications.

This trainig aims at building your career with respect to innovative technologies related to Embedded Linux, ARM, Device Drivers, System Software, System Engineering.

The concepts absorbed during this training should help you in any domain where electro-mechanical, electronic devices are designed. You will be efficient with respect to incorporating intelligencs in the devices.

#Device Driver carrierforengineers

Embedded Linux Kernel Internals using ARM and Device Drivers

Data Structures with C using Linux, vim, gcc, gdb, SCCT http://www.emblogic.com/358/data-structures-c-programming

Introduction to Structure

Structure is a user-defined datatype in C language which allows us to combine data of different types together. Structure helps to Construct a complex data type which is more meaningful. It is somewhat similar to an Array, but an array holds data of similar type only. But structure on the other hand, can store data of any type, which is practical more useful.

For example:- If I have to write a program to store Student information, which will have Student’s name, age, branch, permanent address, father’s name etc, which included string values, integer values etc, how can I use arrays for this problem, I will require something which can holds data of different types together. In structure, data is stored in form of records.

Struct syntax:-

struct name { structure -element 1; structure -element 2; – }; As you can see in the syntax above, we start with the struct keyword, and name is user defined data type, then inside the curly braces, we have to mention all the member variables, which are nothing but normal c language variables of different types like int, float,array etc. After the closing curly braces, we can specify one or more structure variables, again this is optional. Note:- The closing curly braces in the structure type declaration must be followed by a semicolon(;).

Example of Structure:-

struct student { char name[25]; int age; char branch[10]; char gender; }; Here struct student declares a structure to holds the details of a student which consists of 4 data fields, namely name, age, branch and gender. These fields are called structure elements or members. Each member can have different datatype, like in the case, name is an array of char type and age is of int type etc. student is the name of the structure and is called as the structure user defined data type.

Shell Scripting using Bash

Embedded Linux on ARM.Porting Embedded Linux on ARM Systems using Storage

Linux Boot-Up Process

STAGE1: BIOS This is the first step of booting process. When you power on your machine the stable power is supplied to all the devices connected to that machine such as Motherboard HDD's, Mouse, keyboard etc. The most important device is Processor(CPU), when supplied with power will start running it’s sequence of operations stored in it’s memory. The first instruction is run to pass control to BIOS(Basic Input/Output System) to do POST(Power On Self Test). Once the control goes to BIOS it will take care of two things, Run POST operation and Selecting first Boot device. POST operation: POST is a processes of checking hardware availability. Selecting First Boot Device: Once the POST is completed BIOS will have the list of devices available. BIOS memory will have the next steps details like what is the first boot device it has to select etc. STAGE 2: BOOT LOADER STAGE 1 (MBR) Once the BIOS gives control back to CPU, it will try to load MBR of the first boot device( generally HDD). MBR is a small part of Hard Disk with just a size of 512 Bytes. MBR resides in first sector of HDD. MBR(Master Boot recorder) is a location on disk which have details about primary boot loader code( of 446 Bytes) ,partition table information(64 Bytes ), validation check (2 Bytes) Primary Boot loader code: This code provides boot loader information and location details of actual boot loader code on the hard disk. This is helpful for CPU to load second stage of Boot loader. Partition table: MBR contains 64 bytes of data which stores Partition table information . Validation check : If MBR gets corrupted this is used to retrieve it. Once your CPU knows all these details, it will try to analyse them and read the first portion of MBR to load Second stage of Boot loader

STAGE 3: BOOT LOADER STAGE 2 (GRUB LOADER) Stage 1 boot loader start second stage by loading Boot loader into memory. In this stage GRUB(Grand Unified Boot loader) which is located in the first 30 kilobytes of hard disk immediately following the MBR is loaded into RAM for reading it’s configuration and displays the GRUB boot menu to the user. GRUB loads the user-selected (or default) kernel into memory and passes control on to the kernel. If user do not select the OS, after a defined time-out GRUB will load the default kernel in the memory for starting it. STAGE 4: KERNEL Once the control is given to kernel which is the central part of all your OS and act as a mediator of hardware and software components. Kernel once loaded into to RAM it always resides on RAM until the machine is shut-down. Once the Kernel starts it’s operations the first thing it do is executing INIT process. STAGE 5: INIT init(initialization) process is the root/parent process of all the process which run under Linux/Unix. The first process it runs is a script at /etc/rc.d/rc.sysinit which check all the system properties, hardware, display, SElinux, load kernel modules, file system check, file system mounting etc.

