Joseph Ferano
5a62770e52
A defclass is a named dyn map with a shape tag, and a generic function
dispatches on it two ways: CLOS's, where the dispatch value is the class
of the first argument, and Clojure's, where a body computes it. They are
one mechanism and not two — a class dispatcher is (class-of arg0) as the
dispatch function, which is what lets a method written for the class
point and one written for the value :point be the same branch.
(defclass point [x y])
(point 3 4) ; the constructor, positional
(class-of p) ; :point, or nil for anything else
(defgeneric area [self] dyn)
(defmethod area point [p] (* (get p :x) (get p :y)))
(defmulti describe [x] dyn (get x :kind))
(defmethod describe :square [s] ...)
(defmethod describe :else [s] ...)
A slot is a key in the instance's own map, so get, put and has-key? are
how one is read and written and no operation was added for any of it.
What the class adds is the tag, and the tag lives in the object's header
rather than in a reserved entry — the queue's note said a reserved key
and this departs from it, because a key would be counted by len, walked
by the renderer and compared by equality, so every instance would answer
a length one larger than its slot count and print a key nobody wrote. A
header field cannot be reached by get or put at all, so no user key can
collide with it. It costs nothing: the map arm of flan_obj's union grows
to the size the view arm already had, and sizeof(flan_obj) is unchanged.
It needs no tracing either — the tag is an interned keyword entry, which
is immortal and is not a collector object.
The tag shows up in exactly three places: class-of answers it, equality
compares it (two instances of one class compare by their slots; an
instance and a plain map with the same entries do not, which is
Clojure's answer for a record beside a map), and both renderers print it
— #point{ :x 1 :y 2}, Clojure's own spelling.
None of the four forms reaches the checker. lib/classes.ml turns the
whole declaration list into ordinary defns at the top of build_program,
the way Shim.expand already turns a declare-c into a declare plus a
defn: a class becomes its constructor, a generic becomes one function
whose body binds the dispatch value and compares it down a chain, and a
method becomes a branch of that chain. It is a pass and not a macro
because a macro sees one form and the generic's body is not decidable
until every method is in hand — a method may be written above its
generic, below it, or arrive at a reload an hour later.
That last case is why the method bodies are inlined rather than lifted.
A generic is exactly one top-level name, so adding a method to a running
program is the ordinary redefinition of one function, through the cell
every call site already goes through. session.ml names the generic
alongside the method's own declaration name for that reason. The cost,
recorded rather than hidden: a method is not separately callable and is
not a frame of its own.
A dispatch that finds no method signals NoMethod, a prelude struct
carrying the generic's name and the dispatch value that missed. A
condition and not a trap, because a miss is something a program can be
written to answer, and handler-case around the call is the shape. Its
value field is dyn, the first condition here with one; the per-type
descriptor an item-2 struct carries is what the collector reaches it by.
No restart is established at the miss, which is BoundsError's decision
taken for BoundsError's reason.
Both backends, identically: the two new runtime entry points are
declared in emit.ml and the x86 backend needs nothing, since a dyn call
is a dyn call there. Deferred and written down in FIX.org: inheritance,
multi-argument dispatch, :before/:after/:around, named-slot
construction, unknown-slot checking, and computed dispatch values.
442 lines
23 KiB
OCaml
442 lines
23 KiB
OCaml
(* The corpus a second time, under AddressSanitizer and
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UndefinedBehaviorSanitizer.
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Not part of [dune test] and deliberately so: a sanitized build of one
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program is a 1.8MB statically linked binary and takes ten to twenty seconds
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to produce, so the sweep is minutes where the whole existing suite is
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seconds. It has its own alias.
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dune build --root . @sanitize
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What this can and cannot see is written down in [Build.opts] and in
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[Emit]'s [sanitize] comment, and it is not symmetric:
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- ASan reaches Flan code, but only because [Emit] puts [sanitize_address]
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on every function it defines; the attribute is what the pass selects on
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and hand-written IR has none by default. The positive control for that is
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[oob], below, which must report.
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- UBSan reaches the runtime's C and nothing else. Its checks are branches
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clang's *frontend* emits, and no attribute asks an LLVM pass to produce
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them, so the shift-past-the-width and float-cast questions this sweep was
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partly meant to answer are not answerable this way. [shift] records that
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as a test rather than as a paragraph: it is a program with unambiguous
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shift UB in it, and it is expected *not* to be caught.
