Valgrind通常用来成分析程序性能及程序中的内存泄露错误
一 Valgrind工具集简绍
Valgrind包含下列工具:
1、memcheck:检查程序中的内存问题,如泄漏、越界、非法指针等。
2、callgrind:检测程序代码的运行时间和调用过程,以及分析程序性能。
3、cachegrind:分析CPU的cache命中率、丢失率,用于进行代码优化。
4、helgrind:用于检查多线程程序的竞态条件。
5、massif:堆栈分析器,指示程序中使用了多少堆内存等信息。
6、lackey:
7、nulgrind:
这几个工具的使用是通过命令:valgrand --tool=name 程序名来分别调用的,当不指定tool参数时默认是 --tool=memcheck
二 Valgrind工具详解
1.Memcheck
最常用的工具,用来检测程序中出现的内存问题,所有对内存的读写都会被检测到,一切对malloc、free、new、delete的调用都会被捕获。所以,它能检测以下问题:
1、对未初始化内存的使用;
2、读/写释放后的内存块;
3、读/写超出malloc分配的内存块;
4、读/写不适当的栈中内存块;
5、内存泄漏,指向一块内存的指针永远丢失;
6、不正确的malloc/free或new/delete匹配;
7、memcpy()相关函数中的dst和src指针重叠。
这些问题往往是C/C++程序员最头疼的问题,Memcheck能在这里帮上大忙。
例如:
#include <stdlib.h> #include <malloc.h> #include <string.h> void test() { int *ptr = malloc(sizeof(int)*10); ptr[10] = 7; // 内存越界 memcpy(ptr +1, ptr, 5); // 踩内存 free(ptr); free(ptr);// 重复释放 int *p1; *p1 = 1; // 非法指针 } int main(void) { test(); return 0; }
将程序编译生成可执行文件后执行:valgrind --leak-check=full ./程序名
输出结果如下:
==4832== Memcheck, a memory error detector ==4832== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al. ==4832== Using Valgrind-3.6.1 and LibVEX; rerun with -h for copyright info ==4832== Command: ./tmp ==4832== ==4832== Invalid write of size 4 // 内存越界 ==4832== at 0x804843F: test (in /home/yanghao/Desktop/testC/testmem/tmp) ==4832== by 0x804848D: main (in /home/yanghao/Desktop/testC/testmem/tmp) ==4832== Address 0x41a6050 is 0 bytes after a block of size 40 alloc'd ==4832== at 0x4026864: malloc (vg_replace_malloc.c:236) ==4832== by 0x8048435: test (in /home/yanghao/Desktop/testC/testmem/tmp) ==4832== by 0x804848D: main (in /home/yanghao/Desktop/testC/testmem/tmp) ==4832== ==4832== Source and destination overlap in memcpy(0x41a602c, 0x41a6028, 5) // 踩内存 ==4832== at 0x4027BD6: memcpy (mc_replace_strmem.c:635) ==4832== by 0x8048461: test (in /home/yanghao/Desktop/testC/testmem/tmp) ==4832== by 0x804848D: main (in /home/yanghao/Desktop/testC/testmem/tmp) ==4832== ==4832== Invalid free() / delete / delete[] // 重复释放 ==4832== at 0x4025BF0: free (vg_replace_malloc.c:366) ==4832== by 0x8048477: test (in /home/yanghao/Desktop/testC/testmem/tmp) ==4832== by 0x804848D: main (in /home/yanghao/Desktop/testC/testmem/tmp) ==4832== Address 0x41a6028 is 0 bytes inside a block of size 40 free'd ==4832== at 0x4025BF0: free (vg_replace_malloc.c:366) ==4832== by 0x804846C: test (in /home/yanghao/Desktop/testC/testmem/tmp) ==4832== by 0x804848D: main (in /home/yanghao/Desktop/testC/testmem/tmp) ==4832== ==4832== Use of uninitialised value of size 4 // 非法指针 ==4832== at 0x804847B: test (in /home/yanghao/Desktop/testC/testmem/tmp) ==4832== by 0x804848D: main (in /home/yanghao/Desktop/testC/testmem/tmp) ==4832== ==4832== ==4832== Process terminating with default action of signal 11 (SIGSEGV) //由于非法指针赋值导致的程序崩溃 ==4832== Bad permissions for mapped region at address 0x419FFF4 ==4832== at 0x804847B: test (in /home/yanghao/Desktop/testC/testmem/tmp) ==4832== by 0x804848D: main (in /home/yanghao/Desktop/testC/testmem/tmp) ==4832== ==4832== HEAP SUMMARY: ==4832== in use at exit: 0 bytes in 0 blocks ==4832== total heap usage: 1 allocs, 2 frees, 40 bytes allocated ==4832== ==4832== All heap blocks were freed -- no leaks are possible ==4832== ==4832== For counts of detected and suppressed errors, rerun with: -v ==4832== Use --track-origins=yes to see where uninitialised values come from ==4832== ERROR SUMMARY: 4 errors from 4 contexts (suppressed: 11 from 6) Segmentation fault从valgrind的检测输出结果看,这几个错误都找了出来。