STAGE 6: RUNLEVEL Based on the appropriate run-level, scripts are executed to start/stop various processes to run the system and make it functional. INIT process read /etc/inittab which is an initialization table which defines starting of system programs. INIT will start each run level one after the other and start executing scripts corresponds to that runlevel Once the initialization process completes mandatory run level and reach to default runlevel set in /etc/inittab, init process run one more file /etc/rc.local which are the last commands run in initialization process or even booting process. Once everything is completed the control is given back to the kernel. And now you may login ……….. ENTER PASSWORD:

LINKED LIST

What is Linked list ? Just as the name suggests LINKED LIST it is a list of data that is connected in a such a way that the address of next element or data is stored in the previous data . To access the linked list all we need to do is access the address of first element and that will automatically print the whole list ( because every element is connected with each other).

Why do we use it ? As we know in ARRAY we can store data of similar data type. So array has this con that it can only store data of similar data type. So to overcome this we introduced Linked List . A linked List can store data of multiple data types . This is the main advantage of using a Linked List . Another advantage of using Linked List is the operation of insertion and deletion become easy. Because a LINKED LIST IS MADE UP OF VARIOUS *NODES ( A Node is nothing but it is a structure that holds a data of any data type and Address of type structure). How to use it ? Declaration: struct Linked_List { int Data; struct Linked_List *Node; } This structure has data of data type int and its second variable of struct type Linked_List *Node is used to hold the address of next variable . For making a linked list we need to malloc (to allocate the memory for every node) every single node. As many elements as we want to enter.

-----IMP---- The head node of a linked list should be fixed so that we can access whole Linked list. If we will delete the Head node of the linked list the whole linked list will get destroyed and will get lost in the memory space (as observed) . To End a Linked list we must need to store the Null instead of address so that it won’t access any other . Figure

Head Node

End Node

Operations we can perform

We can perform various operations like insertion , deletion and sorting etc. To perform any operation first we have to know about the position the pointer where it actually is present , which element or node is it representing at present . While making a head node we introduce a variable of type structure that is defined above named temp . All the operations that we want to perform on linked list is performed by the help of temp variable . We never move head node anywhere (Head node is fixed ) . According to our operation we write algo and make functions .

Techniques Using Linked List Stacks – Works on LIFO Technique (Last In First Out) Queues – Works on FIFO Technique (First In First Out)

Types of Linked List Singly Linked List – In this each node has data and pointer pointing towards next Node . As mentioned above in Figure . Doubly Linked List - In this we add a pointer to the previous node . Thus we can go in both forward and backward direction

Circular Linked List – In this the end node of Linked list holds the address of the head node . So it makes up a circle .

#linux #emblogic

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MUTLITHREADING IN C

Thread:A thread is a single sequence stream withing a process as threads have some of the propeerties of the processes, also sometimes referred as lightweight processes.

How a process differs from threads:

Threads as not independent of one other like processes are as a result threads shares with other threads their code section , data section and many OS resuources like open files and signals .Though like process , a thread has its own program counter (PC) , a register set and the stack space.

Use of Multithreading:

threads are popular way to improve application through parallelism like in a browser , multiple tabs can perform different searches .

Thread operates faster than a process due to following reasons:

· threads creation is much faster.

· context switching between threads is much faster

Functions to create a multithreaded programs:

pthread_create:

· function to create a thread , takes 4 arguments ie. first argument is thread_id which is set be this function

· second argument specifies attributes, if value is NULL so default attributes are used.

· third argument used to pass the name of function to be executed by the thread to be created

· forth argument is used to pass the arguments to be passed to the thread function

pthread_join :

equivalant of the wait() call for the processes , pthread_join blockes the calling thread until the thread with identifier equal to the first argument terminates

pthread_exit:

used to exit from the thread function in pace of pthread_exit we can even use return to exit from the thread function.

Compiling the multithreaded program:

to compile a multithreaded program in gcc we need to link it with the thread pthread library ie -lpthread.

