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我正在尝试写一个简单的“你好，世界！” 在 x86_64 上使用马赫线程的程序。不幸的是，程序在我的机器上因分段错误而崩溃，我似乎无法解决这个问题。我在网上找不到太多关于 Mach 线程的文档，但我参考了以下C 文件，该文件也使用了 Mach 线程。

据我所知，我做的一切都是正确的。我怀疑分段错误是因为我没有正确设置线程的堆栈，但我采取了与参考文件相同的方法，其中包含以下代码。

// This is for alignment. In particular note that the sizeof(void*) is necessary
// since it would usually specify the return address (i.e. we are aligning the call
// frame to a 16 byte boundary as required by the abi, but the stack pointer
// to point to the byte beyond that. Not doing this leads to funny behavior on
// the first access to an external function will fail due to stack misalignment
state.__rsp &= -16;
state.__rsp -= sizeof(void*);

你知道我做错了什么吗？

#include <cstdint>
#include <iostream>
#include <system_error>

#include <unistd.h>
#include <mach/mach_init.h>
#include <mach/mach_types.h>
#include <mach/task.h>
#include <mach/thread_act.h>
#include <mach/thread_policy.h>
#include <mach/i386/thread_status.h>

void check(kern_return_t err)
{
        if (err == KERN_SUCCESS) {
                return;
        }

        auto code = std::error_code{err, std::system_category()};
        switch (err) {
        case KERN_FAILURE:
                throw std::system_error{code, "failure"};
        case KERN_INVALID_ARGUMENT:
                throw std::system_error{code, "invalid argument"};
        default:
                throw std::system_error{code, "unknown error"};
        }
}

void test()
{
        std::cout << "Hello from thread." << std::endl;
}

int main()
{
        auto page_size = ::getpagesize();
        auto stack = new uint8_t[page_size];
        auto thread = ::thread_t{};
        auto task = ::mach_task_self();
        check(::thread_create(task, &thread));

        auto state = ::x86_thread_state64_t{};
        auto count = ::mach_msg_type_number_t{x86_THREAD_STATE64_COUNT};
        check(::thread_get_state(thread, x86_THREAD_STATE64,
                (::thread_state_t)&state, &count));

        auto stack_ptr = (uintptr_t)(stack + page_size);
        stack_ptr &= -16;
        stack_ptr -= sizeof(void*);

        state.__rip = (uintptr_t)test;
        state.__rsp = (uintptr_t)stack_ptr;
        state.__rbp = (uintptr_t)stack_ptr;
        check(::thread_set_state(thread, x86_THREAD_STATE64,
                (::thread_state_t)&state, x86_THREAD_STATE64_COUNT));

        check(::thread_resume(thread));
        ::sleep(1);
        std::cout << "Done." << std::endl;
}

参考文件使用C++11；如果使用 GCC 或 Clang 编译，则需要提供std=c++11标志。

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