c module system
DESCRIPTION
C Module System. C and Data Structures Baojian Hua [email protected]. Software Systems are Large. Practical software systems tend to be large and complex: Linux kernel consists of ~1000K LOC So the general principals in designing large (even small) software systems are: - PowerPoint PPT PresentationTRANSCRIPT
Software Systems are Large
Practical software systems tend to be large and complex: Linux kernel consists of ~1000K LOC
So the general principals in designing large (even small) software systems are: dividing into manageable smaller ones separating specification (interface) from
code (implementation)
Module System
Module systems offer a systematic method to organize software Different parts can be separately
developed, compiled, tested, debugged Different parts are finally linked
together This process evolves compiling,
linking and libraries, etc.
Module System Different styles of module systems in
languages: ML signature and structure Java interface and class C (C++) header files (.h) and C files (.c)
This slide shows how to manage C’s module system: source programs (separate) compiling, linking, loading and tools
Typical C Program Organization
Program
file1
function1 functionm ……
… filen
function1 functionn
dec & stm
exp
dec & stm
exp
dec & stm
exp
dec & stm
exp
General Process// General process from source files (.c) to
// executables (.exe):
1.c
2.c
n.c
1.i
2.i
n.i
1.o
2.o
n.o
libraries
a.exe
preprocessing
Compiling
linking
… … …
Example Revisiteddouble area (int r);
double area (int r){ double pi = 3.14; return (pi*r*r);}
int main(){ double f; f = area(5); return 0;}
First Try// main.c
int main (){ double f; f = area (5); return 0;}
// area.cdouble area (int r);
#define PI 3.14double area (int r){ double f = PI *r *r; return f;}
Try this demo!
Wrong result? Why? Or even worse? f = area(5, 6, 7, 8, 9);
Second Try// main.cdouble area (int r);
int main (){ double f; f = area (5); return 0;}
// area.cdouble area (int r);
#define PI 3.14double area (int r){ double f = PI *r *r; return f;}
Try this demo!
Is this perfect? What about here is 10000 files contains “area” and “area.c” being changed?
Third Try
// area.hdouble area (int r);
// main.c#include “area.h”
int main () …
// area.c#include “area.h”
#define PI 3.14double area (int r){ double f = PI *r *r; return f;}
Try this demo!
Is this perfect!?
Pitfalls
// area.hdouble area (int r);int i = 0;
// main.c#include “area.h”
int main () …
// area.c#include “area.h”
#define PI 3.14double area (int r){ double f = PI *r *r; return f;}
Try this demo!
Final Version
// area.h#ifndef AREA_H#define AREA_H
double area (int r);
#endif
// main.c#include “area.h”…
// area.c#include “area.h”
#define PI 3.14double area (int r){ double f = PI *r *r; return f;}
Preprocessing Take source files (.c .h), generate
intermediate files file inclusion Macro substitution comments removal … afterwards, no header file needed any more
So, what’s the role of “.h” files?
Example
// area.h#ifndef AREA_H#define AREA_H
double area (int r);
#endif
// main.c#include “area.h”int main () { area (5);}
// area.c#include “area.h”
#define PI 3.14double area (int r){ double f = PI*r*r; return f;}
Example
// area.h#ifndef AREA_H#define AREA_H
double area (int r);
#endif
// main.c#include “area.h”int main () { area (5);}
// area.cdouble area (int r);
#define PI 3.14double area (int r){ double f = PI*r*r; return f;}
Example
// area.h#ifndef AREA_H#define AREA_H
double area (int r);
#endif
// main.c#include “area.h”int main () { area (5);}
// area.cdouble area (int r);
#define PI 3.14double area (int r){ double f = 3.14*r*r; return f;}
Example
// area.h#ifndef AREA_H#define AREA_H
double area (int r);
#endif
// main.cdouble area(int r);int main () { area (5);}
// area.cdouble area (int r);
double area (int r){ double f = 3.14*r*r; return f;}
Example
// area.h#ifndef AREA_H#define AREA_H
double area (int r);
#endif
// main.cdouble area(int r);int main () { area (5);}
// area.cdouble area (int r);
double area (int r){ double f = 3.14*r*r; return f;}
Compiling
Generate binary object files (.obj) object files in assembly or binary may involve several intermediate phases
analysis optimizations …
See demo …
Example
// main.cdouble area(int r);int main () { area (5);}
// area.cdouble area (int r);
double area (int r){ double f = 3.14*r*r; return f;}
// area.o010100101010010110100101001010010100101010101010
// main.o110101010010100110101001001010010001001001010010
Linking
Object files often called relocatable they are incomplete
function names, extern variables, etc. Linking the process of linking all objec
t files together resolve reference to external entities
See demo …
Linking// Object files are incomplete:
// main.o
area(…)printf(…)
Linking// Resolve external references:
// main.o
call areacall printf
// area.o
area:…
// printf.o
printf:…
Example
// main.cdouble area(int r);int main () { area (5);}
// area.cdouble area (int r);
double area (int r){ double f = 3.14*r*r; return f;}
// area.o010100101010010110100101001010010100101010101010
// main.o110101010010100110101001001010010001001001010010
// a.exe010101101……………
Static vs Dynamic Linking Static: all object files must be available and
link together the generated .exe files are complete what’s the pros and cons?
Dynamic: some object files are absent the generated .exe files are incomplete then how these absent object files are reference
d? what’s the pros and cons?
What are Libraries? Libraries just are pre-written pre-compiled
object files Normally offered by the compiler company
For user program linking purpose Header files are available
Ex: stdio.h, stdlib.h, ctype.h, …, from C standard library
Source code available (ex: gcc), or unavailable (ex: vc)
Same linking technique, but …
How to Implement Libraries?
In order to familiarize you with libraries implementation techniques and others, we next study carefully an example stdio.h
Our goal is to study the “printf” function
int printf (const char *format, …);
General Strategy User program call the library f
unction printf () printf () internally makes oper
ating system call to do the real work details vary on different OS
OS calls hardware driver Offered by hardware company
user program
libraries:printf()
OSroutines
hardwaredriver
Case Study: Linux vs Windows fwrite ()
user program
write ()int 0x80
sys_write ()Kernel
fwrite ()user program
write ()
NtWriteFile ()int 0x2e
IoWriteFile ()Kernel
API & SDK Application programming interface (API)
a set of routines that nicely wrap up operating system calls
libraries are built on top of them standard C libraries, runtime, etc.
Why API? Software Development Kit (SDK)
A collection of APIs header, libraries, files, and tools
Varies on different Windows version
Runtime
Runtime is a special set of libraries For program startup and exit get system info libraries preparation, etc. Normally NOT for called by user
program Again, vary between different
systems