zkalloc fix: safe arena routing#215
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Barnadrot/zk-alloc#9) (replaces the "flush_rayon" ugly fix) Co-authored-by: Barnadrot <kbarna.drot@gmail.com>
) - realloc: switch copy_nonoverlapping -> copy. When a Vec grows inside the arena, the freshly-bumped destination can overlap the source within the same slab, violating copy_nonoverlapping's precondition (UB). - begin_phase: panic if a phase is already active. Phases must stay flat in a bump allocator: a nested begin would recycle the slab and overwrite the outer phase's still-live data. Rather than refcounting (per PR #10), we make the violation impossible via an assert. Co-authored-by: Barnadrot <kbarna.drot@gmail.com>
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Profile attributes 1.30% of P-core cycles to libc allocator helpers (_int_malloc + cfree + malloc) inside the zk-alloc build — those are sub-MIN_ARENA_BYTES allocations being routed to System during the active phase. Lowering the floor pulls the 1024..4095-byte band back into the bump-pointer fast path; ideally we recover most of that 1.30%. Why this is still phase-crossing safe: - The ~1.5 KB crossbeam_deque::Injector blocks named in the original comment fall in [0, 1024), so they still route to System. - Sticky-System realloc (PR leanEthereum#215) keeps any Vec that was first allocated in System in System through growth — a Vec allocated at 64 B and grown to 4 KiB inside a phase stays in System. - The known phase-crossing patterns (Registry slots, HashMap entries, rayon job frames) are all sub-KB per the comment; they remain routed to System. Risk: if there is a phase-crossing allocation in the 1024..4095-byte band we have not enumerated, it will end up in arena memory and be recycled across phase boundaries. Correctness gate must pass before benchmark, and prove_loop's 5-warm-proof pattern is the same shape that would expose such a bug.
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(size-routing + sticky-System realloc) (mirors Barnadrot/zk-alloc#9)
(replaces the "flush_rayon" ugly fix)