DEBUG and optimization of GCC in Linux and the compilation process

1: DEBUG instance [root @ localhostdebug] # vimnull. cinta (int * p); intmain (void) {int * p0; returna (p);} inta (int * p) {inty * p; returny ;}~ [Root @ localhostdebug] # ulimit-cunlimited [root @ localhostdebug] # gcc-Wall? Gnul

1. DEBUG instance

[Root @ localhost debug] # vim null. c

 

Int a (int * p );

 

Int main (voId)

{

Int * p = 0;

Return a (p );

}

Int a (int * p)

{

Int y = * p;

Return y;

}

~

[Root @ localhost debug] #Ulimit-C unlimitEd

[Root @ localhost debug] # gcc-Wall? G null. c

[Root @ localhost debug] #./a. out

Segmentation fault (coreDuMped)

[Root @ localhost debug] #Ls

Null. c a. out core.21982

[Root @ localhost debug] # yum-y install gdb

[Root @ localhost debug] # gdb a. out core.21982

.................

.................

.................

(Gdb) print p

No symbol table is loaded. Use"File"Command.

(Gdb) print p

$1 = (int *) 0x0

(Gdb) backTrAce

#0 0x08048389 in a (p = 0x0) at null. c: 10

#1 0x08048377 in main () at null. c: 6

(Gdb) quit (gdb)

Second: optimize the instance (here the main use of-O0-3 and no-loops)

[Root @ localhost opm] #CatTest. c

# INcLude

 

Double powern (double d, unsigned n)

{

Double x = 1.0;

Unsigned j;

 

For (j = 1; j

X * = d;

Return x;

}

 

Int main (void)

{

DoubleSuM = 0.0;

Unsigned I;

 

For (I = 1; I <= 100000000; I ++)

{

Sum + = powern (I, I % 5 );

}

Printf ("sum = % g \ n", sum );

Return 0;

}

[Root @ localhost opm] # gcc-Wall-O0 test. c-o o0 // The optimization level is 0-not optimized

[Root @ localhost opm] #Time./O0

Sum = 5e + 30

 

Real 0m2. 815 s

User 0m2. 799 s

Sys 0m0. 013 s

[Root @ localhost opm] # gcc-Wall-O1 test. c-o o1 // The optimization level is 1.

[Root @ localhost opm] # time./o1

Sum = 5e + 30

 

Real 0m1. 849 s

User 0m1. 843 s

Sys 0m0. 006 s

[Root @ localhost opm] # gcc-Wall-O2 test. c-o o2 // The optimization level is 2.

[Root @ localhost opm] # time./o2

Sum = 5e + 30

 

Real 0m1. 923 s

User 0m1. 910 s

Sys 0m0. 011 s

[Root @ localhost opm] # gcc-Wall-O3 test. c-o o3 // The optimization level is 1.

[Root @ localhost opm] # time./o3

Sum = 5e + 30

 

Real 0m1. 460 s

User 0m1. 453 s

Sys 0m0. 006 s

[Root @ localhost opm] # gcc-Wall-O3-funroll-loops test. c-o o4 // Add no-loop Optimization

[Root @ localhost opm] # time./o4

Sum = 5e + 30

 

Real 0m1. 322 s

User 0m1. 308 s

Sys 0m0. 014 s

Third: optimize and help to discover DEBUG

[Root @ localhost O] # vim uninit. c

 

Int sign (int x)

{

Int s;

If (x> 0)

S = 1;

Else if (x <0)

S =-1;

Return s;

}

[Root @ localhost O] # gcc-Wall-c uninit. c

[Root @ localhost O] # gcc-Wall-O1-c uninit. c

Uninit. c: In function 'sign ':

Uninit. c: 3: warning:'s 'may be uSedUninitialized in this function

[Root @ localhost O] # gcc-Wall-O2-c uninit. c

Uninit. c: In function 'sign ':

Uninit. c: 3: warning:'s 'may be used uninitialized in this function

[Root @ localhost O] # gcc-Wall-O3-c uninit. c

Uninit. c: In function 'sign ':

Uninit. c: 3: warning:'s 'may be used uninitialized in this function

Compile Process Description Example

[Root @ localhost hello] # vim hello. c

 

# Include

 

Int main (void)

{

Printf ("Hello World !!! \ N ");

Return 0;

}

4. Finally, list the compiled process instances.

1. pre-processor stage (CpP hello. c> hello. I)

[Root @ localhost hello] # cpp hello. c> hello. I

2. compiler stage (gcc-Wall-S hello. I)

[Root @ localhost hello] # gcc-Wall-S hello. I

3. assembler stage (as hello. s-o hello. o)

[Root @ localhost hello] # as hello. s-o hello. o

4. connector stage (gcc hello. o)

[Root @ localhost hello] # gcc hello. o

[Root @ localhost hello] #./a. out

Hello World !!!

[Root @ localhost hello] # file a. out // check the information of the executable file

A. out: ELF 32-bit LSBExECutAble, Intel 80386, version 1 (SYSV), for GNU/Linux 2.6.9, dynamically linked (uses shared libs), for GNU/Linux 2.6.9, not stripped

[Root @ localhost hello] # lDdA. out // check the library files used

Linux-gate.so.1 => (0x002ab000)

Libc. so.6 =>/lib/libc. so.6 (0x00b3a000)

/Lib/ld-linux.so.2 (0x00b17000)

End

Summary: This article is a note for instructor Xiao Bu's video teaching, in order to deepen his memory and record it.