xcode 来自链接器的奇怪警告 (ld)

Strange warnings from the linker (ld)

提问by ItalyPaleAle

We are building a Mac OSX application which is written mostly in Obj-C/Cocoa. The application then statically links with some 3rd party libraries, written in C/C++ and compiled by us (on a command line, using either MacPorts or the usual "./configure && make"; all are universal binaries).

我们正在构建一个主要用 Obj-C/Cocoa 编写的 Mac OSX 应用程序。然后，该应用程序与一些用 C/C++ 编写并由我们编译的 3rd 方库静态链接（在命令行上，使用 MacPorts 或通常的“./configure && make”；所有都是通用二进制文件）。

The application is working perfectly, but ad compile time we are always getting these strange linker warnings:

该应用程序运行良好，但广告编译时我们总是收到这些奇怪的链接器警告：

ld: warning: direct access in ___cxx_global_var_init17 to global weak symbol __ZGVN4i18n12phonenumbers9SingletonINS0_15PhoneNumberUtilEE8instanceE means the weak symbol cannot be overridden at runtime. This was likely caused by different translation units being compiled with different visibility settings.
ld: warning: direct access in ___cxx_global_var_init17 to global weak symbol __ZGVN4i18n12phonenumbers9SingletonINS0_15PhoneNumberUtilEE8instanceE means the weak symbol cannot be overridden at runtime. This was likely caused by different translation units being compiled with different visibility settings.
ld: warning: direct access in ___cxx_global_var_init17 to global weak symbol __ZN5boost10scoped_ptrIN4i18n12phonenumbers15PhoneNumberUtilEED1Ev means the weak symbol cannot be overridden at runtime. This was likely caused by different translation units being compiled with different visibility settings.
ld: warning: direct access in ___cxx_global_var_init17 to global weak symbol __ZN4i18n12phonenumbers9SingletonINS0_15PhoneNumberUtilEE8instanceE means the weak symbol cannot be overridden at runtime. This was likely caused by different translation units being compiled with different visibility settings.
ld: warning: direct access in ___cxx_global_var_init17 to global weak symbol __ZGVN4i18n12phonenumbers9SingletonINS0_15PhoneNumberUtilEE8instanceE means the weak symbol cannot be overridden at runtime. This was likely caused by different translation units being compiled with different visibility settings.

This comes from a C/C++ library. We are linking with these libs:

这来自 C/C++ 库。我们正在与这些库链接：

1. libphonenumber, which is the one causing 4 of the 5 warnings, apparently. Compiled by us via "cmake".
2. boost (libboost_thread-mt), responsible of 1 warning. Compiled with MacPorts.
3. ICU (libicudata, libicuuc, libicui18n), compiled with MacPorts.
4. Protocol Buffers, compiled via "./configure && make".

1. libphonenumber，显然是导致 5 个警告中的 4 个的那个。我们通过“cmake”编译。
2. boost (libboost_thread-mt)，负责 1 个警告。用 MacPorts 编译。
3. ICU (libicudata, libicuuc, libicui18n)，用 MacPorts 编译。
4. Protocol Buffers，通过“./configure && make”编译。

Please note:

请注意：

1. The application is working perfectly despite the warnings, but we'd like to get rid of them as they are annoying.
2. The solution proposed by xcode with boost : linker(Id) Warning about visibility settingsdoesn't work: "Symbols hidden by default" has always been "YES".

1. 尽管有警告，该应用程序运行良好，但我们希望摆脱它们，因为它们很烦人。
2. xcode提出的带有 boost的解决方案：linker(Id) 关于可见性设置的警告不起作用：“默认隐藏的符号”始终为“是”。

采纳答案by inspector-g

The solution proposed by xcode with boost : linker(Id) Warning about visibility settings doesn't work: "Symbols hidden by default" has always been "YES".

xcode 提出的带有 boost 的解决方案：linker(Id) 关于可见性设置的警告不起作用：“默认隐藏的符号”始终为“是”。

This has less to do with being set to "YES", and more to do with being set to the same value across all projects. Libs/projects that depend on other libs need to have a likewise setting for "Symbols hidden by default" in order to link properly and free of errors/warnings.

这与设置为“YES”的关系不大，而与在所有项目中设置为相同的值有关。依赖于其他库的库/项目需要对“默认隐藏的符号”进行类似的设置，以便正确链接并且没有错误/警告。

I've run into this before, and a simple change in Xcode for all projects to ensure the settings match typically resolves the problem. Since it sounds like you're compiling on the command line as well, the -fvisibilityargument to gccis what you need to look at.

我以前遇到过这种情况，并且对所有项目在 Xcode 中进行简单更改以确保设置匹配通常可以解决问题。由于听起来您也在命令行上进行编译，因此您需要查看-fvisibility参数 to gcc。

回答by johnwbyrd

tl:dr; use -fvisibility=hiddenas a gcc and llvm compiler switch in everything you compile, includingyour dependent libraries, unless you have a reason not to.

tl：博士；用-fvisibility=hidden在一切编译，一个GCC和LLVM编译器开关，包括你的依赖库，除非你有充分的理由不这样做。

A good introduction to the -fvisibility and -fvisibility-inline-hidden compilation flags is available on Apple's web site, as of this writing. The article also goes into some detail on the __attribute__((visibility("hidden")))and __attribute__((visibility("default")))declarations.

在撰写本文时，Apple 网站上提供了对 -fvisibility 和 -fvisibility-inline-hidden 编译标志的很好的介绍。本文还详细介绍了__attribute__((visibility("hidden")))和__attribute__((visibility("default")))声明。

回答by guest2016

I got the warning gone in Xcode by putting -fvisibility=hidden -fvisibility-inlines-hiddeninto OTHER C++ FLAGS.

通过放入-fvisibility=hidden -fvisibility-inlines-hiddenOTHER C++ FLAGS，我在 Xcode 中得到了警告。

回答by Nick

I also got this, for similar reasons, but I think the problem was inconsistency of the inlining visibility settings.

由于类似的原因，我也得到了这个，但我认为问题在于内联可见性设置的不一致。

See http://lists.cs.uiuc.edu/pipermail/llvmdev/2011-December/046505.html

见http://lists.cs.uiuc.edu/pipermail/llvmdev/2011-December/046505.html

I set all inlining hidden to no and the warning (finally) went away.

我将所有内联设置为 no，警告（终于）消失了。