C，叉子上无漏油 [英] C, Leak on fork without malloc

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问题描述

我试图了解内存分配是如何在fork上工作的，甚至在静电或动态分配上也是如此。我很难理解如下所示的一些泄漏。

使用此程序：

#include <unistd.h>
#include <sys/wait.h>

int     main(int argc, char **argv)
{
    pid_t pid;
    int     status;


    pid = fork();
    if (pid == 0)
        return (0);
    else
    {
        waitpid(pid, &status, 0);
        return (0);
    }
}

我正在使用valgrind获取此日志文件：

==81268== Memcheck, a memory error detector
==81268== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==81268== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==81268== Command: ./a.out
==81268== Parent PID: 73556
==81268==
==81268== Syscall param msg->desc.port.name points to uninitialised byte(s)
==81268==    at 0x1003A834A: mach_msg_trap (in /usr/lib/system/libsystem_kernel.dylib)
==81268==    by 0x1003A7796: mach_msg (in /usr/lib/system/libsystem_kernel.dylib)
==81268==    by 0x1003A1485: task_set_special_port (in /usr/lib/system/libsystem_kernel.dylib)
==81268==    by 0x10053D10E: _os_trace_create_debug_control_port (in /usr/lib/system/libsystem_trace.dylib)
==81268==    by 0x10053D458: _libtrace_init (in /usr/lib/system/libsystem_trace.dylib)
==81268==    by 0x1000A69DF: libSystem_initializer (in /usr/lib/libSystem.B.dylib)
==81268==    by 0x100018A1A: ImageLoaderMachO::doModInitFunctions(ImageLoader::LinkContext const&) (in /usr/lib/dyld)
==81268==    by 0x100018C1D: ImageLoaderMachO::doInitialization(ImageLoader::LinkContext const&) (in /usr/lib/dyld)
==81268==    by 0x1000144A9: ImageLoader::recursiveInitialization(ImageLoader::LinkContext const&, unsigned int, char const*, ImageLoader::InitializerTimingList&, ImageLoader::UninitedUpwards&) (in /usr/lib/dyld)
==81268==    by 0x100014440: ImageLoader::recursiveInitialization(ImageLoader::LinkContext const&, unsigned int, char const*, ImageLoader::InitializerTimingList&, ImageLoader::UninitedUpwards&) (in /usr/lib/dyld)
==81268==    by 0x100013523: ImageLoader::processInitializers(ImageLoader::LinkContext const&, unsigned int, ImageLoader::InitializerTimingList&, ImageLoader::UninitedUpwards&) (in /usr/lib/dyld)
==81268==    by 0x1000135B8: ImageLoader::runInitializers(ImageLoader::LinkContext const&, ImageLoader::InitializerTimingList&) (in /usr/lib/dyld)
==81268==  Address 0x10488bc6c is on thread 1's stack
==81268==  in frame #2, created by task_set_special_port (???:)
==81268==
==81269==
==81269== HEAP SUMMARY:
==81269==     in use at exit: 28,557 bytes in 172 blocks
==81269==   total heap usage: 188 allocs, 16 frees, 34,701 bytes allocated
==81269==
==81269== 72 bytes in 3 blocks are possibly lost in loss record 31 of 55
==81269==    at 0x100098BF2: calloc (in /Users/simrossi/.brew/Cellar/valgrind/3.13.0/lib/valgrind/vgpreload_memcheck-amd64-darwin.so)
==81269==    by 0x1005B1846: map_images_nolock (in /usr/lib/libobjc.A.dylib)
==81269==    by 0x1005C4FE8: objc_object::sidetable_retainCount() (in /usr/lib/libobjc.A.dylib)
==81269==    by 0x10000803B: dyld::notifyBatchPartial(dyld_image_states, bool, char const* (*)(dyld_image_states, unsigned int, dyld_image_info const*), bool, bool) (in /usr/lib/dyld)
