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Fix examples after en tree #1827
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Original file line number | Diff line number | Diff line change |
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@@ -685,54 +685,60 @@ Open a new coq file `tutorial_c_proofs.v` in the same folder | |
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``` | ||
From CryptolToCoq Require Import SAWCoreScaffolding. | ||
From CryptolToCoq Require Import SAWCoreScaffolding. | ||
From CryptolToCoq Require Import SAWCoreVectorsAsCoqVectors. | ||
From CryptolToCoq Require Import SAWCoreBitvectors. | ||
From CryptolToCoq Require Import SAWCorePrelude. | ||
From CryptolToCoq Require Import CompMExtra. | ||
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(* The following line enables pretty printing*) | ||
Import CompMExtraNotation. Open Scope fun_syntax. | ||
(* The following 2 lines allows better automation *) | ||
Require Import Examples.common. | ||
Require Import Coq.Program.Tactics. (* Great tacticals, move to automation. Perhaps `Require Export`? *) | ||
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(* Import our function definitions*) | ||
Require Import Examples.tutorial_c_gen. | ||
Import tutorial_c. | ||
``` | ||
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It first imports all the SAW functionality we need and enables pretty | ||
printing. Then it imports our new definitions (e.g. `add`). | ||
It first imports all the SAW functionality we need and some useful | ||
tactics. Then it imports our new definitions (e.g. `add`). | ||
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Our first proof will claim that the function `add` produces no | ||
errors. More specifically, it says that for all inputs (that's what | ||
`refinesFun` quantifies) `add` always refines to `noErrorsSpec`. That | ||
is, it returns a pure value. | ||
`spec_refines_eq` quantifies) `add` always refines to `safety_spec`. That | ||
is, it returns a pure value without errors. | ||
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``` | ||
Lemma no_errors_add | ||
: refinesFun add (fun _ _ => noErrorsSpec). | ||
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Lemma no_errors_add (x y: bitvector 64) : | ||
spec_refines_eq (add x y) (safety_spec (x,y)). | ||
Proof. | ||
``` | ||
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We will use our automation to quickly prove the lemma, but we must | ||
first unfold those definitions the the automation is unfamiliar with. | ||
We will use our automation to quickly prove the lemma, | ||
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``` | ||
unfold add, add__tuple_fun, noErrorsSpec. | ||
solve_trivial_spec 0 0. Qed. | ||
``` | ||
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Then our function `prove_refinement` will deal with the proof. | ||
You can also attempt the same proof with `add_mistyped`, which | ||
obviously will fail, since `add_mistyped` has an error. First, you | ||
will note that `add_mistyped` only takes one argument (since only one | ||
was defined in its signature) | ||
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``` | ||
prove_refinement. | ||
Qed. | ||
Lemma no_errors_add_mistyped (x: bitvector 64) : | ||
spec_refines_eq (add_mistyped x) (safety_spec (x)). | ||
Proof. solve_trivial_spec 0 0. | ||
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clarify_goal_tutorial. | ||
``` | ||
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You can also attempt the same proof with `add_mistyped`, which | ||
obviously will fail, since `add_mistyped` has an error. | ||
After rewriting the terms for clarity, you can see the | ||
remaining goal says that an `ErrorS` is a refinement of | ||
`RetS`. In other words, it's trying to prove that a trivially | ||
pure function has an error. That's obviously false. | ||
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``` | ||
Lemma no_errors_add_mistyped | ||
: refinesFun add_mistyped (fun _ => noErrorsSpec). | ||
Proof. | ||
unfold add_mistyped, add_mistyped__tuple_fun, noErrorsSpec. | ||
prove_refinement. | ||
(* Fails to solve the goal. *) | ||
Abort. | ||
``` | ||
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@@ -793,12 +799,9 @@ You will have to generate the `.vo` again to write proofs about | |
