Question

我正在Learn C The Hard Way跟进，我正在Exercise 4: Introducing Valgrind。我在Mac OS X Yosemite上，在撰写本文时，没有稳定的Valgrind for Yosemite版本。我找到了Yosemite and Valgrind并使用了最高投票回答brew install --HEAD valgrind的说明。这个安装了Valgrind和我能够跟随Zed的练习。但是，当我“修复”应用程序时，我仍然遇到错误。

要仔细检查，我回到Exercise 3，这应该没有错误，但我仍然在Valgrind中出错。这是代码，然后是输出：

ex3.c

#include <stdio.h>

int main()
{
    int age = 10;
    int height = 72;

    printf("I am %d years old.\n", age);
    printf("I am %d inches tall.\n", height);

    return 0;
}

在iTerm中：

ransom:learn-c-the-hard-way ben$ rm -f ex3
ransom:learn-c-the-hard-way ben$ make ex3
cc -Wall -g    ex3.c   -o ex3
ransom:learn-c-the-hard-way ben$ valgrind ./ex3
==8795== Memcheck, a memory error detector
==8795== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==8795== Using Valgrind-3.11.0.SVN and LibVEX; rerun with -h for copyright info
==8795== Command: ./ex3
==8795==
==8795== Conditional jump or move depends on uninitialised value(s)
==8795==    at 0x1003FBC3F: _platform_memchr$VARIANT$Haswell (in /usr/lib/system/libsystem_platform.dylib)
==8795==    by 0x1001EFB96: __sfvwrite (in /usr/lib/system/libsystem_c.dylib)
==8795==    by 0x1001F9FE5: __vfprintf (in /usr/lib/system/libsystem_c.dylib)
==8795==    by 0x10021F9AE: __v2printf (in /usr/lib/system/libsystem_c.dylib)
==8795==    by 0x10021FC80: __xvprintf (in /usr/lib/system/libsystem_c.dylib)
==8795==    by 0x1001F5B71: vfprintf_l (in /usr/lib/system/libsystem_c.dylib)
==8795==    by 0x1001F39D7: printf (in /usr/lib/system/libsystem_c.dylib)
==8795==    by 0x100000F2D: main (ex3.c:8)
==8795==
==8795== Conditional jump or move depends on uninitialised value(s)
==8795==    at 0x1003FBC47: _platform_memchr$VARIANT$Haswell (in /usr/lib/system/libsystem_platform.dylib)
==8795==    by 0x1001EFB96: __sfvwrite (in /usr/lib/system/libsystem_c.dylib)
==8795==    by 0x1001F9FE5: __vfprintf (in /usr/lib/system/libsystem_c.dylib)
==8795==    by 0x10021F9AE: __v2printf (in /usr/lib/system/libsystem_c.dylib)
==8795==    by 0x10021FC80: __xvprintf (in /usr/lib/system/libsystem_c.dylib)
==8795==    by 0x1001F5B71: vfprintf_l (in /usr/lib/system/libsystem_c.dylib)
==8795==    by 0x1001F39D7: printf (in /usr/lib/system/libsystem_c.dylib)
==8795==    by 0x100000F2D: main (ex3.c:8)
==8795==
I am 10 years old.
I am 72 inches tall.
==8795==
==8795== HEAP SUMMARY:
==8795==     in use at exit: 38,888 bytes in 426 blocks
==8795==   total heap usage: 506 allocs, 80 frees, 45,016 bytes allocated
==8795==
==8795== LEAK SUMMARY:
==8795==    definitely lost: 0 bytes in 0 blocks
==8795==    indirectly lost: 0 bytes in 0 blocks
==8795==      possibly lost: 0 bytes in 0 blocks
==8795==    still reachable: 4,096 bytes in 1 blocks
==8795==         suppressed: 34,792 bytes in 425 blocks
==8795== Rerun with --leak-check=full to see details of leaked memory
==8795==
==8795== For counts of detected and suppressed errors, rerun with: -v
==8795== Use --track-origins=yes to see where uninitialised values come from
==8795== ERROR SUMMARY: 4 errors from 2 contexts (suppressed: 0 from 0)

它说我Conditional jump or move depends on uninitialized value(s)上的ex3.c:8，但height变量在第6行初始化。

我的猜测是这个问题与Valgrind在Yosemite上出现问题并且错误是假的，但我对C很新，而且我很确定代码是正确的，我也是不知道是否有遗漏的东西。

Valgrind或我的代码有问题吗？

Answer 1

此特定报告对Valgrind来说是误报。 Yosemite上的Valgrind还没有完全覆盖系统库中的所有极端情况以及这些库使用的优化。

此处的提示是函数名称_platform_memchr $ VARIANT $ Haswell，即此错误的存在将取决于您的系统硬件，在这种情况下，您是否拥有基于Intel Haswell的CPU。

如果您可以根据Valgrind的http://valgrind.org/support/bug_reports.html报告此错误，那将是很好的，以便在下一个稳定的Valgrind发布之前修复它。

完全披露：我是Valgrind开发人员之一，他们提供了支持OS X 10.10的补丁

Answer 2

您可以使用参数运行valgrind以忽略库代码。

然后所有那些（你应该忽略的）库错误消息都会消失。

来自valgrind.org 页面：http://valgrind.org/docs/manual/manual-core.html#manual-core.suppress

