这不是对问题的直接回答，但这是对评论中出现的一个问题的回答。本质上，问题是硬件对多核操作提供了什么支持，即同时运行多个软件线程的能力，而无需在它们之间进行软件上下文切换。(有时称为SMP系统)。

Nicholas Flynt had it right, at least regarding x86. In a multi-core environment (Hyper-threading, multi-core or multi-processor), the Bootstrap core (usually hardware-thread (aka logical core) 0 in core 0 in processor 0) starts up fetching code from address 0xfffffff0. All the other cores (hardware threads) start up in a special sleep state called Wait-for-SIPI. As part of its initialization, the primary core sends a special inter-processor-interrupt (IPI) over the APIC called a SIPI (Startup IPI) to each core that is in WFS. The SIPI contains the address from which that core should start fetching code.

这种机制允许每个核心从不同的地址执行代码。所需要的只是为每个硬件核心提供软件支持，以便建立自己的表和消息队列。

操作系统使用它们来执行软件任务的实际多线程调度。(一个正常的操作系统只需要在启动时启动一次其他内核，除非你是热插拔cpu，例如在虚拟机中。这与启动或将软件线程迁移到这些内核是分开的。每个核心都在运行内核，如果没有其他事情要做，内核就会调用sleep函数来等待中断。)

就实际的程序集而言，正如Nicholas所写的，单线程应用程序集和多线程应用程序集之间没有区别。每个核都有自己的寄存器集(执行上下文)，因此编写:

mov edx, 0

将只更新当前运行线程的EDX。没有办法使用单一的汇编指令在另一个处理器上修改EDX。您需要某种类型的系统调用来要求操作系统告诉另一个线程运行将更新自己的EDX的代码。

汇编代码将转换为将在一个核心上执行的机器代码。如果你希望它是多线程的，你将不得不使用操作系统原语在不同的处理器上多次启动这段代码，或者在不同的核上启动不同的代码段——每个核将执行一个单独的线程。每个线程只能看到当前正在执行的一个内核。

根据我的理解，每个“核心”都是一个完整的处理器，有自己的寄存器集。基本上，BIOS启动时只运行一个核心，然后操作系统可以通过初始化其他核心并将它们指向要运行的代码等方式“启动”其他核心。

同步由操作系统完成。通常，每个处理器为操作系统运行不同的进程，因此操作系统的多线程功能负责决定哪个进程可以访问哪个内存，以及在内存碰撞的情况下该做什么。

非官方的SMP FAQ

曾经，为了编写x86汇编程序，例如，你会有这样的指令:“用值5加载EDX寄存器”，“增加EDX”寄存器，等等。对于拥有4核(甚至更多)的现代cpu，在机器代码级别上，它是否看起来就像有4个独立的cpu(即只有4个不同的“EDX”寄存器)?

完全正确。有4组寄存器，包括4个单独的指令指针。

如果是这样，当你说“增加EDX寄存器”时，是什么决定哪个CPU的EDX寄存器被增加?

当然是执行指令的CPU。可以把它想象成4个完全不同的微处理器共享相同的内存。

现在在x86汇编器中有“CPU上下文”或“线程”概念吗?

不。汇编程序只是像往常一样翻译指令。没有变化。

内核之间的通信/同步是如何工作的?

由于它们共享相同的内存，这主要是程序逻辑的问题。虽然现在有一个处理器间中断机制，但它不是必要的，最初也没有出现在第一个双cpu x86系统中。

如果您正在编写一个操作系统，通过硬件公开的什么机制允许您在不同的内核上调度执行?

The scheduler actually doesn't change, except that it is slightly more carefully about critical sections and the types of locks used. Before SMP, kernel code would eventually call the scheduler, which would look at the run queue and pick a process to run as the next thread. (Processes to the kernel look a lot like threads.) The SMP kernel runs the exact same code, one thread at a time, it's just that now critical section locking needs to be SMP-safe to be sure two cores can't accidentally pick the same PID.

是一些特殊的特权指令吗?

不。这些核心都运行在相同的内存中，使用相同的旧指令。

如果你正在为一个多核CPU编写一个优化编译器/字节码虚拟机，你需要特别了解什么，比如说，x86，以使它生成跨所有核高效运行的代码?

