GCC:用于静态链接到pthread的--whole-archive配方在最新的gcc版本中停止工作 [英] GCC: --whole-archive recipe for static linking to pthread stopped working in recent gcc versions

查看：301 发布时间：2020/11/12 22:51:37 c++ gcc pthreads static-linking

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问题描述

在Linux上，针对pthread的静态链接是一个困难的话题.

Static linking against pthread is a difficult topic on Linux. It used to work to wrap -lpthread as -Wl,--whole-archive -lpthread -Wl,--no-whole-archive (the details can be found in this answer).

结果是(用于pthread的)符号强但不弱.自从Ubuntu 18.04左右(在gcc 5.4.0和gcc 7.4.0之间)以来，这种行为似乎已经改变，pthread符号现在始终以弱符号结尾，而与--whole-archive选项无关.

The effect was that symbols (for pthread) were strong, not weak. Since around Ubuntu 18.04 (between gcc 5.4.0 and gcc 7.4.0) that behavior seemed to have changed, and pthread symbols now always end up as weak symbols independent of the --whole-archive option.

因此，-whole-archive配方停止工作.我的问题的目的是了解工具链中最近发生了哪些变化(编译器，链接器，标准库)，以及可以采取哪些措施来恢复旧的行为.

Because of that, the -whole-archive recipe stopped working. The intention of my question is to understand what has changed recently in the toolchain (compiler, linker, standard libray), and what can be done to get the old behavior back.

示例:

#include <mutex>

int main(int argc, char **argv) {
  std::mutex mutex;
  mutex.lock();
  mutex.unlock();
  return 0;
}

在以下所有示例中，都使用了相同的编译命令:

In all following examples, the same compilation command was used:

g++ -std=c++11 -Wall -static simple.cpp  -Wl,--whole-archive -lpthread  -Wl,--no-whole-archive

之前，使用-static进行编译时，pthread符号(例如，pthread_mutex_lock)很强(由T "rel =" nofollow noreferrer> nm )，但现在它们很弱(W):

Before, when compiling with -static, pthread symbols (e.g., pthread_mutex_lock) were strong (marked as T by nm), but now they are weak (W):

Ubuntu 14.04:docker run --rm -it ubuntu:14.04 bash

Ubuntu 14.04: docker run --rm -it ubuntu:14.04 bash

$ apt-get update
$ apt-get install g++

$ g++ --version
g++ (Ubuntu 4.8.4-2ubuntu1~14.04.4) 4.8.4

$ nm a.out | grep pthread_mutex_lock
0000000000408160 T __pthread_mutex_lock
00000000004003e0 t __pthread_mutex_lock_full
0000000000408160 T pthread_mutex_lock

Ubuntu 16.04:docker run --rm -it ubuntu:16.04 bash

Ubuntu 16.04: docker run --rm -it ubuntu:16.04 bash

$ g++ --version
g++ (Ubuntu 5.4.0-6ubuntu1~16.04.12) 5.4.0 20160609

$ nm a.out | grep pthread_mutex_lock
00000000004077b0 T __pthread_mutex_lock
0000000000407170 t __pthread_mutex_lock_full
00000000004077b0 T pthread_mutex_lock

Ubuntu 18.04:docker run --rm -it ubuntu:18.04 bash

Ubuntu 18.04: docker run --rm -it ubuntu:18.04 bash

$ g++ --version
g++ (Ubuntu 7.4.0-1ubuntu1~18.04.1) 7.4.0

$ nm ./a.out  | grep pthread_mutex_lock
0000000000407010 T __pthread_mutex_lock
00000000004069d0 t __pthread_mutex_lock_full
0000000000407010 W pthread_mutex_lock

总结一下:

Ubuntu 14.04& 16.04:T pthread_mutex_lock(强符号)
Ubuntu 18.04:W pthread_mutex_lock(弱符号)

Ubuntu 14.04 & 16.04: T pthread_mutex_lock (strong symbol)
Ubuntu 18.04: W pthread_mutex_lock (weak symbol)

在更复杂的示例中，这可能会导致分段错误.例如，在此代码中(可以在

In a more complex example, this can lead to Segmentation faults. For example, in this code (the unmodified file can be found here):

#include <pthread.h>
#include <thread>
#include <cstring>
#include <iostream>
#include <mutex>
#include <thread>
#include <vector>

std::mutex mutex;

void myfunc(int i) {
    mutex.lock();
    std::cout << i << " " << std::this_thread::get_id() << std::endl << std::flush;
    mutex.unlock();
}

int main(int argc, char **argv) {
    std::cout << "main " << std::this_thread::get_id() << std::endl;
    std::vector<std::thread> threads;
    unsigned int nthreads;

    if (argc > 1) {
        nthreads = std::strtoll(argv[1], NULL, 0);
    } else {
        nthreads = 1;
    }

    for (unsigned int i = 0; i < nthreads; ++i) {
        threads.push_back(std::thread(myfunc, i));
    }
    for (auto& thread : threads) {
        thread.join();
    }
}

尝试生成静态二进制文件失败，例如:

Attempts to produce a static binary failed, for example:

$ g++ thread_get_id.cpp -Wall -std=c++11 -O3 -static -pthread -Wl,--whole-archive -lpthread -Wl,--no-whole-archive
$ ./a.out
Segmentation fault (core dumped)

我尝试删除-O3，切换到clang++，切换到Gold链接程序，等等.但是它总是崩溃.根据我的理解，静态二进制文件崩溃的原因是基本功能(例如pthread_mutex_lock)不会以强符号结尾.因此，它们在最终二进制文件中丢失，从而导致运行时错误.

I tried to drop -O3, switching to clang++, switch to the Gold linker, etc. But it always crashes. From my understanding the reason for the crashes in the static binary is that essential functions (such as pthread_mutex_lock) do not end up as strong symbols. Thus, they are missing in the final binary, leading to runtime errors.

除了Ubuntu 18.04，我还可以在带有gcc 10.0.0的Arch Linux上重现相同的行为. 但是，在Ubuntu 14.04和16.04上，可以创建和执行静态二进制文件，而不会出现任何错误.

Apart from Ubuntu 18.04, I could also reproduce the same behavior on Arch Linux with gcc 10.0.0. However, on Ubuntu 14.04 and 16.04, the static binaries could be created and executed without any errors.

问题:

构建工具链中发生了哪些变化(在gcc 5.4.0和gcc 7.4.0之间)? (疯狂猜测:我看到了用于C11的pthread清理那时候.也许是原因吗?)
是回归，还是旧的解决方法不再正确?
如果没有回归，应该怎么做才能允许静态链接到pthread?

What changed in the build toolchain (between gcc 5.4.0 and gcc 7.4.0)? (Wild guess: I saw a pthread cleanup for C11 that falls in that time. Maybe that is the reason?)
Is it a regression, or is the old workaround no longer correct.
If it is no regression, what should be done instead to allow static linking to pthread?

GCC:用于静态链接到pthread的--whole-archive配方在最新的gcc版本中停止工作 [英] GCC: --whole-archive recipe for static linking to pthread stopped working in recent gcc versions

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GCC:用于静态链接到pthread的--whole-archive配方在最新的gcc版本中停止工作 [英] GCC: --whole-archive recipe for static linking to pthread stopped working in recent gcc versions

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