错误检查工具可检测系统中的许多问题   库，例如C库，它预装了你的   OS。您无法轻松解决这些问题，但您不希望看到这些错误   （是的，有很多！）所以Valgrind读取错误列表   在启动时抑制。默认抑制文件由。创建   系统构建时./configure脚本。

您可以随意修改和添加到抑制文件，或者，   更好，写自己的。允许多个抑制文件。这个   如果您的项目的一部分包含您不能或不能的错误，则非常有用   想要修复，但你不想一直想起它们。

注意：到目前为止，添加抑制的最简单方法是使用   Core Command-line Options中描述的--gen-suppressions=yes选项。这会自动生成抑制。但是，为了获得最佳效果，   您可能想要手动编辑--gen-suppressions=yes的输出   在这种情况下，最好仔细阅读本节。

非常具体地描述要抑制的每个错误   无意中最小化抑制指令的可能性   抑制了一堆你想看到的类似错误。该   抑制机制旨在实现精确而灵活   要压制的错误规范。

Answer 3

Valgrind绝对是优胜美地的实验。但是，我正在以不同的方式（更正确？）运行您的示例。我也使用svn版本，可能比你更新，因为我在测试之前更新了它。另一个区别是我自己建造了它，没有使用brew。

==14456== Memcheck, a memory error detector
==14456== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==14456== Using Valgrind-3.11.0.SVN and LibVEX; rerun with -h for copyright info
==14456== Command: ./t1
==14456==
I am 10 years old.
I am 72 inches tall.
==14456==
==14456== HEAP SUMMARY:
==14456==     in use at exit: 38,396 bytes in 418 blocks
==14456==   total heap usage: 503 allocs, 85 frees, 44,692 bytes allocated
==14456==
==14456== LEAK SUMMARY:
==14456==    definitely lost: 0 bytes in 0 blocks
==14456==    indirectly lost: 0 bytes in 0 blocks
==14456==      possibly lost: 0 bytes in 0 blocks
==14456==    still reachable: 4,096 bytes in 1 blocks
==14456==         suppressed: 34,300 bytes in 417 blocks
==14456== Rerun with --leak-check=full to see details of leaked memory
==14456==
==14456== For counts of detected and suppressed errors, rerun with: -v
==14456== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

<强>更新

这就是我构建valgrind的方法（默认选项）：

./autogen.sh
./configure
make
sudo make install

这是libc（libSystem metalibrary）版本，我的示例二进制文件链接到：

$ otool -L t1
t1:
    /usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1213.0.0)

这是我的铿锵版：

$ clang -v
Apple LLVM version 6.0 (clang-600.0.57) (based on LLVM 3.5svn)
Target: x86_64-apple-darwin14.1.0
Thread model: posix

Answer 4

好吧，我可以添加另一个＆＃34;我在Yosemite＆＃34;上运行我的自制valgrind并不会发生这种情况。该二进制文件的日期为2014-11-25，版本为＆＃34; Valgrind-3.11.0.SVN＆＃34;。运行测试代码，我得到输出：

$ valgrind --suppressions=suppressions ./ex3
==40416== Memcheck, a memory error detector
==40416== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==40416== Using Valgrind-3.11.0.SVN and LibVEX; rerun with -h for copyright info
==40416== Command: ./ex3
==40416== 
--40416-- UNKNOWN mach_msg unhandled MACH_SEND_TRAILER option
--40416-- UNKNOWN mach_msg unhandled MACH_SEND_TRAILER option (repeated 2 times)
--40416-- UNKNOWN mach_msg unhandled MACH_SEND_TRAILER option (repeated 4 times)
I am 10 years old.
I am 72 inches tall.
==40416== 
==40416== HEAP SUMMARY:
==40416==     in use at exit: 39,086 bytes in 428 blocks
==40416==   total heap usage: 511 allocs, 83 frees, 45,358 bytes allocated
==40416== 
==40416== LEAK SUMMARY:
==40416==    definitely lost: 0 bytes in 0 blocks
==40416==    indirectly lost: 0 bytes in 0 blocks
==40416==      possibly lost: 0 bytes in 0 blocks
==40416==    still reachable: 25,940 bytes in 308 blocks
==40416==         suppressed: 13,146 bytes in 120 blocks
==40416== Rerun with --leak-check=full to see details of leaked memory
==40416== 
==40416== For counts of detected and suppressed errors, rerun with: -v
==40416== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
$

我的抑制文件列出了Yosemite运行时的18个泄漏（并且没有访问错误）（如果有帮助，我很乐意分享;它随着时间的推移而被{{1}创建} 选项）。我正在运行一款带有英特尔酷睿i7的老式（2011年初，17英寸）MacBook Pro。

我不喜欢＆＃39; Unknown mach_msg＆＃39;消息，但它们总是出现给我，他们不会明显地停止--gen-suppressions=yes工作（它为我发现了真正的问题，并且没有报告应该工作的代码上的错误）。

我认为你所看到的问题出现在系统库中，并且抑制这两个消息是合理的，但是不得不这样做（很像是不得不抑制这么多的o / s泄漏））。

OS X Yosemite上的Valgrind，出现虚假错误？

4 个答案: