C code compiled into an executable procedure

C code compiled into executable code through the compiler, went through four stages, in order: preprocessing, compiling, compiling, linking.

The next step is to explain each stage in detail

First, pretreatment

1. Tasks: Macro definition expansion, header file expansion, conditional compilation, no check syntax.

2. Command: GCC-E [source file]-o [preprocess file]

3, Case: Using the GCC compiler preprocessing demo1.c code, pre-processed text into the demo1.i. (GCC-E demo1.c-o demo1.i)

The DEMO1.C code is as follows:

1#include <stdio.h>2 3 #defineAdd (A, b) (A + B)4 #defineSub (A, b) (a A)5 6 intMainvoid)7 {8     intA, B, C, D;9 #ifndef __cplusplusTenA = b = c = d =1; One #else AA = b = c = d =2; - #endif -printf"num =%d\n", Sub (add (A, B), add (c, D))); the     return 0; -}

demo1.c

The generated demo1.i code is as follows:

1#1 "demo.c"2#1 "<command-line>"3#1 "/usr/include/stdc-predef.h" 1 3 44#1 "<command-line>" 25 6 omit 800 lines here ...7 8 extern voidFunlockfile (FILE *__stream) __attribute__ ((__nothrow__, __leaf__));9#943 "/usr/include/stdio.h" 3 4Ten  One#2 "demo.c" 2 A  -  - intMainvoid) the { -     intA, B, C, D; -  -A = b = c = d =1; +  -  +  Aprintf"num =%d\n", ((A + B)-(C +( D) )); at     return 0; -}

demo1.i

The case can be found: #define宏定义, stdio.h header file, #ifdef条件编译都被替换了, and you can deliberately write a syntax error code, but do not error. Because the stdio.h header file is more than 800 lines long, only a few lines at the beginning and end of the demo1.i are truncated.

　　　　

Second, compile

1, Task: Check the syntax, the pre-processed files compiled to generate assembly files.

2. Command: gcc-s [source file]-o [assembly file]

3, case; Compile the demo2.c code with the GCC compiler and put the compiled assembly code into DEMO2.S. (Gcc-s demo2.c-o Demo2.s)

The DEMO2.C code is as follows:

1 #include <stdio.h>23int main (intChar *argv[])  4{5     printf ("Hello world\n"); 6     return 0 ; 7 }

demo2.c

The generated DEMO2.S code is as follows:

1. file"demo2.c"2 . Section. Rodata3.LC0:4. String"Hello World"5 . Text6 . Globl Main7 . Type Main, @function8 Main:9.LFB0:Ten . Cfi_startproc One Pushq%RBP A. cfi_def_cfa_offset - -. cfi_offset6, - - - movq%rsp,%RBP the. cfi_def_cfa_register6 -SUBQ $ -,%RSP -MOVL%edi,-4(%RBP) -Movq%rsi,- -(%RBP) + MOVL $. LC0,%edi -     Pagerputs +MOVL $0,%eax A     Leave at. CFI_DEF_CFA7,8 -     ret - . Cfi_endproc -.LFE0: - . Size main,.-main -. ident"GCC: (Ubuntu 4.8.2-19ubuntu1) 4.8.2" in. section. Note. Gnu-stack,"", @progbits

Demo.s

We can see from the case that the C code we wrote was compiled into the assembly code. Intentionally write wrong A grammar point, the compiler will error.

III. compilation

1. Task: Generate the assembly file to the target file (2 binary file).

2. Command: gcc-s [source file]-o [target file]

3. Case: Compile demo3.c code with GCC compiler and put the compiled binary code into DEMO3.O. (Gcc-c demo3.c-o demo3.o)

The DEMO3.C code is as follows:

1 #include <stdio.h>23int main (intChar *argv[])  4{5     printf ("Hello world\n"); 6     return 0 ; 7 }

demo3.c

The generated DEMO3.O code is as follows:

Through the assembly phase, the text code becomes the binary code, which is the code that the computer can recognize. In the C language, the binary code file is suffixed with. O.

Iv. Links

1. Task: Locate the dependent library file and link the target file to the executable program.

2. Command: gcc-c [target file]-o [executable program]-l[Dynamic Library name]

3, Case: Through the GCC compiler let Demo4 link their own libadd.so dynamic library, and the Demo4 compiled into an executable program. GCC Demo4.c-o demo4-l./-ladd

The DEMO4.C code is as follows:

1#include <stdio.h>2#include"add.h"3 4 intMainintargcChar*argv[])5 {6printf"add =%d\n", Add (1,1));7     return 0;8}

demo4.c

To view the executable program information through the file command:

Run Result: add = 2

You can also view the size of the program's text segment, data segment, and BSS segment with the "Size [executable program]" command.

Before the program is run, we can determine the size of its text, data, and BSS segments.

C code compiled into an executable procedure