运行与之前相同的代码。需要改变的是Unix或Windows内核。

你可以把我的问题总结为“为了支持多核功能，x86机器码做了哪些改变?”

没有什么是必要的。第一个SMP系统使用与单处理器完全相同的指令集。现在，x86体系结构已经有了很大的改进，并且有了大量的新指令来让事情变得更快，但是对于SMP来说没有一个是必要的。

For more information, see the Intel Multiprocessor Specification. Update: all the follow-up questions can be answered by just completely accepting that an n-way multicore CPU is almost1 exactly the same thing as n separate processors that just share the same memory.2 There was an important question not asked: how is a program written to run on more than one core for more performance? And the answer is: it is written using a thread library like Pthreads. Some thread libraries use "green threads" that are not visible to the OS, and those won't get separate cores, but as long as the thread library uses kernel thread features then your threaded program will automatically be multicore. 1. For backwards compatibility, only the first core starts up at reset, and a few driver-type things need to be done to fire up the remaining ones.2. They also share all the peripherals, naturally.

The main difference between a single- and a multi-threaded application is that the former has one stack and the latter has one for each thread. Code is generated somewhat differently since the compiler will assume that the data and stack segment registers (ds and ss) are not equal. This means that indirection through the ebp and esp registers that default to the ss register won't also default to ds (because ds!=ss). Conversely, indirection through the other registers which default to ds won't default to ss.

The threads share everything else including data and code areas. They also share lib routines so make sure that they are thread-safe. A procedure that sorts an area in RAM can be multi-threaded to speed things up. The threads will then be accessing, comparing and ordering data in the same physical memory area and executing the same code but using different local variables to control their respective part of the sort. This of course is because the threads have different stacks where the local variables are contained. This type of programming requires careful tuning of the code so that inter-core data collisions (in caches and RAM) are reduced which in turn results in a code which is faster with two or more threads than it is with just one. Of course, an un-tuned code will often be faster with one processor than with two or more. To debug is more challenging because the standard "int 3" breakpoint will not be applicable since you want to interrupt a specific thread and not all of them. Debug register breakpoints do not solve this problem either unless you can set them on the specific processor executing the specific thread you want to interrupt.

其他多线程代码可能涉及在程序的不同部分运行的不同线程。这种类型的编程不需要同样的调优，因此更容易学习。

这不是对问题的直接回答，但这是对评论中出现的一个问题的回答。本质上，问题是硬件对多核操作提供了什么支持，即同时运行多个软件线程的能力，而无需在它们之间进行软件上下文切换。(有时称为SMP系统)。

Nicholas Flynt had it right, at least regarding x86. In a multi-core environment (Hyper-threading, multi-core or multi-processor), the Bootstrap core (usually hardware-thread (aka logical core) 0 in core 0 in processor 0) starts up fetching code from address 0xfffffff0. All the other cores (hardware threads) start up in a special sleep state called Wait-for-SIPI. As part of its initialization, the primary core sends a special inter-processor-interrupt (IPI) over the APIC called a SIPI (Startup IPI) to each core that is in WFS. The SIPI contains the address from which that core should start fetching code.

这种机制允许每个核心从不同的地址执行代码。所需要的只是为每个硬件核心提供软件支持，以便建立自己的表和消息队列。

操作系统使用它们来执行软件任务的实际多线程调度。(一个正常的操作系统只需要在启动时启动一次其他内核，除非你是热插拔cpu，例如在虚拟机中。这与启动或将软件线程迁移到这些内核是分开的。每个核心都在运行内核，如果没有其他事情要做，内核就会调用sleep函数来等待中断。)

就实际的程序集而言，正如Nicholas所写的，单线程应用程序集和多线程应用程序集之间没有区别。每个核都有自己的寄存器集(执行上下文)，因此编写:

mov edx, 0

将只更新当前运行线程的EDX。没有办法使用单一的汇编指令在另一个处理器上修改EDX。您需要某种类型的系统调用来要求操作系统告诉另一个线程运行将更新自己的EDX的代码。