What is compiler linker loader

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I wanted to know in depth meaning and working of compiler  linker and loader  With reference to any language preferably c

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compiler changes checks your source code for errors and changes it into object code.this is the code that operating system runs.

You often don't write a whole program in single file so linker links all your object code files.

your program wont get executed unless it is in main memory

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Compiler It converts the source code into the object code   Linker It combines the multiple object files into a single executable program file   Loader It loads the executable file into main memory

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Compiler   It will read source file which may be of type  c or  cpp etc and translates  that to  o file called as object file   Linker   It combines the several  o files which may be generated for multiple source files into an executable file  ELF format in GCC   There are two type of linking    static linking dynamic linking   Loader   A program which loads the executable file to the primary memory of the machine     For an in-detail study about the these three stages of program execution in Linux  please read this

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A compiler is a special program that processes statements written in a particular programming language and turns them into machine language or  code  that a computer s processor uses

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Compiler  it is a system software which correct the error of programs object file  messages etc  Linker it is a system software which combines One or more objectfiles and possible some library code into either some exicutable some library or a list of error  Loader   A program which loads the executable file to the primary memory of the machine

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Compiler  It is a program which translates a high level language program into a machine language program  A compiler is more intelligent than an assembler  It checks all kinds of limits  ranges  errors etc  But its program run time is more and occupies a larger part of the memory  It has slow speed  Because a compiler goes through the entire program and then translates the entire program into machine codes  If a compiler runs on a computer and produces the machine codes for the same computer then it is known as a self compiler or resident compiler  On the other hand  if a compiler runs on a computer and produces the machine codes for other computer then it is known as a cross compiler   Linker  In high level languages  some built in header files or libraries are stored  These libraries are predefined and these contain basic functions which are essential for executing the program  These functions are linked to the libraries by a program called Linker  If linker does not find a library of a function then it informs to compiler and then compiler generates an error  The compiler automatically invokes the linker as the last step in compiling a program  Not built in libraries  it also links the user defined functions to the user defined libraries  Usually a longer program is divided into smaller subprograms called modules  And these modules must be combined to execute the program  The process of combining the modules is done by the linker   Loader  Loader is a program that loads machine codes of a program into the system memory  In Computing  a loader is the part of an Operating System that is responsible for loading programs  It is one of the essential stages in the process of starting a program  Because it places programs into memory and prepares them for execution  Loading a program involves reading the contents of executable file into memory   Once loading is complete  the operating system starts the program by passing control to the loaded program code  All operating systems that support program loading have loaders  In many operating systems the loader is permanently resident in memory

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explained with respect to  linux unix based systems  though it s a basic concept for all other computing systems      Linkers and Loaders from LinuxJournal explains this concept with clarity   It also explains how the classic name a out came    assembler output   A quick summary   c program -- gt   compiler  -- gt  objectFile -- gt   linker  -- gt  executable file  say  a out   we got the executable  now give this file to your friend or to your customer who is in need of this software     when they run this software  say by typing it in command line   a out  execute in command line   a out  -- gt   Loader  -- gt   execve  -- gt  program is loaded in memory  Once the program is loaded into the memory  control is transferred to this program by making the PC  program counter  pointing to the first instruction of a out

