1 | (* Type of values used in the dynamic semantics of the back-end intermediate |
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2 | languages. Inspired by common/Values.ma, adapted from Compcert *) |
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3 | |
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4 | include "common/Pointers.ma". |
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5 | |
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6 | record part (r: region): Type[0] ≝ |
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7 | { part_no:> nat |
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8 | ; part_no_ok: part_no ≤ size_pointer r |
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9 | }. |
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10 | |
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11 | (* Byte-sized values used in the back-end. |
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12 | Values larger than a single Byte are represented via their parts. |
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13 | Values are either: |
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14 | - machine integers (Bytes) |
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15 | - parts of a pointer seen as a triple giving the representation of the |
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16 | pointer (in terms of the memory regions such a pointer could address), |
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17 | a memory address and an integer offset with respect to this address; |
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18 | - a null pointer: the region denotes the pointer size |
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19 | - the [BVundef] value denoting an arbitrary bit pattern, such as the |
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20 | value of an uninitialized variable |
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21 | *) |
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22 | |
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23 | inductive beval: Type[0] ≝ |
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24 | | BVundef: beval |
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25 | | BVByte: Byte → beval |
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26 | | BVnull: ∀r:region. part r → beval |
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27 | | BVptr: ∀p:pointer. part (ptype p) → beval. |
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28 | |
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29 | definition eq_beval: beval → beval → bool ≝ |
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30 | λv1,v2. |
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31 | match v1 with |
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32 | [ BVundef ⇒ match v2 with [ BVundef ⇒ true | _ ⇒ false ] |
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33 | | BVByte b1 ⇒ match v2 with [ BVByte b2 ⇒ eq_bv … b1 b2 | _ ⇒ false ] |
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34 | | BVnull r1 p1 ⇒ match v2 with [ BVnull r2 p2 ⇒ eq_region … r1 r2 ∧ eqb p1 p2 | _ ⇒ false ] |
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35 | | BVptr P1 p1 ⇒ match v2 with [ BVptr P2 p2 ⇒ eq_pointer … P1 P2 ∧ eqb p1 p2 | _ ⇒ false ]]. |
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36 | |
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37 | axiom CorruptedValue: String. |
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38 | |
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39 | let rec pointer_of_bevals_aux (p:pointer) (part: nat) (l: list beval) on l : res pointer ≝ |
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40 | match l with |
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41 | [ nil ⇒ |
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42 | if eqb part (size_pointer (ptype p)) then |
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43 | OK … p |
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44 | else |
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45 | Error … [MSG CorruptedValue] |
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46 | | cons v tl ⇒ |
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47 | match v with |
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48 | [ BVptr p' part' ⇒ |
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49 | if eq_pointer p p' ∧ eqb part part' then |
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50 | pointer_of_bevals_aux p (S part) tl |
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51 | else |
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52 | Error … [MSG CorruptedValue] |
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53 | | _ ⇒ Error … [MSG CorruptedValue]]]. |
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54 | |
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55 | axiom NotAPointer: String. |
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56 | |
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57 | (* CSC: use vectors in place of lists? Or even better products of tuples |
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58 | (more easily pattern matchable in the finite case)? requires one more parameter *) |
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59 | definition pointer_of_bevals: list beval → res pointer ≝ |
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60 | λl. |
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61 | match l with |
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62 | [ nil ⇒ Error … [MSG NotAPointer] |
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63 | | cons he tl ⇒ |
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64 | match he with |
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65 | [ BVptr p part ⇒ |
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66 | if eqb part 0 then pointer_of_bevals_aux p 1 tl else Error … [MSG NotAPointer] |
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67 | | _ ⇒ Error … [MSG NotAPointer]]]. |
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68 | |
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69 | (* CSC: use vectors in place of lists? Or even better products of tuples |
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70 | (more easily pattern matchable in the finite case)? *) |
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71 | let rec bevals_of_pointer_aux (p:pointer) (part: nat) (n: nat) (pr: plus part n = size_pointer (ptype p)) on n: list beval ≝ |
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72 | match n with |
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73 | [ O ⇒ λ_.[] |
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74 | | S m ⇒ λpr':n=S m.(BVptr p (mk_part … part …))::bevals_of_pointer_aux p (S part) m ?] (refl ? n). |
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75 | /3/ qed. |
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76 | |
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77 | definition bevals_of_pointer: pointer → list beval ≝ |
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78 | λp. bevals_of_pointer_aux p 0 (size_pointer (ptype p)) …. |
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79 | // qed. |
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80 | |
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81 | lemma pointer_of_bevals_bevals_of_pointer: |
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82 | ∀p. pointer_of_bevals (bevals_of_pointer p) = OK … p. |
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83 | * * #pbl #pok #poff |
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84 | try % |
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85 | whd in ⊢ (??%?) >reflexive_eq_pointer >(eqb_n_n 1) [2,3: %] |
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86 | whd in ⊢ (??%?) >reflexive_eq_pointer >(eqb_n_n 2) % |
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87 | qed. |
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88 | |
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89 | (* CSC: move elsewhere *) |
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90 | (* CSC: Wrong data-type? Use products of products *) |
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91 | definition list_to_pair: ∀A:Type[0]. ∀l:list A. length … l = 2 → A × A. |
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92 | #A #l cases l [2: #a #tl cases tl [2: #b #tl' cases tl' [1: #_ @〈a,b〉 | #c #tl'']]] |
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93 | #abs normalize in abs; destruct |
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94 | qed. |
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95 | |
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96 | axiom NotATwoBytesPointer: String. |
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97 | |
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98 | (* Fails if the address is not representable as a pair *) |
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99 | definition beval_pair_of_pointer: pointer → res (beval × beval) ≝ |
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100 | λp. match p with [ mk_pointer pty pbl pok poff ⇒ |
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101 | match pty with |
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102 | [ XData ⇒ λpok. OK … (list_to_pair … (bevals_of_pointer (mk_pointer XData pbl pok poff)) ?) |
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103 | | Code ⇒ λpok. OK … (list_to_pair … (bevals_of_pointer (mk_pointer Code pbl pok poff)) ?) |
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104 | | _ ⇒ λ_. Error … [MSG NotATwoBytesPointer]] pok]. |
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105 | % qed. |
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106 | |
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107 | axiom ValueNotABoolean: String. |
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108 | |
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109 | definition bool_of_beval: beval → res bool ≝ |
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110 | λv.match v with |
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111 | [ BVundef ⇒ Error … [MSG ValueNotABoolean] |
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112 | | BVByte b ⇒ OK … (eq_bv … (zero …) b) |
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113 | | BVnull x y ⇒ OK … false |
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114 | | BVptr p q ⇒ OK ? true ]. |
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115 | |
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116 | axiom BadByte: String. |
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117 | |
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118 | definition Byte_of_val: beval → res Byte ≝ (*CSC: move elsewhere *) |
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119 | λb.match b with |
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120 | [ BVByte b ⇒ OK … b |
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121 | | _ ⇒ Error … [MSG BadByte]]. |
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122 | |
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123 | (* CSC: maybe we should introduce a type of 1-bit-sized values *) |
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124 | definition BVtrue: beval ≝ BVByte [[false;false;false;false;false;false;false;true]]. |
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125 | definition BVfalse: beval ≝ BVByte (zero …). |
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126 | definition beval_of_bool : bool → beval ≝ λb. if b then BVtrue else BVfalse. |
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