produces no errors. | ||
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``` | ||
Lemma no_errors_incr_ptr | ||
: refinesFun incr_ptr (fun _ => noErrorsSpec). | ||
Proof. | ||
unfold incr_ptr, incr_ptr__tuple_fun. | ||
prove_refinement. | ||
Qed. | ||
Lemma no_errors_incr_ptr (x: bitvector 64) : | ||
spec_refines_eq (incr_ptr x) (safety_spec x). | ||
Proof. solve_trivial_spec 0 0. Qed. | ||
``` | ||
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### Structs | ||
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@@ -963,64 +966,56 @@ adds dynamic checks on the extracted code which we will see in the Coq | |
code. | ||
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Let's go to `arrays_gen.v` (which has already been generated for you) | ||
and look for the definition of `zero_array__tuple_fun`. You will | ||
notice that it calls `errorM` twice but, in this case that's not a | ||
and look for the definition of `zero_array__bodies`. You will | ||
notice that it calls `errorS` twice, but in this case, that's not a | ||
sign of a typing error! Heapster includes these errors to catch | ||
out-of-bounds array accesses and unrepresentable indices (i.e. index | ||
that can't be written as a machine integer). The code below is a | ||
simplification of the `zero_array__tuple_fun` with some notation for | ||
simplification of the `zero_array__bodies` with some notation for | ||
readability (see below for how to enable such pritty printing). | ||
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``` | ||
zero_array__tuple_fun = | ||
(* ... Some ommited code ... *) | ||
LetRec f:= | ||
(fun (e1 e2 : int64) (p1 : Vector int64 e1) | ||
(_ _ _ : unit : Type) => | ||
(* ... Some ommited code ... *) | ||
let var__4 := (0)[1] in | ||
let var__6 := e2 < e1 in | ||
(*... Some ommited code ...*) | ||
if | ||
not | ||
((if var__6 then 1 else var__4) == | ||
var__4) | ||
then | ||
if | ||
((17293822569102704640)[64] <= e2) && | ||
(e2 <= (1152921504606846975)[64]) | ||
then | ||
If e2 <P e1 | ||
Then f e1 (e2 + (1)[64]) | ||
(p1 [e2 <- (0)[64]]) tt tt tt | ||
Else errorM "ghost_bv <u top_bv" | ||
else | ||
errorM "Failed Assert at arrays.c:61:5" | ||
else returnM p1, tt) | ||
InBody (f e0 (0)[64] p0 tt tt tt), tt)) | ||
(fun (e0 : int64) (p0 : Vector int64 e0) => | ||
CallS VoidEv emptyFunStack zero_array__frame | ||
(mkFrameCall zero_array__frame 1 e0 (0)[64] p0 tt tt tt), | ||
(fun (e0 e1 : int64) (p0 : Vector int64 e0) (_ _ _ : unit) => | ||
if negb ((if e1 < e0 then (-1)[1] else (0)[1]) == (0)[1]) | ||
then | ||
if ((17293822569102704640)[64] <= e1) && (e1 <= (1152921504606846975)[64]) | ||
then | ||
If e1 <P e0 | ||
Then CallS VoidEv emptyFunStack zero_array__frame | ||
(mkFrameCall zero_array__frame 1 e0 (e1 + (1)[64]) | ||
(p0 [e1 <- (0)[64]]) tt tt tt) | ||
Else ErrorS (Vector int64 e0) "ghost_bv <u top_bv" | ||
else ErrorS (Vector int64 e0) "Failed Assert at arrays.c:61:5" | ||
else RetS p0, tt)) | ||
``` | ||
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The arguments `e1`, `e2` and `p1` correspond to the length `len`, the | ||
Notice there are two functions, the outermost one represents | ||
`zero_array` and the one inside represents the loop. in the latter, | ||
the arguments `e0`, `e1` and `p1` correspond to the length `len`, the | ||
offset `i`, and the array `arr`. Notice most of that the function | ||
performs several tests before executing any computation. The first two | ||
tests, which are within `if then else` blocks, check that the offset | ||
is less than the array length `e2 < e1`, and that the index `i` is | ||
is less than the array length `e1 < e0`, and that the index `i` is | ||
within the bounds of machine integers. The former is part of the loop | ||
condition, the second is added by Heapster to ensure the ghost | ||
variable represents a machine integer. | ||
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The last check, which is within uppercase `If Then Else` (which | ||
handles option types) is not part of the original function but | ||
inserted by Heapster. It checks that the array access is within bounds | ||
`e2 <P e1`. The operator `<P` returns an optional proof of the array | ||
