标签：heap star eof .com sse parent 很多 tree 运行
1、问题
虽然C/C++是一种非常有用且功能强大的语言，但很难调试。 某些时候可能遇到内存错误。 我们已经用gdb，如果程序一直崩溃或出错，gdb可能是一个有用工具。 但是，有时遇到的问题是由于内存错误造成的，但它不导致段错误，并且不希望在gdb中设置很多断点逐步盘查。 还可能会遇到的另一个问题是内存泄漏：在某个地方，调用malloc分配的内存没有调用free来释放。 Valgrind是一个可以帮助解决这两个问题的程序
2、valgrind功能介绍
Valgrind是一个构建动态分析工具的工具框架，其带有一组工具，每个都执行某种调试，分析或类似的任务，可帮助开发者改进程序。 Valgrind的架构是模块化的，因此可以轻松创建新工具，而不会影响现有结构。标准提供了许多有用的工具。
在这里，我们主要讨论内存错误检测器(Memcheck)，用于检测C/C ++程序中常见问题：
像这些问题有时候很难通过其他方式发现，常常长时间未被发现，然后导致偶然的，难以诊断的崩溃。Memcheck还使用命令行选项--xtree-memory和monitor命令xtmemory，对执行树提供内存分析。
3、内存泄露
在这个例子中，释放缓存的逻辑已经被注释，所以产生一个内存泄露的问题。
#define SNPRINTF_ATTR(fmt_pos, firstarg_pos) \ __attribute__ ((format(vsnprintf, fmt_pos, firstarg_pos))) #include <stdio.h> #include <stdarg.h> #include <stdlib.h> using namespace std; class query_buffer { private: char *buf; size_t len; size_t cap; public: query_buffer(): len(0), cap(2048) { buf = (char *)calloc(cap, sizeof(char)); }; virtual ~query_buffer() { //if (buf) free(buf); len = 0; cap = 0; }; void resize_if_needed(size_t new_len) { if (new_len >= cap) { while (new_len > cap) cap *= 2; buf = (char *)realloc(buf, cap*sizeof(char)); } else if (4 * new_len < cap) { cap /= 2; buf = (char *)realloc(buf, cap*sizeof(char)); } }; int append(const char *fmt, ...) SNPRINTF_ATTR(3, 4) { //resize_if_needed(len + max_print_len); va_list args; va_start(args, fmt); int n = vsnprintf(buf + len, static_cast<int>(cap - len), fmt, args); if (n>=0) len += n; va_end(args); return n; }; const char *get_buf() { return this->buf; }; }; int main(void) { query_buffer query_buffer; query_buffer.resize_if_needed(256); int n = query_buffer.append("%d: %s -- %s, %s\n", 1, "engineer", "office", "computer?"); n += query_buffer.append("%d: %s -- %s, %s\n", 2, "chef", "kitchen", "oven?"); n += query_buffer.append("%d: %s -- %s, %s\n", 3, "gardener", "yard", "yard?"); n += query_buffer.append("%d: %s -- %s, %s\n", 4, "nurse", "hospital", "patient?"); printf("Total size %d:\n%s", n, query_buffer.get_buf()); }
编译后，运行程序querybuf：
valgrind --tool=memcheck --leak-check=yes --show-reachable=yes --num-callers=20 --track-fds=yes ./querybuf
==74342== Memcheck, a memory error detector ==74342== Copyright (C) 2002-2013, and GNU GPL‘d, by Julian Seward et al. ==74342== Using Valgrind-3.10.0 and LibVEX; rerun with -h for copyright info ==74342== Command: ./a.out ==74342== Total size 205: 1: engineer -- office, (what wrong with the computer?) 2: chef -- kitchen, (what wrong with the oven?) 3: gardener -- yard, (what wrong with the yard?) 4: nurse -- hospital, (what wrong with the patient?) ==74342== ==74342== FILE DESCRIPTORS: 3 open at exit. ==74342== Open file descriptor 2: /dev/pts/2 ==74342== <inherited from parent> ==74342== ==74342== Open file descriptor 1: /dev/pts/2 ==74342== <inherited from parent> ==74342== ==74342== Open file descriptor 0: /dev/pts/2 ==74342== <inherited from parent> ==74342== ==74342== ==74342== HEAP SUMMARY: ==74342== in use at exit: 1,024 bytes in 1 blocks ==74342== total heap usage: 2 allocs, 1 frees, 3,072 bytes allocated ==74342== ==74342== 1,024 bytes in 1 blocks are definitely lost in loss record 1 of 1 ==74342== at 0x4C2BB4A: realloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so) ==74342== by 0x400B38: query_buffer::resize_if_needed(unsigned long) (tryvarargs.cpp:32) ==74342== by 0x4008B5: main (tryvarargs.cpp:53) ==74342== ==74342== LEAK SUMMARY: ==74342== definitely lost: 1,024 bytes in 1 blocks ==74342== indirectly lost: 0 bytes in 0 blocks ==74342== possibly lost: 0 bytes in 0 blocks ==74342== still reachable: 0 bytes in 0 blocks ==74342== suppressed: 0 bytes in 0 blocks ==74342== ==74342== For counts of detected and suppressed errors, rerun with: -v ==74342== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 2 from 2)
从上述报错信息可知，realloc的内存没有释放造成内存泄露。这指向释放realloc分配内存的地方有问题--〉类的destructor。
4、读写过界
下面例子有两个问题：
int main(void) { char *buf = (char *)calloc(10, sizeof(char)); for (int i = 0; i < 11; ++i) buf[i] = static_cast<char>(‘a‘ + i); printf("%s", buf); delete buf; }