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The check is two-sided. A marker in the sanitized run's output is a
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failure, and so is any divergence from the unsanitized run — same output,
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same exit status. The second half is not redundant: UBSan recovers by
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default, so a program can trip a check, carry on with a different value and
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still exit 0, and several of these programs exit nonzero by design, so
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"exit status 0" is not available as a pass condition. *)
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open Flan
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(* The watchdog first: a hang is the one failure mode that reports
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nothing at all. See watchdog.ml. *)
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let () = Watchdog.arm ~seconds:3600 "test_sanitize"
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let failures = Test_support.failures
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let fail fmt = Test_support.fail fmt
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let scratch = Test_support.scratch
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(* Leaks are off. Every allocation in the runtime is allocate-once-never-free
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by design — [rt_args] says so in its own comment — so LeakSanitizer here
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produces a suppression list and no information. Set in the environment
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rather than baked in, so a session asking the leak question can ask it.
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[print_stacktrace] is what turns a UBSan report from a source line into
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something with a caller in it, and it is off by default. *)
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let env =
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"ASAN_OPTIONS=${ASAN_OPTIONS:-detect_leaks=0} \
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UBSAN_OPTIONS=${UBSAN_OPTIONS:-print_stacktrace=1} "
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let run exe args =
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let out = Filename.concat scratch "flan-sanitize.out" in
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let cmd =
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Printf.sprintf "%s%s %s > %s 2>&1" env (Filename.quote exe)
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(String.concat " " (List.map Filename.quote args))
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(Filename.quote out)
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in
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let code = Sys.command cmd in
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let text = In_channel.with_open_bin out In_channel.input_all in
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(try Sys.remove out with Sys_error _ -> ());
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(code, text)
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let compile ~sanitize ~checks path =
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let exe =
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Filename.concat scratch
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(Printf.sprintf "flan-san-%s-%s"
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(if sanitize then "s" else "p")
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(Filename.remove_extension (Filename.basename path)))
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in
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let p, csrcs, lflags = Test_support.linked path in
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ignore
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(Build.executable
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~opts:{ Build.default with checks; sanitize } ~csrcs ~lflags p ~out:exe);
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exe
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let contains = Test_support.contains
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(* What a report looks like, whichever sanitizer wrote it. *)
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let markers =
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[ "ERROR: AddressSanitizer"; "runtime error:"; "ERROR: LeakSanitizer";
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"SUMMARY: UndefinedBehaviorSanitizer" ]
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let reported text = List.exists (contains text) markers
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(* The corpus. Excluded, with the reason, rather than quietly absent:
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- raylib-*, and the windowed examples, because raylib and libm are not
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instrumented and every report through them would be about somebody
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else's code.
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- break.flan and agent.flan, which stop in the break loop and wait for an
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editor to connect. They are covered by test_agent against a real daemon.
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- the dev-* and reload-* programs, which need a host process or a dlopen
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harness. The reload path is half-covered at best in any case: a
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redefinition module is built by llc and ld, not by clang, so nothing
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instruments it — one more thing this sweep does not prove.
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- nth-gone, pkg-hidden-main, pkg-two-aliases, pkg-two-mains, pkg-cycle,
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which are negative cases and are expected not to compile.
