1、linux下gcc的debug和優化，以及編譯過程int main(vo) int* p = 0; return a(p); int a(int *p) int y = *p; return y; rootlocalhost debug -c unlimit rootlocalhost debug gcc -wall g null.c rootlocalhost debug ./a.out segmentation fault (core mped) rootlocalhost debug null.c a.out core.21982 rootlocalhost debug yum -y i

2、nstall gdb rootlocalhost debug gdb a.out core.21982 . . . (gdb) print p no symbol table is loaded. use the command. (gdb) print p $1 = (int *) 0x0 (gdb) backace 0 0x08048389 in a (p=0x0) at null.c:10 1 0x08048377 in main () at null.c:6 (gdb) quit (gdb) 其次：優化實例(這里主要采納的是-o03和no-loops方式) rootlocalhost

3、opm test.c ilude stdio.h double powern(double d, unsigned n) double x = 1.0; unsigned j; for(j=1;j j+) x *=d; return x; int main(void) double m = 0.0; unsigned i; for(i=1;i =100000000;i+ ) sum += powern(i,i%5); printf( sum = %gn ,sum); return 0; rootlocalhost opm gcc -wall -o0 test.c -o o0 /優化等級為0-不

4、優化 rootlocalhost opm ./o0 sum = 5e+30 real 0m2.815s user 0m2.799s sys 0m0.013s rootlocalhost opm gcc -wall -o1 test.c -o o1 /優化等級為1 rootlocalhost opm time ./o1 sum = 5e+30 real 0m1.849s user 0m1.843s sys 0m0.006s rootlocalhost opm gcc -wall -o2 test.c -o o2 /優化等級為2 rootlocalhost opm time ./o2 sum =

5、5e+30 real 0m1.923s user 0m1.910s sys 0m0.011s rootlocalhost opm gcc -wall -o3 test.c -o o3 /優化等級為1 rootlocalhost opm time ./o3 sum = 5e+30 real 0m1.460s user 0m1.453s sys 0m0.006s rootlocalhost opm gcc -wall -o3 -funroll-loops test.c -o o4 /加入noloop優化 rootlocalhost opm time ./o4 sum = 5e+30 real 0m

6、1.322s user 0m1.308s sys 0m0.014s 第三：優化協助發覺debug rootlocalhost o vim uninit.c int sign(int x) int s; if (x 0) s = 1; else if (x 0) s = -1; return s; rootlocalhost o gcc -wall -c uninit.c rootlocalhost o gcc -wall -o1 -c uninit.c uninit.c: in function 'sign': uninit.c:3: warning: 's'

7、may be u uninitialized in this function rootlocalhost o gcc -wall -o2 -c uninit.c uninit.c: in function 'sign': uninit.c:3: warning: 's' may be used uninitialized in this function rootlocalhost o gcc -wall -o3 -c uninit.c uninit.c: in function 'sign': uninit.c:3: warning: 

8、9;s' may be used uninitialized in this function 編譯過程描述實例 rootlocalhost hello vim hello.c include stdio.h int main(void) printf( hello world!n return 0; 第四：最后列舉下編譯的過程實例 1、 預處理器階段（p hello.c hello.i） rootlocalhost hello cpp hello.c hello.i 2、 編譯器階段（gcc -wall -s hello.i） rootlocalhost hello gcc -wal

9、l -s hello.i 3、 匯編器階段（as hello.s -o hello.o） rootlocalhost hello as hello.s -o hello.o 4、 銜接器階段（gcc hello.o） rootlocalhost hello gcc hello.o rootlocalhost hello ./a.out hello world! rootlocalhost hello file a.out /檢測可執行文件的信息 a.out: elf 32-bit lsb eable, intel 80386, version 1 (sysv), for gnu/linux 2.6.9, dynamically linked (uses shared libs), for gnu/linux 2.6.9, not stripped rootlocalhost hello l a.out /檢查用到的庫文件 lin