mprotect 是否会刷新 ARM Linux 上的指令缓存？
我正在 ARM Linux 上编写一个 JIT，它执行包含自修改代码的指令集。该指令集没有任何缓存刷新指令（在这方面与 x86 类似）。
如果我向某个页面写入一些代码，然后在该页面上调用 mprotect，这是否足以使指令缓存失效？或者我还需要在这些页面上使用 cacheflush 系统调用吗？
I am writing a JIT on ARM Linux that executes an instruction set that contains self-modifying code. The instruction set does not have any cache flush instructions (similar to x86 in that respect).
If I write out some code to a page and then call mprotect on that page, is that sufficient to invalidate the instruction cache? Or do I also need to use the cacheflush syscall on those pages?
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您希望 mmap/mprotect 系统调用将建立立即更新的映射，并且不需要进一步交互即可使用指定的内存范围。我看到内核确实刷新了 mprotect 上的缓存。在这种情况下，不需要刷新缓存。
但是，我还发现某些版本的 libc 确实在
mprotect之后调用cacheflush，这意味着某些环境需要刷新缓存（或者以前有过）。我猜测这是一个错误的解决方法。您始终可以添加对cacheflush的调用；虽然它是额外的代码，但它不应该是有害的——最坏的情况是，缓存已经被刷新了。您总是可以编写一个快速测试，看看会发生什么......
You'd expect that the mmap/mprotect syscalls would establish mappings that are updated immediately, and need no further interaction to use the memory ranges as specified. I see that the kernel does indeed flush caches on mprotect. In that case, no cache flush would be required.
However, I also see that some versions of libc do call
cacheflushaftermprotect, which would imply that some environments would need the caches flushed (or have previously). I'd take a guess that this is a workaround to a bug.You could always add the call to cacheflush; although it's extra code, it shouldn't be to harmful - at worst, the caches will already be flushed. You could always write a quick test and see what happens...
特别是在 Linux 中，mprotect 至少从 2.6.39 版本（甚至更早版本）开始对所有缓存进行缓存刷新。你可以在代码中看到：
https://elixir.bootlin.com/ linux/v2.6.39.4/source/mm/mprotect.c#L122 。
如果您正在编写 POSIX 可移植代码，我会调用 cacheflush，因为标准 C 库不要求内核或实现执行此类行为。
编辑：您还应该小心并检查
flush_cache_range在您正在实现的特定体系结构中执行的操作，因为在某些体系结构（如 ARM64）中该函数不执行任何操作...In Linux specifically, mprotect DOES cacheflush all caches since at least version 2.6.39 (and even before that for sure). You can see that in the code:
https://elixir.bootlin.com/linux/v2.6.39.4/source/mm/mprotect.c#L122 .
If you are writing a POSIX portable code, I would call cacheflush as the standard C library is not demanding such behavior from the kernel, nor from the implementation.
Edit: You should also be carefull and check what
flush_cache_rangedoes in the specific architecture you are implementing for, as in some architecture (like ARM64) this function does nothing...我相信您不必显式刷新缓存。
这是哪个处理器？ ARMv5？ ARMv7？
I believe you do not have to explicitly flush the cache.
Which processor is this? ARMv5? ARMv7?