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calc-me is here and is not in test/programs: it is the one string parser in
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the corpus, which makes it the likeliest to push [scratch] or [escaped]
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anywhere near their bounds. *)
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let corpus =
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[ (* bounds.flan selects its case from argv, and every case but 0 is one
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that traps. Argument 0 is the in-bounds path — the last index of a
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fixed array, a slice ending exactly at len, an empty slice at len —
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which is the one the sweep has something to say about. The trapping
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cases are where the ASan-without-bounds-checks question lives and they
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are run separately; see [unchecked_controls]. Running this program with
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*no* argument reads args[1] of a one-element argv, which is a bug in
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the harness rather than in anything under test. *)
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"programs/bounds.flan", [ "0" ];
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"programs/arena-value.flan", [];
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(* Here for what it would catch rather than for what it prints: the three
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number conversions render into a frame slot the checker allocates per
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call site, and a slot that ended up as a reclaimed temporary instead
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would be a stack-use-after-scope — which is exactly what ASan sees and
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an output comparison does not. *)
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"programs/two-numbers.flan", [];
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"programs/bytes2.flan", [];
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"programs/cleanup.flan", [];
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"programs/conditions.flan", [];
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"programs/debug.flan", [];
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"programs/debug-permuted.flan", [];
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"programs/destructure.flan", [];
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"programs/edn.flan", [];
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(* The copy edn/read makes of every string: the document is read out of a
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(Vec u8) that is then overwritten in place, so a reader still holding
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views is reading a buffer it does not own and ASan is what says so. *)
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"programs/edn-read.flan", [];
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"programs/enum-compare.flan", [];
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"programs/error.flan", [];
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(* Makes and removes its own tree, so the two runs of the sweep see the
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same directory; the new C here is three more path buffers, which is
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exactly what this tool is for. *)
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"programs/files.flan", [];
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(* The unwinding handler, and here for the frames rather than for the heap:
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every path it takes leaves a function through the transfer exit, where
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a handler frame or a restart frame left on its stack is a pointer into
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an alloca that has gone. An output comparison cannot see that until
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something later calls through it; ASan sees it at the store. The
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with-allocator case is the one that reaches the heap — the region it
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rebound is released after the unwind has carried a value out of it. *)
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"programs/handler-case.flan", [];
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(* The same transfer exit, asked about the defers rather than the frames.
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The bug this program was written for was a defer running over a binding
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the form that would have written it had transferred out of, and the
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cleanup was a free: the second run of that path frees a pointer nobody
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stored. ASan is the regression guard and not the detector — an
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uninitialised stack slot is not its bug class, and it reported nothing
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on the broken binary; what named it was valgrind, and test_valgrind.ml
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runs this program for that reason. *)
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"programs/init-conditions.flan", [];
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(* The JSON reader, which is the corpus's densest allocator: every string
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in the document is a (Vec u8) grown a byte at a time and then handed
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out as a view of its own block, and the block is never freed because
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the view IS the answer. ASan is what says the view still points at the
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block after the growth that moved it. *)
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"programs/json.flan", [];
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"programs/machine.flan", [];
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"programs/math.flan", [];
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"programs/math3.flan", [];
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"programs/pkg-diamond.flan", [];
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"programs/pkg-return.flan", [];
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"programs/pkg-shared.flan", [];
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"programs/pkg-unused.flan", [];
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"programs/printers.flan", [];
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"programs/println.flan", [];
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"programs/restarts.flan", [];
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(* The dyn programs, which reach flan_dyn.c from Flan rather than from the
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hand-written C below — and the difference is the whole reason they are
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here. [dyn_sweep] checks the collector against roots dyn_ops.c pushes
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by hand; these check it against the roots the *compiler* emits, which
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is the half no C test can reach. A root the emitter forgot is a live
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object swept, and that is a use-after-free with the collector's own
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hands on it.
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[dyn-vec] is the one that builds objects of three kinds; [dyn-defer]
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is the one whose roots come off on a transfer's path out rather than a
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return's, which is where a pop written on one path only would show.