`e1 <P e0`. The operator `<P` returns an optional proof of the array | ||
access being safe. If the check fails, the function reports a runtime | ||
error `errorM "ghost_bv <u top_bv"`. | ||
error `ErrorS _ "ghost_bv <u top_bv"`. | ||
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If all the checks pass, then the function simply calls | ||
itself recursively, with the next index and array with a new entry zeroed out. | ||
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``` | ||
f e1 (e2 + (1)[64]) (p1 [e2 <- (0)[64]]) tt tt tt | ||
(mkFrameCall zero_array__frame 1 e0 (e1 + (1)[64]) | ||
(p0 [e1 <- (0)[64]]) tt tt tt) | ||
``` | ||
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The extra `tt` are artifacts that get inserted by Heapster, but you | ||
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@@ -1040,9 +1035,10 @@ We shall now prove that this function in fact should never return an | |
error if the inputs are correct. Go to `array_proofs.v` and look at the proof | ||
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``` | ||
Lemma no_errors_zero_array | ||
: refinesFun zero_array (fun x _ => assumingM (zero_array_precond x) noErrorsSpec). | ||
Proof | ||
Lemma no_errors_zero_array x y: | ||
spec_refines_eq (zero_array x y) | ||
(total_spec (fun '(len, vec, dec) => zero_array_precond len) (fun _ _ => True) (x,y, bvAdd _ x (intToBv _ 1))). | ||
Proof. | ||
``` | ||
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It claims that, assuming the precondition `zero_array_precond` is | ||
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@@ -1057,12 +1053,10 @@ Definition zero_array_precond x | |
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We will not go into detail about the proof, but notice that the | ||
important steps are handled by custom automation. Namely we use the | ||
commands `prove_refinement_match_letRecM_l` and `prove_refinement` to | ||
handle refinements with and without recursion (respectively). The rest | ||
of the proof, consists of discharging simple inequalities and a couple | ||
of trivial entailments, where the left hand side is an error (and thus | ||
entails anything). | ||
important steps are handled by custom automation. | ||
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TODO: This proof is involved. Perhaps add some more details? | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Yes, I definitely think so! Are you planning to resolve this TODO in this PR, or are you leaving this as future work? There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. It's a good point. The description more or less gets to the limit of what I understand, without going into technical details. Do you have any suggestion of how to improve this section? We can also just commit the comment and leave it super high level at this point. There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Ideally, we would include a more detailed tutorial that goes into the nuances of
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### Recursive data structures | ||
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Original file line number | Diff line number | Diff line change |
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@@ -6,11 +6,11 @@ | |
linked_list_gen.v | ||
linked_list_proofs.v | ||
xor_swap_gen.v | ||
#xor_swap_proofs.v | ||
xor_swap_proofs.v | ||
xor_swap_rust_gen.v | ||
#xor_swap_rust_proofs.v | ||
c_data_gen.v | ||
#c_data_proofs.v | ||
c_data_proofs.v | ||
Comment on lines
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to
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There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. I'm surprised that this isn't adding back more of the There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. I haven't finished the proofs in |
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string_set_gen.v | ||
#string_set_proofs.v | ||
loops_gen.v | ||
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@@ -39,3 +39,4 @@ sha512_gen.v | |
#sha512_proofs.v | ||
io_gen.v | ||
#io_proofs.v | ||
common.v |
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I'm not sure how to read this comment. Does this belong in a tutorial?
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I guess not.