Valgrind报告了一个非常简单的C程序的错误

Question

我正在从Learn C The Hard Way学习C语言.我正在练习6,虽然我可以使它工作,但valgrind会报告很多错误.

这是从文件中删除的最小程序ex6.c:

#include <stdio.h>

int main(int argc, char *argv[])
{
    char initial = 'A';
    float power = 2.345f;

    printf("Character is %c.\n", initial);
    printf("You have %f levels of power.\n", power);

    return 0;
}

内容Makefile只是CFLAGS=-Wall -g.

我编译程序$ make ex6(没有编译器警告或错误).执行with $ ./ex6产生预期的输出.

当我运行程序时,$ valgrind ./ex6我得到了我无法解决的错误.这是完整的输出:

==69691== Memcheck, a memory error detector
==69691== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==69691== Using Valgrind-3.11.0.SVN and LibVEX; rerun with -h for copyright info
==69691== Command: ./ex6
==69691==
--69691-- UNKNOWN mach_msg unhandled MACH_SEND_TRAILER option
--69691-- UNKNOWN mach_msg unhandled MACH_SEND_TRAILER option (repeated 2 times)
--69691-- UNKNOWN mach_msg unhandled MACH_SEND_TRAILER option (repeated 4 times)
==69691== Conditional jump or move depends on uninitialised value(s)
==69691==    at 0x1003FBC3F: _platform_memchr$VARIANT$Haswell (in /usr/lib/system/libsystem_platform.dylib)
==69691==    by 0x1001EFBB6: __sfvwrite (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x1001FA005: __vfprintf (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x10021F9CE: __v2printf (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x10021FCA0: __xvprintf (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x1001F5B91: vfprintf_l (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x1001F39F7: printf (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x100000F1B: main (ex6.c:8)
==69691==
Character is A.
==69691== Invalid read of size 32
==69691==    at 0x1003FBC1D: _platform_memchr$VARIANT$Haswell (in /usr/lib/system/libsystem_platform.dylib)
==69691==    by 0x1001EFBB6: __sfvwrite (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x1001FA005: __vfprintf (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x10021F9CE: __v2printf (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x10021FCA0: __xvprintf (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x1001F5B91: vfprintf_l (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x1001F39F7: printf (in /usr/lib/system/libsystem_c.dylib)
==69691==    by 0x100000F31: main (ex6.c:9)
==69691==  Address 0x100809680 is 32 bytes before a block of size 32 in arena "client"
==69691==
You have 2.345000 levels of power.
==69691==
==69691== HEAP SUMMARY:
==69691==     in use at exit: 39,365 bytes in 429 blocks
==69691==   total heap usage: 510 allocs, 81 frees, 45,509 bytes allocated
==69691==
==69691== LEAK SUMMARY:
==69691==    definitely lost: 16 bytes in 1 blocks
==69691==    indirectly lost: 0 bytes in 0 blocks
==69691==      possibly lost: 13,090 bytes in 117 blocks
==69691==    still reachable: 26,259 bytes in 311 blocks
==69691==         suppressed: 0 bytes in 0 blocks
==69691== Rerun with --leak-check=full to see details of leaked memory
==69691==
==69691== For counts of detected and suppressed errors, rerun with: -v
==69691== Use --track-origins=yes to see where uninitialised values come from
==69691== ERROR SUMMARY: 5 errors from 2 contexts (suppressed: 0 from 0)

我在OS X yosemite.brew使用此命令安装Valgrind $ brew install valgrind --HEAD.

那么,有谁知道这里的问题是什么？如何修复valgrind错误？

Answer 1

如果您通过Valgrind运行的程序正是您在问题中发布的程序,那么它显然没有任何内存泄漏.事实上,你甚至不用自己的malloc/free!

在我看来,这些是Valgrind在OS X上检测到的虚假错误/误报(仅限!),类似于我前一段时间发生的事情.

如果您可以访问其他操作系统,例如Linux机器,请尝试使用该系统上的Valgrind分析程序.

编辑:我自己没有尝试过,因为我现在无法访问Mac,但你应该尝试M Oehm建议的内容:尝试使用其他SO问题中提到的 supressions 文件.

Answer 2

对于使用Valgrind r14960 with VEX r3124Xcode6.2和Valgrind r15088Xcode 6.3的Darwin 14.3.0(Mac OS X 10.10.2),此问题已得到修复.

如果您正在使用Macports(在撰写本文时),sudo port install valgrind-devel将会给您Valgrind r14960 with VEX r3093.

这是我要安装的构建脚本Valgrind r14960 with VEX r3124:

#! /usr/bin/env bash

mkdir -p buildvalgrind
cd buildvalgrind
svn co svn://svn.valgrind.org/valgrind/trunk/@14960 valgrind
cd valgrind
./autogen.sh
./configure --prefix=/usr/local
make && sudo make install

# check that we have our valgrind installed
/usr/local/bin/valgrind --version 

(参考:http://calvinx.com/2015/04/10/valgrind-on-mac-os-x-10-10-yosemite/)

我的macports-installed valgrind位于/opt/local/bin/valgrind.

如果我现在跑

/opt/local/bin/valgrind --leak-check=yes --suppressions=`pwd`/objc.supp ./ex6

我将得到与您上面描述的完全相同的错误.(objc.supp在这里使用我的文件https://gist.github.com/calvinchengx/0b1d45f67be9fdca205b)

但是,如果我跑

/usr/local/bin/valgrind --leak-check=yes --suppressions=`pwd`/objc.supp ./ex6

一切都按预期工作,我没有出现系统级内存泄漏错误.