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[p13] and [dyn-map] are the programs that allocate past flan_dyn.c's
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one-megabyte floor, so they are where a mark and a sweep
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actually run — everything else in this list agrees with ASan by never
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collecting at all. [dyn-map] is also the one whose live set is a map,
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so its keys and values are what the marker has to trace to be right,
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and the interned keywords are what the sweep has to leave alone. *)
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"programs/dyn-vec.flan", [];
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"programs/dyn-defer.flan", [];
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(* The per-type descriptors' own program, and the one in this list whose
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roots are aggregates rather than dyn words: a struct with a dyn field
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in a frame slot, in a global, in the temporary a by-value return lands
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in, and as a condition's payload across a handler transfer. It runs
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past the one-megabyte floor like [p13], so a mark and a sweep really
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happen, and what a wrong descriptor offset looks like is a read of a
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freed object — which is exactly what ASan is here to see and what no
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amount of reading the offsets can. *)
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"programs/dyn-struct.flan", [];
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"programs/dyn-map.flan", [];
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(* Classes, M2 queue item 6. A class instance is a map with one more word
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in its header, so what this adds over [dyn-map] is that word: it is
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written by a constructor, read by class-of, compared by equality and
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printed by both renderers, and it is the one field in an object that
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the marker deliberately does not trace — an interned keyword entry is
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immortal and is not a collector object. If that reasoning is wrong,
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50000 instances past the one-megabyte floor is where ASan says so. *)
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"programs/dyn-class.flan", [];
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(* nil <-> None at (Option T), M2 queue item 4: an Option's tag is read
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with a raw [Field] the surface language never writes (check.ml's
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[box_option]/[unbox_option], the same access Render's structural
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printer uses), so this is where a wrong tag offset or a wrong
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direction of the comparison shows up as a read past the struct rather
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than as a wrong answer. Both trap, by design — [nil-option] on a bare
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T meeting a dyn nil, [some-nil] on (Some nil) built from a value the
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checker could not see was nil — and the two-sided check above is what
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ASan's build being asked to trap the same way the plain build does. *)
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"programs/nil-option.flan", [];
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"programs/some-nil.flan", [];
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(* M2 item 3: a typed container's view. Mode 0, the survey — the modes
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that trap are exercised as C refusals in test_dyn.ml's [refuseview:*]
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instead, the same split [bounds.flan]'s "0" argument makes above. A
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view's storage is a plain array or a Vec's own malloc block, neither
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one this collector allocates, so there is nothing here for ASan to
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catch that the runtime tests above did not already exercise directly
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— this row is about the *compiler* lane: the address the checker
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hands the runtime at the crossing, and whether a push through the
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view that grows and moves the Vec leaves anything for ASan's
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use-after-free detection to find. *)
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"programs/dyn-view.flan", [ "0" ];
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"../spike/x86/p13-dyn-collect.flan", [];
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"programs/sand-headless.flan", [];
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"programs/signedness.flan", [];
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"programs/slices.flan", [];
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"programs/string-of-bytes.flan", [];
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"programs/text.flan", [];
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(* The clock and getenv. getenv hands back a slice viewing the process
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environment and never a copy, so a report here would be the one that
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matters. *)
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"programs/time.flan", [];
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"programs/unit-main.flan", [];
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"programs/utf8.flan", [];
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"programs/values.flan", [];
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"programs/virtual-controls-headless.flan", [];
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"../calc-me.flan", [ "1 + 2 * (3 - 0.5) / 2" ] ]
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let sweep ~checks label =
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List.iter
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(fun (path, args) ->
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match compile ~sanitize:false ~checks path with
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| exception Failure m -> fail "%s %s: unsanitized build: %s" label path m
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| plain ->
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(match compile ~sanitize:true ~checks path with
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| exception Failure m -> fail "%s %s: sanitized build: %s" label path m
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| san ->
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let c1, t1 = run plain args in
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let c2, t2 = run san args in
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if reported t2 then
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fail "%s %s: sanitizer report\n%s" label path t2
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else if c1 <> c2 || t1 <> t2 then
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fail "%s %s: diverged from the unsanitized run\n \
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plain (exit %d): %S\n sanitized (exit %d): %S"
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label path c1 t1 c2 t2;
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(try Sys.remove plain with Sys_error _ -> ());
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(try Sys.remove san with Sys_error _ -> ())))
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corpus
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(* The dyn runtime, under the same two sanitizers, driven from C. There are
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Flan programs that reach flan_dyn.c now and three of them are in [corpus]
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above — this used to say there were none — but they are a different
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question and not a replacement for this one. They exercise the roots the
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*compiler* emits, over the handful of operations a program happens to
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write; this exercises every entry point in the header, with the roots
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pushed by hand so that the runtime can be wrong on its own. The thing to
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build is test/dyn_ops.c against programs/dyn-host.flan — the same pair
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test_dyn.ml builds, with [sanitize] on.
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This is the case the sweep is most likely to have something to say about.
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Every other program in the corpus allocates and never frees, which is a
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policy ASan can only agree with; this one frees, and a mark-sweep collector
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is precisely a machine for freeing something that is still reachable. A
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use-after-free here is what a wrong marker looks like from the outside, and
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it is invisible to the assertions in test_dyn.ml — the freed bytes are
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usually still the bytes that were there.
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The leak question is not asked, for the reason [env] gives: leaks are off
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across this file because the runtime's allocations are allocate-once by
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design. It would be the wrong question here anyway — the temporaries ring
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holds the last sixty-four objects alive on purpose and at exit, and every
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one of them would be reported.