DYNAMIC MEMORY ALLOCATION

In industry memory management is very important. There are two types of memory which is used by the program, one is Stack segment and another is Heap segment. Stack is a special area of Computer’s memory which stores the temporary variables created by the functions. In stack variables are stored in runtime. It is a temporary storage memory. Heap is a memory used to store global variables. Heap is not managed by the CPU unit. It supports dynamic memory allocation. Dynamic memory allocation is done with malloc(), calloc() and realloc() function. Malloc: malloc is used to allocate a block of memory in the heap segment. Malloc allocates the memory at run time. Malloc allocates the memory in the heap segment. Dynamic memory is not cared by the CPU, so it’s required to free the memory after the use to prevent the memory leakage. Syntax: ptr=(int*/char*)malloc(byte-size); where ptr is a pointer type of variable which points the base address of the allocated memory in heap segment. After that is pointer typecast of the data. If we allocates the ‘0’ bytes to the malloc then also it reserve some memory which is of size 32Kbytes. The usable size of the malloc is checked by the malloc_usable_size which is 24Kbytes, and it keeps extra 8bytes with it which is chunk size. Working of malloc function: When we gives the size to allocate then it checks the threshold of malloc and then checks it in memory pages if available then then it allocates the memory blocks otherwise memory mapping comes into the picture(mmap). Malloc allocates the memory in heap segment which have fixed size of 130Kbytes. When we allocates the memory then it points the address of the page which is of 130Kbyte’s size if the requirement is more than heap then the size of heap then it calls the extra memory by mmap. On the successful of malloc it returns the address of the allocated space. On the failure of malloc it returns the NULL . Calloc: calloc is used to allocate dynamic memory. Dynamic memory is allocated on run time . Calloc is similar to malloc the difference is, that the default values of the allocated blocks are zero in calloc and in malloc the default values are garbage. Realloc: realloc is used to allocate the memory on run time whenever the extra memory required on the run time. Syntax: ptr_new=(typr-caste)realloc(ptr,new_size in bytes); where ptr_new is the address of the new allocate space, ptr is the previous size of allocated memory. Working of realloc function: when realloc function is used then first it checks the available space in that page if the required space is available then it added the requested blocks of memory. If the size is not available then an extra page comes through the memory mapping concept and reallocates the space requested and it copies the data of the current address to new allocated space and frees the previous memory. Malloc is slightly faster than calloc than realooc.

MEMORY LEAKAGE

Memory leak occurs when we create a memory in heap and forget to delete it .Memory leaks are particularly serious issues for programs like deamons and servers which by definition never terminate.

Memory leak should always be checked and the memory is always a constraint on a device. If there are many memory leakage in the device memory , the device will run out of memory faster, though there is unused memory there.

How to avoid memory leakage: To avoid memory leaks,memory allocated on heap should always be freed when no longer needed.

Methods to check memory leakage:

1. GDB: Typical usage of GDB runs as follows: After starting GDB, we set breakpoints,which are place where the execution of code wish to pause.Each time GDB encounters a breakpoint, it suspends its execution of the program at that point, giving us a chance to check the values of various variables. INVOKING GDB: Before starting make sure you complied the programs with -g option, without -g GDB would be useless since no information of the variable and function names , line numbers and so on. Syntax: gcc -g program.c TO start GDB: syntax: gdb a.out (in place of a.out any executable file can be there). ` RUN GDB: syntax: r or run

BREAKPOINT SET: b main (or function name) / b 10 (10 here is line number) DISPLAY AND PRINT COMMAND: disp variable will display the value of variable at every time the program pause. Print : p variable will print the current value of the variable NEXT (n ) or STEP (s) command: s will pause the program execution at the start of the function syntax: s n will move to the next line of execution. Syntax: n QUIT COMMAND: q will quit the program in execution. Syntax: q 2. Valgrind: Valgrind is primarily a memory checker tool(Memcheck). Cachegrind :CPU cache profiler. Callgrind:provides more callgraph info DRD:pthread bug detector. HELGRIND:Data race detector for multithreaded applications. Massif:Heap profiler MEMCHECK:memory bugs detector, includes out-of- bounds(OOB),accesses(READ/WRITE UNDER/OVERFLOW),unitialized data accesses,UAF,UAR,memory leakage, double free and overlapping memory region bugs. This is the default tool 3. ASAN: Purpose: assign ASAN with complier GCC. Usage: -fsanitize=address (address flag must be used). 4:KASAN(KERNEL SPACE SANITIZE): Purpose: debugging kernel space. Usage: -fsanitize=kernel_address 5:MSAN(MEMORY SANITIZIER): Purpose: UMR detector Usage: -fsanitize=memoryFPIE

6:TSAN(THREAD SANITIZIER) Purpose: data race detector Usage: -fsanitize=thread 7:LSAN(LEAK SANITIZER): Purpose: Memory Leakage detector Usage: fsanitize= leak 8:UBSAN(UNDEFINED BEHAVIOR SANITIZER): Purpose:Undefined behavior sanitize Usage: -fsanitize=unidentified

