encoding, core: Add find_watchpoint() and encoding

[linD026]

Add the implementation of find_watchpoint().

Since the 64-bit architecture, the virtual address only uses the least
57 bit. So we can let the watchpoint store the information, like
operation type and object size, on the 64 to 57 bit.

Signed-off-by: Chih-En Lin shiyn.lin@gmail.com

[linD026]

@ziyuan1135
Please check if the patch does not conflict with your thought.

[linD026]

@ziyuan1135
Could you please help me check this PR?

[linD026]

watchpoints(array)裡面存的應該是mem. address，element type為atomic long(64bits) 所以應該是watchpoint = watchpoints[slot + i]就好了？

If we want to get the value at this line, we need to use the atomic read.
like:

v = atomic_read(&watchpoints[slot + i]);

Then, determine whether the value is registered or not by direct access.

if (v & SOME_FLAGS)
    do_something();

But, we cannot promise that the value we read is synchronous with the corresponding value in the watchpoints array.

For example, thread B register after thread A get the value but doesn't check yet.

// thread A
v = atomic_read(&watchpoints[slot + i]);

// thread B
atomic_set((&watchpoints[slot + i], 1);

// thread A
// non-synchronous here
if (v & SOME_FLAGS)
    do_something();

It needs to handle more corner cases when we use this method.

不應該是拿watchpoints(array)這個mem. address嗎？ 即watchpoint = &watchpoints[slot + i] 如果有理解錯，再跟我說一下，感謝

So, at this point, we will first get the address of the index of watchpoints array, and use the
atomic RMW operation to access it.
And that is why we first get the address here.

[linD026]

我剛剛的問題是在[bd693d1]這邊。程式碼的部分：core.c第78行 這邊想問，這個find_watchpoint func.是可以直接用的嗎? 還是我需要在加東西

You can directly use it.
It doesn't need to add anything if you only want to find the watchpoint that is registered or not.

[linD026]

It seems like the PR doesn't conflict with your mind.