linux programming

Tuesday, December 29, 2015

Linux programming

By Phu Le

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Makefile

What is a makefile?

Static library and Shared library

Assembler, Compiler, Linker and Loader

system() function

Contents


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Overview: Development process

Creation of source files (.c, .h, .cpp) Compilation (e.g. *.c *.o) and linking Running and testing programs

Makefile: What is makefile?


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d.hd.cppd.bj

Object files contain

machine code but not

in executable form.

Object files contain

references (calls) to

external functions that

must be resolved.

Linker programs are

commonly invoked by

(C/C++) compilers

Separate Compilation Steps

Step 1

source files compiled

to object files

Step 2

objects files

linked to form

executable

file.exe

a.h

a.cpp

a.obj

b.h

b.cpp

b.obj

c.h c.cpp c.obj

Overview: Development process


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Compilation (e.g. *.c *.o) and linking

Compilers (e.g. gcc, g++)

Automatic building tools (e.g. make)

Running and testing programs

Debuggers (e.g. gdb)

Compiling with g++:

g++ hello.cpp (compile hello.cpp, produce executable a.out)

g++ -o hello hello.cpp other_fns.cpp (compile hello.cpp and

other_fns.cpp, produce executable hello)

Overview


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From any source file, you can produce an object file to be

linked in later to an executable

g++ -c hello.cpp

g++ -c other_fuxnctions.cpp

g++ -o hello hello.o other_functions.o

Overview


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With medium to large software projects containing many

files, its difficult to:

Type commands to compile all the files correctly each

time

Keep track of which files have been changed

Keep track of files dependencies on other files

Problems


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The make utility automates this process

automatically builds executable programs from source

code by reading makefiles.

Make Utility


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Makefiles:

files consisting of rules and dependencies that specify how

to build (or make) a target program.

can make the compilation procedure much faster.

The compilation is done using a single command

Only the files that must be compiled are compiled

Allows managing large programs with a lot of dependencies.

Makefile: What is makefile?


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PyCal: Makefile Example


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PyCal: Makefile Example


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Contains objects code.

Linked with an end-user application.

A part of that executable.

/lib, /usr/lib or /usr/local/lib

Filenames: start with lib, end with .a

Static library


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Static library


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Build:

$ ar

$ ar --help

Options: c, r, v, V, T, ...

Example:

$ ar -crv libExpress.a Postfix.o Prefix.o Values.o

Static library


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Intended to be shared objects files.

into memory at load time or run time.

Rather than being copied by linker when it creates executable.

(static library)

Filenames: start with lib, end with .so

Shared Library


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Shared library


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Build:

the -fPIC option to object code file.

the -shared option to shared library file.

Example:

$ g++ -c -fPIC Express.cpp

$ g++ -shared -o libExpress.so Express.o

Shared Library


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Use:

LD_LIBRARY_PATH

$ export LD_LIBRARY_PATH=$ LD_LIBRARY_PATH: YOUR_DIRECTORY

/lib , /usr/lib, /usr/local/lib

-Wl,-rpath option

$ g++ main.o -L./LIB -lExpress -Wl,-rpath,./LIB

Shared Library


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$ nm to see more information of library

$ nm libExpress.so

$ nm libExpress.a

$ nm -help

Example:

$ nm libExpress.so

0000000000201058 B __bss_start

0000000000201058 b completed.6972

...

0000000000200df0 d _DYNAMIC

...

0000000000000a7c t _GLOBAL__sub_I_functions.cpp

0000000000000b53 t _GLOBAL__sub_I_sumfunctions.cpp

w __gmon_start__

Check Library


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$ ldd check the required shared libraries for a program to run.

$ ldd main

Example:

linux-vdso.so.1 => (0x00007fff829fe000)

libExpress.so =>

/usr/lib/libExpress.so(0x00007f2b68311000)

...

Check Library


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Static lib and Shared lib


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Compiler, Assember, Linker and Loader


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Translates high-level language program into assembly

language.

.s (lower case) Assembler source files.

Compiler


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Converts assembly language programs into object files

Object files contain a combination of machine instructions, data,

and information needed to place instructions properly in

memory.

*.a, *.o source file output.

Assember


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Typically, assemblers make two passes over the assembly file

First pass: reads each line and records labels in a symbol table.

Second pass: use info in symbol table to produce actual machine

code for each line.

Assember


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Tool that merges the object files produced by separate

compilation or assembly and creates an executable file.

*.out, *.exe source file output.

Linker


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Three tasks

Searches the program to find library routines used by

program, e.g. printf(), math routines,

Determines the memory locations that code from each

module will occupy and relocates its instructions by

adjusting absolute references

Resolves references among files.

Linker


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Part of the OS that brings an executable file residing on disk

into memory and starts it running.

Loader


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Steps

Read executable files header to determine the size of text and

data segments

Create a new address space for the program

Copies instructions and data into address space

Copies arguments passed to the program on the stack

Initializes the machine registers including the stack ptr

Jumps to a startup routine that copies the programs arguments

from the stack to registers and calls the programs main routine

Loader


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Loader


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Build:

g++ hello.cpp o hello

g++ -save-temps hello.cpp o hello



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execute a shell command.

#include

int system(const char *command);

The return value of system():

If a child process could not be created, or its status could not be

retrieved, the return value is -1.

If a shell could not be executed in the child process, the return

value is 127. (_exit(2)).

-1: The return value of system(string).

system() function


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http://eclipsebook.in/c-cpp-development/building-code/build-

eclipse-managed/

http://www.fotech.org/forum/index.php?showtopic=36504

http://vi.wikipedia.org/wiki/B%E1%BB%99_tr%C3%ACnh_d%E1%BB%8B

ch_GNU

http://www.adp-gmbh.ch/cpp/gcc/create_lib.html

http://www.ntu.edu.sg/home/ehchua/programming/cpp/gcc_make

.html

http://forum.gocit.vn/threads/gioi-thieu-gcc.158/

http://vi.wikipedia.org/wiki/GNU_Debugger

References


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http://lttqstudy.wordpress.com/2011/08/22/ham-trong-cc/

http://www.mingw.org/wiki/sampledll

http://www.adp-gmbh.ch/cpp/gcc/create_lib.html

http://www.ntu.edu.sg/home/ehchua/programming/cpp/gcc_make

.html

http://ftp.gnu.org/old-gnu/Manuals/make-

3.79.1/html_chapter/make_9.html

http://web.mit.edu/gnu/doc/html/make_5.html

References


Welcome Your Questions!

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