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Only the modes that return are run. The refusals end in [_exit(134)], which
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skips ASan's exit-time checks entirely, so running them would prove nothing
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the checked build has not already proved. *)
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let dyn_sweep () =
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let exe = Filename.concat scratch "flan-san-dyn" in
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let path = "programs/dyn-host.flan" in
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let p, csrcs, lflags = Test_support.linked path in
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match
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Build.executable
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~opts:{ Build.default with Build.sanitize = true }
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~csrcs:(csrcs @ [ "dyn_ops.c" ]) ~lflags p ~out:exe
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with
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| exception Failure m -> fail "dyn: sanitized build: %s" m
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| _ ->
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List.iter
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(fun mode ->
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let code, text = run exe [ mode ] in
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if reported text then fail "dyn %s: sanitizer report\n%s" mode text
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else if code <> 0 then
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fail "dyn %s: exit %d under the sanitizers\n%s" mode code text)
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[ "ops"; "gc"; "unrooted"; "desc"; "nested"; "sharing"; "park" ];
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(try Sys.remove exe with Sys_error _ -> ())
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(* The positive controls, which are the only evidence that a clean sweep means
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anything. Both are written here rather than kept in test/programs because
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neither is a program anybody should build: one reads off the end of an
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array and the other shifts an i32 by 32. *)
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let control ~expect_report ?(args = []) ~why name src =
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let path = Filename.concat scratch (name ^ ".flan") in
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Out_channel.with_open_bin path (fun ch -> Out_channel.output_string ch src);
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let exe = compile ~sanitize:true ~checks:false path in
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let _, text = run exe args in
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(match expect_report, reported text with
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| true, false -> fail "control %s: nothing reported. %s\n%s" name why text
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| false, true -> fail "control %s: reported. %s\n%s" name why text
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| _ -> ());
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(try Sys.remove exe with Sys_error _ -> ());
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(try Sys.remove path with Sys_error _ -> ())
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(* The variant the checked build cannot ask for: with Flan's own bounds checks
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off, is ASan enough on its own? bounds.flan is the program to ask it with —
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every one of its selectors is a deliberate out-of-bounds access, and in a
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checked build every one of them traps.
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The answer is no, and it is worth having the shape of the no. [reports]
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holds the cases ASan catches; the rest are listed with why it does not, and
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they are printed rather than asserted, because a future LLVM that folds
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differently would change them and that is information, not a regression.
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[9] is the one that is not about ASan at all: at -O2 the access never
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happens. The index is out of bounds on an [inbounds] getelementptr into a
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string constant, so the whole load folds to zero and the program prints a
