c - 退出时释放 LLVM 分配的所有内存

Question

我正在使用 LLVM-C 编写一种小玩具语言。我还使用 valgrind 来检查内存泄漏。

这是我的基本婴儿程序:

#include <stdio.h>
#include <llvm-c/Core.h>

int main()
{
    size_t length;
    LLVMModuleRef module = LLVMModuleCreateWithName("llvm.hello");
    printf("Module name: %s\n", LLVMGetModuleIdentifier(module, &length));
    LLVMDisposeModule(module);
    LLVMShutDown();
    return 0;
}

我可以像预期的那样正常编译和运行程序。然而，当我通过 valgrind 运行程序时，它告诉我我有一些像这样的“仍然可以访问”的分配内存。

valgrind  --leak-check=full  out/hello_llvm

==5807== LEAK SUMMARY:
==5807==    definitely lost: 0 bytes in 0 blocks
==5807==    indirectly lost: 0 bytes in 0 blocks
==5807==      possibly lost: 0 bytes in 0 blocks
==5807==    still reachable: 56 bytes in 2 blocks
==5807==         suppressed: 0 bytes in 0 blocks

在这个站点上搜索答案时，我发现许多编码人员都说“仍然可以访问”内存泄漏并不是什么大问题。我不想争论这个。我想要的是在终止我的程序之前摆脱所有分配的内存。

有什么方法可以在终止前将分配的内存减少到零？

Answer 1

当 valgrind 不给出 0 时，这也让我非常紧张，在这种情况下我创建了一个抑制文件，如果你想试一试:

创建并编译一个最小测试:

> cat demo.c
#include <stdlib.h>

int main(void)
{
    malloc(10); // leak
}

创建抑制文件:

valgrind --leak-check=full --show-reachable=yes --error-limit=no --gen-suppressions=all --log-file=minimal.supp ./demo

编辑生成的minimal.supp文件，你会看到类似的东西

==3102== Memcheck, a memory error detector
==3102== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==3102== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==3102== Command: ./demo
==3102== Parent PID: 2633
==3102== 
==3102== 
==3102== HEAP SUMMARY:
==3102==     in use at exit: 10 bytes in 1 blocks
==3102==   total heap usage: 1 allocs, 0 frees, 10 bytes allocated
==3102== 
==3102== 10 bytes in 1 blocks are definitely lost in loss record 1 of 1
==3102==    at 0x483B7F3: malloc (in /usr/lib/x86_64-linux-gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==3102==    by 0x10915A: main (in /home/david/demo)
==3102== 
{
   <insert_a_suppression_name_here>
   Memcheck:Leak
   match-leak-kinds: definite
   fun:malloc
   fun:main
}
==3102== LEAK SUMMARY:
==3102==    definitely lost: 10 bytes in 1 blocks
==3102==    indirectly lost: 0 bytes in 0 blocks
==3102==      possibly lost: 0 bytes in 0 blocks
==3102==    still reachable: 0 bytes in 0 blocks
==3102==         suppressed: 0 bytes in 0 blocks
==3102== 
==3102== For lists of detected and suppressed errors, rerun with: -s
==3102== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)

删除所有以 == 开头的行并保存如下内容:

{
   <my stupid external LLVM leak>
   Memcheck:Leak
   match-leak-kinds: definite
   fun:malloc
   fun:main
}

现在使用抑制文件运行 valgrind:

valgrind --tool=memcheck --leak-check=full --show-reachable=yes --error-limit=no --suppressions=minimal.supp ./demo

结果是:

==3348== Memcheck, a memory error detector
==3348== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==3348== Using Valgrind-3.15.0 and LibVEX; rerun with -h for copyright info
==3348== Command: ./demo
==3348== 
==3348== 
==3348== HEAP SUMMARY:
==3348==     in use at exit: 10 bytes in 1 blocks
==3348==   total heap usage: 1 allocs, 0 frees, 10 bytes allocated
==3348== 
==3348== LEAK SUMMARY:
==3348==    definitely lost: 0 bytes in 0 blocks
==3348==    indirectly lost: 0 bytes in 0 blocks
==3348==      possibly lost: 0 bytes in 0 blocks
==3348==    still reachable: 0 bytes in 0 blocks
==3348==         suppressed: 10 bytes in 1 blocks
==3348== 
==3348== For lists of detected and suppressed errors, rerun with: -s
==3348== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 1 from 1)

如您所见，泄漏已从“绝对丢失”移至“抑制”