valgrind --tool=memcheck ./heapoverflow
==101781== Memcheck, a memory error detector ==101781== Copyright (C) 2002-2013, and GNU GPL‘d, by Julian Seward et al. ==101781== Using Valgrind-3.10.0 and LibVEX; rerun with -h for copyright info ==101781== Command: ./heapoverflow ==101781== ==101781== Invalid write of size 1 ==101781== at 0x400A3B: main (tryvarargs.cpp:66) ==101781== Address 0x5a1304a is 0 bytes after a block of size 10 alloc‘d ==101781== at 0x4C2B974: calloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so) ==101781== by 0x400A1A: main (tryvarargs.cpp:63) ==101781== ==101781== Invalid read of size 1 ==101781== at 0x569CA94: vfprintf (in /usr/lib64/libc-2.17.so) ==101781== by 0x56A5C18: printf (in /usr/lib64/libc-2.17.so) ==101781== by 0x400A5C: main (tryvarargs.cpp:68) ==101781== Address 0x5a1304a is 0 bytes after a block of size 10 alloc‘d ==101781== at 0x4C2B974: calloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so) ==101781== by 0x400A1A: main (tryvarargs.cpp:63) ==101781== ==101781== Invalid read of size 1 ==101781== at 0x56CD4FE: _IO_default_xsputn (in /usr/lib64/libc-2.17.so) ==101781== by 0x56CB551: _IO_file_xsputn@@GLIBC_2.2.5 (in /usr/lib64/libc-2.17.so) ==101781== by 0x569CA4C: vfprintf (in /usr/lib64/libc-2.17.so) ==101781== by 0x56A5C18: printf (in /usr/lib64/libc-2.17.so) ==101781== by 0x400A5C: main (tryvarargs.cpp:68) ==101781== Address 0x5a1304a is 0 bytes after a block of size 10 alloc‘d ==101781== at 0x4C2B974: calloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so) ==101781== by 0x400A1A: main (tryvarargs.cpp:63) ==101781== ==101781== Mismatched free() / delete / delete [] ==101781== at 0x4C2B131: operator delete(void*) (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so) ==101781== by 0x400A68: main (tryvarargs.cpp:69) ==101781== Address 0x5a13040 is 0 bytes inside a block of size 10 alloc‘d ==101781== at 0x4C2B974: calloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so) ==101781== by 0x400A1A: main (tryvarargs.cpp:63) ==101781== abcdefghijk==101781== ==101781== HEAP SUMMARY: ==101781== in use at exit: 0 bytes in 0 blocks ==101781== total heap usage: 1 allocs, 1 frees, 10 bytes allocated ==101781== ==101781== All heap blocks were freed -- no leaks are possible ==101781== ==101781== For counts of detected and suppressed errors, rerun with: -v ==101781== ERROR SUMMARY: 5 errors from 4 contexts (suppressed: 2 from 2)
5、在memcpy和相关函数中重叠src和dst指针
int main(void) { char *buf = (char *)calloc(11, sizeof(char)); for (int i = 0; i < 10; ++i) buf[i] = static_cast<char>(‘a‘ + i); printf("%s", buf); char *dest = buf+3; memcpy(dest, buf, 6); printf("%s", dest); free(buf); }
$ valgrind --tool=memcheck ./heapoverflow ==103964== Memcheck, a memory error detector ==103964== Copyright (C) 2002-2013, and GNU GPL‘d, by Julian Seward et al. ==103964== Using Valgrind-3.10.0 and LibVEX; rerun with -h for copyright info ==103964== Command: ./heapoverflow ==103964== ==103964== Source and destination overlap in memcpy(0x5a13043, 0x5a13040, 6) ==103964== at 0x4C2E1DC: memcpy@@GLIBC_2.14 (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so) ==103964== by 0x400AF0: main (tryvarargs.cpp:72) ==103964== abcdefghijabcdefj==103964== ==103964== HEAP SUMMARY: ==103964== in use at exit: 0 bytes in 0 blocks ==103964== total heap usage: 1 allocs, 1 frees, 11 bytes allocated ==103964== ==103964== All heap blocks were freed -- no leaks are possible ==103964== ==103964== For counts of detected and suppressed errors, rerun with: -v ==103964== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 2 from 2)
参考文献
[1] http://cs.ecs.baylor.edu/~donahoo/tools/valgrind/
[2] http://pages.cs.wisc.edu/~bart/537/valgrind.html
[3] https://www.thegeekstuff.com/2011/11/valgrind-memcheck/
[4] http://valgrind.org/docs/manual/manual.html
标签：heap star eof .com sse parent 很多 tree 运行
原文地址：https://www.cnblogs.com/yshen4/p/9012176.html