==81269==    by 0x100008255: dyld::registerObjCNotifiers(void (*)(unsigned int, char const* const*, mach_header const* const*), void (*)(char const*, mach_header const*), void (*)(char const*, mach_header const*)) (in /usr/lib/dyld)
==81269==    by 0x1001FF00A: _dyld_objc_notify_register (in /usr/lib/system/libdyld.dylib)
==81269==    by 0x1005B1074: _objc_init (in /usr/lib/libobjc.A.dylib)
==81269==    by 0x10019268D: _os_object_init (in /usr/lib/system/libdispatch.dylib)
==81269==    by 0x10019263A: libdispatch_init (in /usr/lib/system/libdispatch.dylib)
==81269==    by 0x1000A69D5: libSystem_initializer (in /usr/lib/libSystem.B.dylib)
==81269==    by 0x100018A1A: ImageLoaderMachO::doModInitFunctions(ImageLoader::LinkContext const&) (in /usr/lib/dyld)
==81269==    by 0x100018C1D: ImageLoaderMachO::doInitialization(ImageLoader::LinkContext const&) (in /usr/lib/dyld)
==81269==
==81269== 2,064 (16 direct, 2,048 indirect) bytes in 1 blocks are definitely lost in loss record 51 of 55
==81269==    at 0x100098586: malloc (in /Users/simrossi/.brew/Cellar/valgrind/3.13.0/lib/valgrind/vgpreload_memcheck-amd64-darwin.so)
==81269==    by 0x1004E9103: _nc_table_new (in /usr/lib/system/libsystem_notify.dylib)
==81269==    by 0x1004E4FB5: _notify_init_globals (in /usr/lib/system/libsystem_notify.dylib)
==81269==    by 0x1004F2AC0: _os_once (in /usr/lib/system/libsystem_platform.dylib)
==81269==    by 0x1004F2A91: _os_alloc_once (in /usr/lib/system/libsystem_platform.dylib)
==81269==    by 0x1004E50AD: _notify_fork_child (in /usr/lib/system/libsystem_notify.dylib)
==81269==    by 0x1000A6B20: libSystem_atfork_child (in /usr/lib/libSystem.B.dylib)
==81269==    by 0x10026F436: fork (in /usr/lib/system/libsystem_c.dylib)
==81269==    by 0x100000F4A: main (in ./a.out)
==81269==
==81269== 2,064 (16 direct, 2,048 indirect) bytes in 1 blocks are definitely lost in loss record 52 of 55
==81269==    at 0x100098586: malloc (in /Users/simrossi/.brew/Cellar/valgrind/3.13.0/lib/valgrind/vgpreload_memcheck-amd64-darwin.so)
==81269==    by 0x1004E9103: _nc_table_new (in /usr/lib/system/libsystem_notify.dylib)
==81269==    by 0x1004E4FC6: _notify_init_globals (in /usr/lib/system/libsystem_notify.dylib)
==81269==    by 0x1004F2AC0: _os_once (in /usr/lib/system/libsystem_platform.dylib)
==81269==    by 0x1004F2A91: _os_alloc_once (in /usr/lib/system/libsystem_platform.dylib)
==81269==    by 0x1004E50AD: _notify_fork_child (in /usr/lib/system/libsystem_notify.dylib)
==81269==    by 0x1000A6B20: libSystem_atfork_child (in /usr/lib/libSystem.B.dylib)
==81269==    by 0x10026F436: fork (in /usr/lib/system/libsystem_c.dylib)
==81269==    by 0x100000F4A: main (in ./a.out)
==81269==
==81269== LEAK SUMMARY:
==81269==    definitely lost: 32 bytes in 2 blocks
==81269==    indirectly lost: 4,096 bytes in 2 blocks
==81269==      possibly lost: 72 bytes in 3 blocks
==81269==    still reachable: 200 bytes in 6 blocks
==81269==         suppressed: 24,157 bytes in 159 blocks
==81269== Reachable blocks (those to which a pointer was found) are not shown.
