Valgrind报告一个非常简单的C程序的错误

Question

我正在通过“学习C 艰辛的方式”学习C语言。 我正在练习6 ，虽然我可以使它起作用，但是valgrind报告很多错误。

这是ex6.c文件中ex6.c最小程序：

#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;
}

Makefile内容只是CFLAGS=-Wall -g 。

我用$ make ex6编译程序（没有编译器警告或错误）。 用$ ./ex6执行会产生预期的输出。

当我使用$ valgrind ./ex6运行程序时，出现无法解决的错误。 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)

我正在使用OS X优胜美地。 Valgrind是通过安装brew用这个命令$ brew install valgrind --HEAD 。

那么，有人知道这是什么问题吗？ 如何解决valgrind错误？

Answer 1

如果您通过Valgrind运行的程序恰好是您在问题中发布的程序，则显然没有任何内存泄漏。 实际上，您自己甚至都不使用malloc / free！

在我看来，这些都是Valgrind在OS X上（仅！）检测到的虚假错误/误报，类似于一段时间前发生在我身上的情况 。

如果您可以访问其他操作系统，例如Linux机器，请尝试在该系统上使用Valgrind分析程序。

编辑：我自己还没有尝试过此操作，因为我现在无法访问Mac，但是您应该尝试M Oehm的建议： 尝试使用另一个SO问题中提到的 supressions 文件 。

Answer 2

对于使用Valgrind r14960 with VEX r3124 r3124和Xcode 6.3的Valgrind r15088 Darwin 14.3.0（Mac OS X 10.10.2），此问题已修复。

如果您正在使用Macports（在撰写本文时），那么sudo port install valgrind-devel将为您Valgrind r14960 with VEX r3093 。

这是我Valgrind r14960 with VEX r3124安装Valgrind r14960 with VEX r3124构建脚本：

#! /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安装的valgrind位于/opt/local/bin/valgrind 。

如果我现在跑步

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

我将得到与上述完全相同的错误。 （在这里使用我的objc.supp文件https://gist.github.com/calvinchengx/0b1d45f67be9fdca205b ）

但是如果我跑步

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

一切都按预期工作，并且我没有出现系统级内存泄漏错误。

Answer 3

从该主题来看，我认为不能保证valgrind在您的平台上给出正确的结果。 如果可以，请在其他平台上尝试此代码。

罪魁祸首要么在valgrid本身，要么在系统的printf实现中，而这两者对于您都无法修复。

Rerun with --leak-check=full to see details of leaked memory. 这应该为您提供有关所遇到的泄漏的更多信息。 如果没有帮助，则可以创建一个抑制文件以阻止显示错误。