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gt  COMPILATION PROCESS  lt                                                      ---- gt   Input is Source file  c                                              V                                                                               C Preprocessor                                                                                                                  --- gt  Pure C file   comd cc -E  lt file name gt                                                V                                                                               Lexical Analyzer                                               -----------------                                                Syntax Analyzer                                                -----------------                                                Semantic Analyze                                               -----------------                                                Pre Optimization                                               -----------------                                                Code generation                                                -----------------                                                Post Optimize                                                                                                                  --- gt   Assembly code  comd  cc -S  lt file name gt                                                V                                                                                 Assembler                                                                                                                    --- gt   Object file   obj   comd  cc -c  lt file name gt                                               V                                                   Linker                           and                            loader                                                                                     --- gt   Executable   Exe a out   com cc  lt file name gt                                                 V             Executable file a out    C preprocessor  -  C preprocessing is the first step in the compilation  It handles     define statements   include statements  Conditional statements  Macros   The purpose of the unit is to convert the C source file into Pure C code file   C compilation    There are Six steps in the unit    1   Lexical Analyzer   It combines characters in the source file  to form a  TOKEN   A token is a set of characters that does not have  space    tab  and  new line   Therefore this unit of compilation is also called  TOKENIZER   It also removes the comments  generates symbol table and relocation table entries   2   Syntactic Analyzer   This unit check for the syntax in the code  For ex         int a      int b      int c      int d       d   a   b - c           The above code will generate the parse error because the equation is not balanced  This unit checks this internally by generating the parser tree as follows                                                                                         d       -                                                                                                                                                     a       b   c           Therefore this unit is also called PARSER   3   Semantic Analyzer   This unit checks the meaning in the statements  For ex         int i      int  p       p   i      -----     -----     -----     The above code generates the error  Assignment of incompatible type    4   Pre-Optimization   This unit is independent of the CPU  i e   there are two types of optimization   Preoptimization  CPU independent  Postoptimization  CPU dependent    This unit optimizes the code in following forms    I  Dead code elimination II  Sub code elimination III  Loop optimization   I    Dead code elimination   For ex           int a   10      if   a  gt  5                                             else                                            Here  the compiler knows the value of  a  at compile time  therefore it also knows that the if condition is always true  Hence it eliminates the else part in the code   II   Sub code elimination   For ex         int a  b  c      int x  y                              x   a   b      y   a   b   c                             can be optimized as follows         int a  b  c      int x  y                               x   a   b      y   x   c          a   b is replaced by x                             III  Loop optimization   For ex         int a      for  i   0  i  lt  1000  i                                    a   10                                    In the above code  if  a  is local and not used in the loop  then it can be optimized as follows         int a      a   10      for  i   0  i  lt  1000  i                                                   5   Code generation   Here  the compiler generates the assembly code so that the more frequently used variables are stored in the registers   6   Post-Optimization   Here the optimization is CPU dependent  Suppose if there are more than one jumps in the code then they are converted to one as               -----         jmp  lt addr1 gt   lt addr1 gt  jmp  lt addr2 gt              -----             -----   The control jumps to the  directly   Then the last phase is Linking  which creates executable or library   When the executable is run  the libraries it requires are Loaded

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Compiler  A language translator that converts a complete program into machine language to produce a program that the computer can process in its entirety  Linker  Utility program which takes one or more compiled object files and combines them into an executable file or another object file  Loader  loads the executable code into memory  creates the program and data stack   initializes the registers and starts the code running

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A Compiler translates lines of code from the programming language into machine language   A Linker creates a link between two programs   A Loader loads the program into memory in the main database  program  etc

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Compiler   Which convert Human understandable format into machine understandable format Linker   Which convert machine understandable format into Operating system understandable format Loader   is entity which actually load and runs the program into RAM   Linker  amp  Interpreter are mutually exclusive Interpreter getting code line by line and execute line by line

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Wikipedia ought to have a good answer  here s my thoughts    Compiler  reads something c source  writes something o object  Linker  joins several   o files into an executable program  Loader  code that loads an executable into memory and starts it running

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Hope this helps you a little more  First  go through this diagram   img source- gt internet    You make a piece of code and save the file  Source code   then Preprocessing  - As the name suggests  it s not part of compilation  They instruct the compiler to do required pre-processing before the actual compilation  You can call this phase Text Substitution or interpreting special preprocessor directives denoted by    Compilation  - Compilation is a process in which a program written in one language get translated into another targeted language  If there is some errors  the compiler will detect them and report it  Assemble  - Assemble code gets translated into machine code  You can call assembler a special type of complier  Linking - If these piece of code needs some other source file to be linked  linker link them to make it a executable file  There are many process that happens after it  Yes  you guessed it right here comes the role of the loader  Loader - It loads the executable code into memory  program and data stack are created  register gets initialized  Little Extra info  - http   www geeksforgeeks org memory-layout-of-c-program    you can see the memory layout over there

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A compiler reads  analyses and translates code into either an object file or a list of error messages  A linker combines one or more object files and possible some library code into either some executable  some library or a list of error messages  A loader reads the executable code into memory  does some address translation and tries to run the program resulting in a running program or an error message  or both     ASCII representation    Source Code  --- gt  Compiler --- gt   Object code  --                                                      Source Code  --- gt  Compiler --- gt   Object code  -- -- gt  Linker -- gt   Executable  --- gt  Loader                                                                                           Source Code  --- gt  Compiler --- gt   Object code  --                                                                                                                                                                 Library file --                                     V                                                                         Running Executable in Memory

[compiler-construction] What is compiler, linker, loader?

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