Joseph Ferano
6ebcea6d3a
flan_dev_reg_dead was reaching for the containment scan, and it is on the free path: a dev build would have paid a 4096-entry sweep per free. A free hands back the base address the allocator gave out, which is what the slot is keyed on, so the question there is equality and never containment. Only free-all needs the scan, and that runs once a frame. The table is allocated when it is armed, not declared. A fixed array was a quarter of a megabyte of BSS in a shipped game for a table that build never writes; now a release build carries a null pointer and the not-taken branch. The pointer arm binds its subject to a slot before naming it three times — the slice arm's rule, and its reason: an inspect with a path reaches a leaf through a bounds check, and three of those to render one pointer is the walk paying for its own shape. dev-ptr.flan shows both halves on a stopped stack. It was read by hand; the test_dev.ml case that would drive it is another lane's file, and NEXT.md says so.
47 lines
1.6 KiB
Plaintext
47 lines
1.6 KiB
Plaintext
;;;; A stopped stack holding two pointers into Vec storage, one of which is
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;;;; already dead. The allocation registry is what lets the inspector tell
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;;;; them apart, and this is the program that shows it:
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;;;;
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;;;; ("live" "(Ptr Enemy)" "<ptr (Enemy {.hp 41 .x 2})>")
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;;;; ("dead" "(Ptr Enemy)" "<ptr dead: was Enemy, freed at step 15>")
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;;;;
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;;;; Both lines are what `(:op "locals" :frame 1)` answers with today, and
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;;;; both were read off a running session by hand. **No test drives this
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;;;; program yet**: the case belongs beside the other `locals` and `inspect`
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;;;; cases in test_dev.ml, which is another lane's file. NEXT.md says so
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;;;; rather than letting the verification read as automated.
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;;;;
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;;;; Why a Vec rather than a struct on the stack: a stack address is not in
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;;;; the registry by design — the shadow stack already answers for a local by
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;;;; name — so a pointer to one renders <ptr>, which is neither half of what
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;;;; this is demonstrating.
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(import agent "vendor:agent")
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(defstruct Boom [why i32])
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(defstruct Enemy [hp i32 x i32])
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(defn deeper [] i64
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(restart-case
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(do (error (Boom {.why 7})) 1)
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(carry-on [] 5)))
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(defn outer [] i64
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(let [v (vec-new Enemy)
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w (vec-new Enemy)]
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(push v (Enemy {.hp 41 .x 2}))
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(push w (Enemy {.hp 7 .x 9}))
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(let [live (addr (at v 0))
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dead (addr (at w 0))]
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(free w)
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(deeper))))
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(defvar ticks i64)
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(defn main [] i32
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(agent/start "/tmp/flan-ptr-fallback.sock")
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(print (outer)) (println "")
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(dotimes [i 4000]
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(agent/wait 5)
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(set ticks (+ ticks 1)))
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0)
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