为什么valgrind报告我的记忆为“绝对丢失"? [英] Why valgrind report my memory as "definitely lost"?
问题描述
考虑以下代码:
#include <stdlib.h>
int* alloc()
{
return malloc(250 * sizeof(int));
}
int main()
{
int i;
int *vars[3];
for(i = 0; i < 3; ++i) {
vars[i] = alloc();
}
}
Valgrind输出:
Valgrind output:
$ valgrind --leak-check=full ./lala
==16775== Memcheck, a memory error detector
==16775== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==16775== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==16775== Command: ./lala
==16775==
==16775==
==16775== HEAP SUMMARY:
==16775== in use at exit: 3,000 bytes in 3 blocks
==16775== total heap usage: 3 allocs, 0 frees, 3,000 bytes allocated
==16775==
==16775== 3,000 bytes in 3 blocks are definitely lost in loss record 1 of 1
==16775== at 0x4C2BBA0: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==16775== by 0x4005B3: alloc (lala.c:5)
==16775== by 0x4005DF: main (lala.c:13)
==16775==
==16775== LEAK SUMMARY:
==16775== definitely lost: 3,000 bytes in 3 blocks
==16775== indirectly lost: 0 bytes in 0 blocks
==16775== possibly lost: 0 bytes in 0 blocks
==16775== still reachable: 0 bytes in 0 blocks
==16775== suppressed: 0 bytes in 0 blocks
==16775==
==16775== For counts of detected and suppressed errors, rerun with: -v
==16775== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)
根据 Valgrind的手册:>
如果--leak-check设置正确,则对于其余每个块, Memcheck确定是否可以通过指针中的指针访问该块 根集.根集由(a)的通用寄存器组成 所有线程,以及(b)初始化,对齐,指针大小的数据字 可访问的客户端内存,包括堆栈.
If --leak-check is set appropriately, for each remaining block, Memcheck determines if the block is reachable from pointers within the root-set. The root-set consists of (a) general purpose registers of all threads, and (b) initialized, aligned, pointer-sized data words in accessible client memory, including stacks.
据我了解,由于仍然从main()
函数的堆栈中指向绝对丢失"的内存,因此应该将它们归类为仍可访问",对吗?
For what I understand, since the "definitely lost" memory are still pointed to from the main()
function's stack, they should be categorized as "still reachable", right?
如果没有,我如何配置Valgrind尝试从main
的堆栈访问内存块,以确定它们是否仍可访问"?
If not, how can I configure Valgrind to try to reach memory blocks from main
's stack, to determine if they are "still reachable"?
请不要告诉我free
在main
末尾的指针,这不是我要问的.对于Valgrind术语上的仍然可以到达"和绝对丢失"之间的区别,请参见以下答案: https://stackoverflow.com/a /3857638/578749
Please don't tell me to free
the pointers at the end of main
, that is not what I am asking about. For the distinction between "still reachable" and "definitely lost" on Valgrind terms, see this answer: https://stackoverflow.com/a/3857638/578749
推荐答案
当main
的堆栈被破坏(即返回)时,您的内存肯定会丢失.因此,解决方案是不返回.
Your memory is definitely lost when the stack of main
is destroyed, that is, when it returns. Thus, the solution is not to return.
#include <stdlib.h>
int main()
{
/* your code here */
exit(0);
}
返回0或exit(0)
的行为或主函数应等效.
The behavior or main returning 0 or exit(0)
should be equivalent.
现在的输出是:
==5035== Memcheck, a memory error detector
==5035== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==5035== Using Valgrind-3.10.1 and LibVEX; rerun with -h for copyright info
==5035== Command: ./a.out
==5035==
==5035==
==5035== HEAP SUMMARY:
==5035== in use at exit: 3,000 bytes in 3 blocks
==5035== total heap usage: 3 allocs, 0 frees, 3,000 bytes allocated
==5035==
==5035== LEAK SUMMARY:
==5035== definitely lost: 0 bytes in 0 blocks
==5035== indirectly lost: 0 bytes in 0 blocks
==5035== possibly lost: 0 bytes in 0 blocks
==5035== still reachable: 3,000 bytes in 3 blocks
==5035== suppressed: 0 bytes in 0 blocks
==5035== Reachable blocks (those to which a pointer was found) are not shown.
==5035== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==5035==
==5035== For counts of detected and suppressed errors, rerun with: -v
==5035== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
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