==81269== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==81269==
==81269== For counts of detected and suppressed errors, rerun with: -v
==81269== Use --track-origins=yes to see where uninitialised values come from
==81269== ERROR SUMMARY: 5 errors from 4 contexts (suppressed: 13 from 13)
==81268==
==81268== HEAP SUMMARY:
==81268==     in use at exit: 18,127 bytes in 159 blocks
==81268==   total heap usage: 175 allocs, 16 frees, 24,271 bytes allocated
==81268==
==81268== 72 bytes in 3 blocks are possibly lost in loss record 26 of 42
==81268==    at 0x100098BF2: calloc (in /Users/simrossi/.brew/Cellar/valgrind/3.13.0/lib/valgrind/vgpreload_memcheck-amd64-darwin.so)
==81268==    by 0x1005B1846: map_images_nolock (in /usr/lib/libobjc.A.dylib)
==81268==    by 0x1005C4FE8: objc_object::sidetable_retainCount() (in /usr/lib/libobjc.A.dylib)
==81268==    by 0x10000803B: dyld::notifyBatchPartial(dyld_image_states, bool, char const* (*)(dyld_image_states, unsigned int, dyld_image_info const*), bool, bool) (in /usr/lib/dyld)
==81268==    by 0x100008255: dyld::registerObjCNotifiers(void (*)(unsigned int, char const* const*, mach_header const* const*), void (*)(char const*, mach_header const*), void (*)(char const*, mach_header const*)) (in /usr/lib/dyld)
==81268==    by 0x1001FF00A: _dyld_objc_notify_register (in /usr/lib/system/libdyld.dylib)
==81268==    by 0x1005B1074: _objc_init (in /usr/lib/libobjc.A.dylib)
==81268==    by 0x10019268D: _os_object_init (in /usr/lib/system/libdispatch.dylib)
==81268==    by 0x10019263A: libdispatch_init (in /usr/lib/system/libdispatch.dylib)
==81268==    by 0x1000A69D5: libSystem_initializer (in /usr/lib/libSystem.B.dylib)
==81268==    by 0x100018A1A: ImageLoaderMachO::doModInitFunctions(ImageLoader::LinkContext const&) (in /usr/lib/dyld)
==81268==    by 0x100018C1D: ImageLoaderMachO::doInitialization(ImageLoader::LinkContext const&) (in /usr/lib/dyld)
==81268==
==81268== LEAK SUMMARY:
==81268==    definitely lost: 0 bytes in 0 blocks
==81268==    indirectly lost: 0 bytes in 0 blocks
==81268==      possibly lost: 72 bytes in 3 blocks
==81268==    still reachable: 200 bytes in 6 blocks
==81268==         suppressed: 17,855 bytes in 150 blocks
==81268== Reachable blocks (those to which a pointer was found) are not shown.
==81268== To see them, rerun with: --leak-check=full --show-leak-kinds=all
==81268==
==81268== For counts of detected and suppressed errors, rerun with: -v
==81268== Use --track-origins=yes to see where uninitialised values come from
==81268== ERROR SUMMARY: 2 errors from 2 contexts (suppressed: 12 from 12)
我不知道那32个字节和4096个字节的泄漏是从哪里来的？它来自标准库吗，我在Stackoverflow上看到过类似的东西。我使用的是Mac OS Sierra x86_64。

编辑：如果我不派生，我不会得到任何泄漏，这似乎与函数调用有关。

推荐答案

MacOS上程序的启动代码分配了大量从未释放的内存。对于正在分配的内存，您无能为力。然而，你可以告诉Valgrind关于泄密的事情，并说服它忽略它们。我认为fork()是无关紧要的-即使没有它，你也可能会看到泄漏。

您需要使用选项运行这样的程序以生成取消显示，在文件中捕获取消显示，然后(将来)指定您创建的取消显示文件运行。

您可以在Valgrind shows memory leak with empty main without including headers查看工作示例。

这篇关于C，叉子上无漏油的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！

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