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wrong answer instead of touching a redzone. At -O0, with the load still in
|
|
the program, ASan reports it. That divergence is why [--sanitize] does not
|
|
force -O0 the way [--debug] does — the optimiser is half of what is being
|
|
measured. *)
|
|
let unchecked_controls () =
|
|
let reports = [ "3"; "7"; "4" ] in
|
|
let silent =
|
|
[ "-1", "a negative index into a global. Not a property of the access: \
|
|
ASan lays a global out as {data, redzone}, so an underflow is \
|
|
caught when something redzoned precedes it and not when nothing \
|
|
does — measured both ways, and here nothing does. Whether \
|
|
reading before an array is seen at all is therefore up to what \
|
|
the linker put in front of it";
|
|
"9", "at -O2 the load is folded away — an out-of-bounds inbounds GEP \
|
|
into a string constant is poison, so nothing is read and a wrong \
|
|
value is printed. Reported at -O0.";
|
|
"2", "a reversed slice (lo 2, hi 1), which this build traps on before \
|
|
anything is read. It is in this list rather than out of it \
|
|
because it used to be here for the opposite reason: the length \
|
|
came out negative, nothing was read, and ASan had nothing to \
|
|
see, which made a slice with a negative length reaching user \
|
|
code a checker question and not a sanitizer one. The checker \
|
|
answered it — lo <= hi is a representation invariant and no \
|
|
longer sits behind --no-bounds-checks — so ASan is still silent \
|
|
here and now for a better reason. The trap itself is asserted in \
|
|
test_acceptance.ml" ]
|
|
in
|
|
match compile ~sanitize:true ~checks:false "programs/bounds.flan" with
|
|
| exception Failure m -> fail "unchecked bounds.flan: build: %s" m
|
|
| exe ->
|
|
List.iter
|
|
(fun a ->
|
|
let _, t = run exe [ a ] in
|
|
if not (reported t) then
|
|
fail "unchecked bounds.flan %s: nothing reported, and this is the \
|
|
case that says ASan sees an unchecked build at all\n%s" a t)
|
|
reports;
|
|
List.iter
|
|
(fun (a, why) ->
|
|
let _, t = run exe [ a ] in
|
|
if reported t then
|
|
Printf.printf
|
|
"note unchecked bounds.flan %s now reports; it did not, on the \
|
|
grounds that %s\n" a why
|
|
else
|
|
Printf.printf "note unchecked bounds.flan %s: silent — %s\n" a why)
|
|
silent;
|
|
(try Sys.remove exe with Sys_error _ -> ())
|
|
|
|
let () =
|
|
match Sys.command "command -v clang > /dev/null 2>&1" with
|
|
| 0 ->
|
|
(* A read one past the end of a four-element global. Index 5 and not 9,
|
|
and the difference is worth knowing: ASan registers this array as
|
|
"16 bytes in a 32-byte slot", so the poisoned redzone is bytes 16..31.
|
|
Index 5 is byte 20 and is caught; index 9 is byte 36, past the
|
|
registration entirely, and is silent. Overrunning a small object by
|
|
enough lands back in ordinary memory. *)
|
|
control ~expect_report:true "flan-san-ctl-oob"
|
|
~why:"This sweep is not instrumenting Flan code at all — check that \
|
|
Emit still puts every define in the sanitize_address attribute \
|
|
group, without which -fsanitize=address covers the runtime's C \
|
|
and nothing else."
|
|
"(defvar arr [4 i32])\n\
|
|
(defn main [] i32\n\
|
|
\ (set (at arr 0) 1)\n\
|
|
\ (let [i 5] (print (at arr i)) (println \"\"))\n\
|
|
\ 0)\n";
|
|
(* Shift by the full width of the type: undefined in C, poison in LLVM,
|
|
and invisible to UBSan here because nothing emitted a check for it. If
|
|
this ever starts reporting, the note above is stale. *)
|
|
control ~expect_report:false "flan-san-ctl-shift"
|
|
~why:"UBSan has started seeing Flan code, which contradicts what this \
|
|
file and Build.opts both say it reaches. Good news; rewrite them."
|
|
"(defn main [] i32\n\
|
|
\ (let [x 1] (let [n 32] (print (<< x n)) (println \"\")))\n\
|
|
\ 0)\n";
|
|
(* A regression case, and the one defect this exercise found: a slice's
|
|
length is signed, (slice s 2 1) is -1, and flan_bytes_to_i64 cast that
|
|
to size_t before comparing it against its buffer — so the memcpy copied
|
|
63 bytes out of whatever the slice pointed at. Every other (ptr, len)
|
|
entry point in the runtime already guarded the negative case; these two
|
|
were the exceptions. A checked build traps on the reversed slice long
|
|
before this, which is why it needs an unchecked build to show. *)
|
|
control ~expect_report:false ~args:[ "2" ] "flan-san-ctl-negslice"
|
|
~why:"flan_bytes_to_i64 or flan_bytes_to_f64 is reading off the end of \
|
|
a negative-length slice again — see clamp_len in flan_rt.c."
|
|
"(defn main [args [string]] i32\n\
|
|
\ (let [s (bytes \"42\")\n\
|
|
\ n (i32 (bytes->i64 (bytes (at args 1))))]\n\
|
|
\ (print (bytes->i64 (slice s n 1)))\n\
|
|
\ (println \"\"))\n\
|
|
\ 0)\n";
|
|
sweep ~checks:true "checked";
|
|
dyn_sweep ();
|
|
unchecked_controls ();
|
|
if !failures = 0 then print_endline "sanitizer sweep: clean"
|
|
else Printf.printf "%d sanitizer failure(s)\n" !failures;
|
|
exit (if !failures = 0 then 0 else 1)
|
|
| _ ->
|
|
print_endline "no clang on PATH; sanitizer sweep skipped"
|