无法重现项目示例项目的内存清除结果

Question

我从centos7中获得了完全相同的结果，clang-3.6.1是使用fedora文件从源代码构建的。Ubuntu 14.04，clang-3.4

尽可能地使用来自wiki的说明，https://github.com/google/sanitizers/wiki/MemorySanitizerLibcxxHowTo。这一页是6个月前更新的。

谷歌613仍在使用tr1

In file included from /home/hal/googletest/src/gtest-all.cc:39:
In file included from /home/hal/googletest/include/gtest/gtest.h:58:
In file included from /home/hal/googletest/include/gtest/internal/gtest-internal.h:40:
/home/hal/googletest/include/gtest/internal/gtest-port.h:507:13: fatal error: 
      'tr1/tuple' file not found
#   include <tr1/tuple>  // NOLINT
            ^
1 error generated.

将googletest更新为提示(746)，并使用以下警告进行编译

➜ [hal@davis 9:54 ~/gtest-msan] make
Scanning dependencies of target gtest
[ 50%] Building CXX object CMakeFiles/gtest.dir/src/gtest-all.cc.o
clang: warning: -lc++abi: 'linker' input unused
clang: warning: -lc++abi: 'linker' input unused
clang: warning: argument unused during compilation: '-L/home/hal/libcxx_msan/lib'
clang: warning: argument unused during compilation: '-L/home/hal/libcxx_msan/lib'
Linking CXX static library libgtest.a

从那一页上提到的琐碎的案子没有被msan拿出来

[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from FooTest
[ RUN      ] FooTest.Foo
test.cc:7: Failure
Value of: foo[4]
  Actual: '\0'
Expected: 'z'
Which is: 'z' (122, 0x7A)
[  FAILED  ] FooTest.Foo (1 ms)
[----------] 1 test from FooTest (1 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (1 ms total)
[  PASSED  ] 0 tests.
[  FAILED  ] 1 test, listed below:
[  FAILED  ] FooTest.Foo

 1 FAILED TEST

我有一个项目，由于使用了一些非常大的mmap，所以使用valgrind，所以内存清理将非常有用。如果我做错了什么。似乎googletest在某种程度上抑制了错误。移除google测试并将测试用例转换为

如果(foo4 == 'z') std::cout <<“是z”<< std::endl；

按预期触发明显错误的报告。

==29128== WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x7f59270c1738 in std::string::_Rep::_M_is_leaked() const /usr/lib/gcc/x86_64-redhat-linux/4.8.5/../../../../include/c++/4.8.5/bits/basic_string.h:192:18
    #1 0x7f59270c1738 in std::string::_M_leak() /usr/lib/gcc/x86_64-redhat-linux/4.8.5/../../../../include/c++/4.8.5/bits/basic_string.h:316
    #2 0x7f59270c1738 in std::string::operator[](unsigned long) /usr/lib/gcc/x86_64-redhat-linux/4.8.5/../../../../include/c++/4.8.5/bits/basic_string.h:849
    #3 0x7f59270c1738 in main /home/hal/test-gtest-msan/test2.cc:7
    #4 0x7f5925c2bb14 in __libc_start_main (/lib64/libc.so.6+0x21b14)
    #5 0x7f592706ce30 in _start (/home/hal/test-gtest-msan/test2+0x35e30)

  Uninitialized value was created by an allocation of 'foo' in the stack frame of function 'main'
    #0 0x7f59270c12e0 in main /home/hal/test-gtest-msan/test2.cc:4

SUMMARY: MemorySanitizer: use-of-uninitialized-value /usr/lib/gcc/x86_64-redhat-linux/4.8.5/../../../../include/c++/4.8.5/bits/basic_string.h:192 std::string::_Rep::_M_is_leaked() const
Exiting

是否可以通过单元测试库使用内存清理？

Answer 1

这不是MemorySanitizer或googletest问题:很明显，libc++最近发生了变化，现在它在实际的四字节字符串"foo“之外初始化字节，因此MSan没有为这种非绑定访问生成报告。

对MSan wiki进行了更新，以使用另一个示例，对此错误按预期的方式报告：

TEST(FooTest, Foo) {
  int uninitialized;
  EXPECT_GT(uninitialized, 5);
}

在以下方面的成果：

[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from FooTest
[ RUN      ] FooTest.Foo
==39032== WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x48d73c in testing::AssertionResult testing::internal::CmpHelperGT<int, int>(char const*, char const*, int const&, int const&) googletest/include/gtest/gtest.h:1463:1
    #1 0x48ce7a in FooTest_Foo_Test::TestBody() test.cc:6:3
...

在配置googletest以在第613版构建-DGTEST_USE_OWN_TR1_TUPLE=1时，可以添加编译标志。

Answer 2

因为在单元测试中看到的值是'\0'，所以可能是字符串实际上初始化了位置4的内存，以便与C-字符串兼容(尾随为零)。单元测试和手动测试用例之间的差异可能是编译器优化的结果。如果将字符串切换到std::vector<char>{'f', 'o', 'o'}会发生什么？

如果您也可以发布单元测试代码，这将是有帮助的。