程序的安装
如果使用的是tar包安装. valgrind
# wget http://valgrind.org/downloads/valgrind-3.9.0.tar.bz2
# tar -jxvf valgrind-3.9.0.tar.bz2
# cd valgrind-3.9.0
# ./autogen.sh
# ./configure
# make; make install
使用命令：
valgrind --tool=memcheck --leak-check=full --show-reachable=yes --log-file=./valgrind.log.`date +%m%d%s` ./gameserver
如果后台起的话，也可以使用：
nohup valgrind --tool=memcheck --leak-check=full --show-reachable=yes --log-file=./valgrind.log.`date
+%m%d%s` ./gameserver &
error specification
一、有malloc，但未free
- code
- #include <stdio.h>
- #include <stdlib.h>
- void main()
- {
- char *p
= malloc(20); - sprintf(p,"%s","test");
- fprintf(stderr,"p:%s\n", p);
- }
- 分析：
文件后部，总体来看，有确定无疑的lost 20字节。如下：
- ==26512== LEAK SUMMARY:
- ==26512== definitely lost: 20 bytesin
1 blocks.
在文件之前描述的内容，细节可以看出，有1个malloc，但未去free。如下：
- ==26512==ERROR SUMMARY:
0 errors from 0 contexts(suppressed: 11 from 1) - ==26512== malloc/free:in
use at exit: 20 bytes
in 1 blocks. - ==26512== malloc/free:
1 allocs, 0 frees, 20 bytes allocated.
二、free一个未malloc的指针
- code
- void main()
- {
- char p[]=
"hello"; - fprintf(stderr,"p:%s\n", p);
- free(p);
- }
- 分析：
文件后部，总体来看，有1个错误，0个malloc，1个free。如下：
- ==26786==ERROR SUMMARY:
1 errors from 1 contexts(suppressed: 11 from 1) - ==26786== malloc/free:in
use at exit: 0 bytes
in 0 blocks. - ==26786== malloc/free:
0 allocs, 1 frees, 0 bytes allocated.
在文件之前描述的内容，细节可以看出，有一个无效的free。如下：
- ==26786== Invalid free()/
delete / delete[] - ==26786== at 0x402265C: free(vg_replace_malloc.c:323)
- ==26786== by 0x804841F: main(in/home/eric/workspace/valgrind/test/a.out)
- code
- void main()
- {
- char p[8]=
"hello";//p在栈上，"hello"在常量区 - fprintf(stderr,"p10:%c\n", p[10]);
- }
分析：
读取stack栈中的内容，不会提示错误
- ==27452==ERROR SUMMARY:
0 errors from 0 contexts(suppressed: 11 from 1) - ==27452== malloc/free:in
use at exit: 0 bytes
in 0 blocks. - ==27452== malloc/free:
0 allocs, 0 frees, 0 bytes allocated.
其为局部变量，存贮在stack中，由于p[10]未超出栈的长度，所以没提示出错
四、heap堆中，无效的读取，会提示出错
- code
- void main()
- {
- char *p
= malloc(8); - fprintf(stderr,"p10:%c\n", p[10]);
- free(p);
- }
- 分析：
读取heap堆中的内容，会提示错误，提示无效的1个字节的读取，位置是malloc的8字节的后面第2字节
- ==27744== Invalid read of size 1
- ==27744== at 0x804842A: main(in/home/eric/workspace/valgrind/test/a.out)
- ==27744== Address 0x4190032is 2 bytes after a block of
size 8 alloc'd - ==27744== at 0x4022AB8: malloc(vg_replace_malloc.c:207)
- ==27744== by 0x8048420: main(in/home/eric/workspace/valgrind/test/a.out)
- ==27744==
- ==27744==ERROR SUMMARY:
1 errors from 1 contexts(suppressed: 11 from 1) - ==27744== malloc/free:in
use at exit: 0 bytes
in 0 blocks. - ==27744== malloc/free:
1 allocs, 1 frees, 8 bytes allocated.
malloc的数据在heap堆中。
五、stack上的，无效的写
- code
- void main()
- {
- char p[8]=
"hello"; - p[10]='a';
- }
- 分析：
运行时会出错，会打印Backtrace
- *** stack smashing detected***:./a.out
terminated - =======
Backtrace:
========= - /lib/tls/i686/cmov/libc.so.6(__fortify_fail+0x48)[0x412d138]
- /lib/tls/i686/cmov/libc.so.6(__fortify_fail+0x0)[0x412d0f0]
- ./a.out[0x80483d6]
- /lib/tls/i686/cmov/libc.so.6(__libc_start_main+0xe0)[0x4056450]
- ./a.out[0x8048331]
- =======
Memory map:
======== - 04000000-0401a000 r-xp 00000000 08:06 682589/lib/ld-2.7.so
总体，会提示有1个错误，内容是5个malloc，0个free
- ==27918==ERROR SUMMARY:
1 errors from 1 contexts(suppressed: 13 from 1) - ==27918== malloc/free:in
use at exit: 892 bytes
in 5 blocks. - ==27918== malloc/free:
5 allocs, 0 frees, 892 bytes allocated. - ==27918== LEAK SUMMARY:
- ==27918== definitely lost: 0 bytesin
0 blocks. - ==27918== possibly lost: 0 bytesin
0 blocks. - ==27918== still reachable: 892 bytesin
5 blocks.
文件前面的错误信息是，有一个无效read，读了4个字节。
- ==27918== Invalid read of size 4
- ==27918== at 0x40151F3:(within
/lib/ld-2.7.so) - ==27918== by 0x4005C69:(within
/lib/ld-2.7.so) - ==27918== by 0x4007A97:(within
/lib/ld-2.7.so) - ==27918== by 0x4011543:(within
/lib/ld-2.7.so) - ==27918== by 0x400D5D5:(within
/lib/ld-2.7.so) - ==27918== by 0x4010F5D:(within
/lib/ld-2.7.so) - ==27918== by 0x414E291:(within
/lib/tls/i686/cmov/libc-2.7.so) - ==27918== by 0x400D5D5:(within
/lib/ld-2.7.so) - ==27918== by 0x414E454: __libc_dlopen_mode(in/lib/tls/i686/cmov/libc-2.7.so)
- ==27918== by 0x412A4D8:(within
/lib/tls/i686/cmov/libc-2.7.so) - ==27918== by 0x412A4D8:(within
/lib/tls/i686/cmov/libc-2.7.so) - ==27918== by 0x412A669: backtrace(in/lib/tls/i686/cmov/libc-2.7.so)
- ==27918== by 0x40A3B91:(within
/lib/tls/i686/cmov/libc-2.7.so) - ==27918== Address 0x4190038is 16 bytes inside a block
of size 19 alloc'd
这个提示的错误信息和代码中的信息，没很好的匹配上，但可以知道是已经出错了。
六、heap堆上，无效的写
- code
- void main()
- {
- char *p
= malloc(8); - p[10]='a';
- free(p);
- }
- 分析：
程序运行不会出错
写heap堆中的内容，log会提示错误，提示无效的1个字节的写，位置是malloc的8字节的后面第2字节
- ==28351== Invalid write of size 1
- ==28351== at 0x80483CA: main(in/home/eric/workspace/valgrind/test/a.out)
- ==28351== Address 0x4190032is 2 bytes after a block of
size 8 alloc'd - ==28351== at 0x4022AB8: malloc(vg_replace_malloc.c:207)
- ==28351== by 0x80483C0: main(in/home/eric/workspace/valgrind/test/a.out)