Optimize stack usage of Dispatch::poll #6
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Dispatch::poll has to copy the request so that the app can write the response to the interchange. Previously, we called Responder::take_request to obtain the message out of the interchange. This implementation had a stack usage of 15280 bytes while the message size is only 7609 bytes. With this patch, we only request a reference from the responder and manually copy the message to a buffer. This reduces the stack size to 7664 bytes. I have no idea why the take_request implementation creates an additional copy of the message. But as this function is the root for all CTAPHID commands, this means we can save around 7 kB stack virtually everywhere. Similar optimizations may be possible in other functions too.
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Already reviewed and approved in Nitrokey#1. |
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Dispatch::poll has to copy the request so that the app can write the response to the interchange. Previously, we called Responder::take_request to obtain the message out of the interchange. This implementation had a stack usage of 15280 bytes while the message size is only 7609 bytes.
With this patch, we only request a reference from the responder and manually copy the message to a buffer. This reduces the stack size to 7664 bytes.
I have no idea why the take_request implementation creates an additional copy of the message. But as this function is the root for all CTAPHID commands, this means we can save around 7 kB stack virtually everywhere. Similar optimizations may be possible in other functions too.