#linux #memory leakage

Introduction to C

C is a general purpose high level programming language used to develop portable applications and firmware. It is originally designed to develop system software and operating systems. C was invented by Dennis's Ritchie at bell labs in the 1972s. C has a primary application of Unix operating system. C have a main features low-level access to memory, simple set of keywords and clean style. Because of these features, this language is a suitable language for operating system development. After C, I follow the syntax of many developed language PHP, Java, Java script etc. C was initially used for system development work, particularly program of the system operating system. C was adopted a system language because it produce code that runs nearly as fast as the written code of assembly language. Developing programs using c requires software called integrated development environment (IDE) such as turbo c, codeblocks, visiual studio etc. the integrated development environment mainly three programs: 1. Text editor 2. Compiler 3.Debugger. 1 . Text editor :- it is used to type of instructions of program which is called of source code. Source code is stored in c file. 2. compiler:- it is used to translate instructions of program into machine language which is called binary code. 3. Debugger:- it is used to find bugs(errors) within programs.

Keyword:- keywords are p redefined word for performing various type of c. there are total 32 keywords available in c. example :- char,float,int etc.

Variable:- variable are new words created by us for storing data. Its value changes during execution programs. Example :-a,b,c, num, sum etc.

Constant:- Constant refer to the fixed value of that does not change during execution of program. No matter where we use it in program, it meaning always remains same. Example :-5, 34.33, -71 etc.

Operator :- symbols that are used to perform operations between variable are called operators. Example:- +,-,*, / = etc.

Application and Uses Language:-

C is mainly used to develop system software such as operating system, compiler etc. But it can also be used for developing and kind of application software such as commercial, scientific, games etc.

Advantage of C Language:-

1. C language is a building block for many other currently known language. C language has variety of data types and powerful operator. Due to this, program written in c language are efficient,fast and easy to understand. 2. C is highly portable language. This means that c programs written for one computer can easily run on another computer without any change or by doing a little change. 3. There are only 32 keywords in ANSI c and its strength in built in functions,several standard functions are available which can be used for developing program.

Disadvantage of C:-

1. C does not have concept of oops, that’s why c++ is developed. 2. there is no run time checking in c language. 3. there is no strict type checking. 4. C does not have the concept of name space. 5. C does not have the concept of constructor or destructor.

Gcc Compiler

Any c file, a user wants to compile is not directly compiled. For example, there is c file having a name hello.c, this hello.c file is not directly provided to the compiler. Hello.c file first of all provided to the gcc preprocessor , this preprocessor converts this hello.c file into hello.i file. This hello.i file consists of two file stdio.h and hello.c file. The combination these two files together makes a new file which is hello.c file . This hello.c file is provided to the gcc compiler. The gcc compiler is basically a two pass compiler which passes file two times . Then the file moves to the lexical analysis ,this lexical analysis breaks the content of file into tokens , then the tokens are provided to the syntax analysis which analysis all the tokens of file according to the c format ,this analysis gave us an errors ,saying that tokens used are appropriate or not .After the analysis process, file passes through the intermediate code generation, code optimization and object code generation. After the 2-pass compilation process, the format of file changes into different format which is in hello.s format .The output of the compiler is provided to the assembly, which is in the format of hello.s file. This hello.s file through assembly passes to the assembler. Assembler converts this hello.s file into hello.o file. This hello.o file passes through the symbol table, data segment and code segment process . After passing through these processes, file is provided to linker .The output of linker generates a new file named as a.out file which is in executable format. This executable file is then provided to the executable linkable format (elf), data segment and code segment.

After this whole process loader loads the file into the RAM. File spreads out in the ram. Ram is basically a process context (virtual address space content ) which consists of stack segment, file descripter, data segment and code segment. Stack segment consists of local variable of the file. File descripter consists of three ports 0,1,2 . These three ports are connected to the standard input, standard output and standard error respectively via stream. Stream is used for moving data wheather for input, output or for error. Standard input is used for entering the data to the port 0. standard output takes out the data from port 1. And standard error is to takes out the error from port 2. Data segment consists of various variables like global variable, static variable, extreme variable, register variable, volatile variable, constant variable, macros variable and preprocessor directive. Code segment consists of compiled code. Stack segment, file directive, data segment and code segment all these have some logical addresses.

Installation to Fedora 29

Following are the minimum requirements for Fedora 29 workstation :-

2 GHz Dual Core processor 2 GB RAM. 15 GB unallocated Hard Disk. Bootable Media (USB / DVD).

Installation steps :-

(Step1) :- Download thee fedora 29 workstation ISO file :--

Once the ISO file is downloaded ,then burn it either in USB or DVD and make it bootable.

