Re: Why does tail call only unwind the current stack frame instead of resetting the current stack?

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No, I didn't hit this limit.

The current implementation already keeps tracks of the number of tail calls which to me is the same effort of tracking the stack size. I was just wondering if there's any fundamental reason that you can't reset the stack directly. But it seems that there is not.

Thanks

On 9/12/21 11:08 PM, Yonghong Song wrote:


On 9/12/21 10:48 AM, Hsuan-Chi Kuo wrote:
Hi,

The function check_max_stack_depth (https://elixir.bootlin.com/linux/latest/source/kernel/bpf/verifier.c#L3574 ) is used to ensure the stack size is no greater than 8KB.

The stack can only grow over 8KB because of tail calls as they only unwind the current stack frame. I wonder why not make tail call reset the stack since what was on the stack

will never be used again?

I think this is just an artifact of current implementation.
To do a correct reset of the stack, additional instructions
are needed to keep track and accumulate stack size properly,
so when a tail call is reached, it knows how much stack size
to reset.

Did you hit this limitation? Could you describe your use case
in detail?



Thanks




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