如何将 __attribute__((section(“name”))) 用于 per-cpu 全局变量

Question

I have come accross code that uses __attribute__((section(“name”))) for per cpu global variables. I have searched about it and have come to know that it is used for placing the data at a specified memory location with the help of linker scripts. What I do not understand is how it can be used for per-cpu data - that is, if a global variable is placed inside a section defined with __attribute__((section(“name”))) , then every cpu has its own copy of this global variable. I may be wrong, but my intuition is that linker scripts are used along with __attribute__((section)) to make this happen. But I do not know how. A small working example, or a hint of how to realize this in code would be great.

Note: this question is with respect to the C language.

Answer 1

The operating system/kernel initializes the hardware in such a way that the data at this memory location is not globally shared, but specific to each CPU. Presumably, this is achieved by having slightly different page tables installed on each CPU. All the section attribute does is place the variable into that special memory region, but once the underlying hardware is configured to enable the lack of cross-CPU sharing, this is all it takes to make a variable CPU-specific.