(Step2) :- Boot your system with bootable media (USB or DVD) :--

Reboot your system.Set the boot medium as USB or DVD from Bios settings so system boots up with bootable media.

(Step3) :- Choose Start Fedora-Workstation-Live- 29 :--

When the system boots up with bootable media then to begin with installation on your system’s hard disk, choose “Start Fedora-Workstation-29 Live“

(Step4) :- Select Install to hard drive option :--

Select “Install to Hard Drive” option to install Fedora 29 on your system’s hard disk, you can also try Fedora on your system without installing it, for that select “Try Fedora” Option.

(Step5) :- Choose appropriate language for your Fedora 29 Installation :--

In this step choose your language which will be used during Fedora 29 Installation.

(Step6) :- Choose Installation destination and partition scheme :-- In this step we will choose our installation destination, means on which hard disk we will do installation. In the next screen we will see the local available hard disk, select the disk that suits your installation and then choose how you want to create partitions. If you choose “Automatic” partition scheme, then installer will create the necessary partition for your system automatically but if you want to create your own customize partition scheme then choose “Custom” option.

CLICK ON DONE !

Now I show u that how to create LVM(Local Volume Manager) based custom partitions :-- In my case, I have around 1.80 TiB unallocated hard drive, so I will be creating following partitions on it :-

/home >>> 450 GiB /(root) >>> 240 GiB boot/efi >>> 2 GiB /boot >>> 2 GiB /var >>> 50 GiB swap >>> 24 GiB

CLICK ON DONE ! AND CHOOSE “ACCEPT CHANGES”.

(Step7) :- Select the time zone and begin installation :-- Here you can select the time zone which suits to your system and click on “Begin Installation”. In this step we can see Fedora 29 Installation has been started and it is in progress. Once the Installation is completed, you will be prompted to restart your system. Click on Quit and reboot your system. Don’t forget the Change boot medium from Bios settings so your system boots up with hard disk.

(Step8) :- Set User name and Password and Start using Fedora 29. :-- Now specify the local account (user name) and its password, later this account will be used to login to the system. Click on Next And finally, we will get below screen which confirms that we are ready to use Fedora 29. Click on “Start Using Fedora”

#linux installation #fedora

Shell & Shell Scripting

Shell is the medium or intermediator between the user and computer and act as an form of wrapper around the Operating system hence termed Shell. It helps the user to connect with the system kernels to perform huge and various task hence the shell scripting is needed. Shell interpret the commands that acts as an interface for the access to operating system services such as Unix, Linux, Windows etc. Shell is the layer of programing on the outermost layer of the operating system which interprets commands and send necessary system calls to the kernel for execution of program. Today, there are many shells avavilable like bash, bsh, ksh, csh, zsh powershell etc. Among all the shells “bash” is the most and frequently used shell world wide. Shell is capable of automate very complex sequences of commands and most linux system are designed to be updated from typed in commands i.e. from shell. Shell also powers many of graphical commands that is run by users. Shell plays the most important role to better understand the computer. See below figure to better understand.

Linux Shell Shell classified in two categories. ⦁ Command Line Shell ⦁ Graphical shell

Command Line Shell:- Shell can be accessed by user using command line interface i.e. called Terminal in linux or Unix operating System. And Command Prompt in Windows operating System. Shell takes commands by user and call operating system to run those commands. For Example: ls, ls -a, cat, etc.

Graphical Shell:- Graphical shells provide means for manipulating programs based on graphical user interface (GUI), by allowing for operations such as opening, closing, moving and resizing. Shell Scripting

Usually, shells accepts commands as input from users and execute them. But sometimes we need to perform multiple operations using several commands hence to perform these operations we have to type all commands one by one to get the result. So to avoid repetitive work and run all commands at once we need Shell Scripting. In Shell scipting we group number of commands in a file, and when you run shell script file, shell will executes the commands in the script file order. A shell script have syntax just like any other programming language. Shell scripts consist below mention elements:- ⦁ Shell Keywords ⦁ Shell commands ⦁ Functions

Advantages of Shell & Shell Scripting ⦁ Shell can automate very complex sequences of commands. ⦁ Shell allows you to create new commands using other commands. ⦁ Scripting helps you to add new functions easily to the shell. ⦁ Writing shell scripts are much quicker and easier. ⦁ Interactive Debugging.

Disadvantages of Shell &Shell Scripting ⦁ Graphical environment is not userfriendly which is why scripting is being used less. ⦁ Provide minimal data Structures.

At last we must say, learning the Shell Scripting can help you better understand your computer.

#shell script #shell scripting #bash

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