Calculating it earlier is a micro-optimization that doesn't seem like it
matters at all compared to all other costs of spawning a process. But at
the same time it makes things more fragile. And in fact bootstrap
actually passed the wrong value. It passed the
total_args_envs_auxvpointee_size that it computed rather than the
total_args_envs_size. While over-approximation doesn't cause UB, it
unnecessarily increases the amount of memory used after exec.
In addition pass &[&[u8]] rather than iterators for args and envs to
enable precomputing the total arg and env size. This also prevents you
from forgetting to pass a reversed iterator.
bjorn3
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