| 1 | Status of matita port of CompCert 1.6 C semantics |
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| 2 | ================================================= |
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| 3 | |
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| 4 | Last seen working with matita svn r10890. |
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| 5 | |
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| 6 | - Most of the memory model has been ported (common/Mem.v -> Mem.ma). |
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| 7 | The main exception is minor arithmetic results than were proven with |
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| 8 | omega, which we hope to prove using matita's automation at some |
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| 9 | point. |
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| 10 | |
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| 11 | - The memory model is executable; some small tests can be found in |
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| 12 | test/memorymodel.ma. Note that the handling of integer values is |
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| 13 | axiomatised, so conversions are not yet evaluated. |
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| 14 | |
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| 15 | - The C syntax has been ported, minus a few lemmas that are not used by |
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| 16 | the semantics. |
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| 17 | |
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| 18 | - Most of the small-step C semantics has been ported, although much of the |
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| 19 | underlying arithmetic and environment functions are only present as axioms, |
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| 20 | including the type of identifiers. |
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| 21 | |
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| 22 | - Nonetheless, this is sufficient to show the semantics of a trivial C program |
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| 23 | in test/trivial.ma. |
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| 24 | |
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| 25 | - A collection of definitions and lemmas that probably ought to be in |
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| 26 | matita's standard library can be found in extralib.ma. |
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| 27 | |
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| 28 | - Some of the machine integers (i.e., integers modulo) results are |
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| 29 | given as axioms in Integers.ma. Implementing them should be routine now that |
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| 30 | we have a binary representation of integers. The CompCert version is given |
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| 31 | as a functor on the word size - we don't have an equivalent of this yet. |
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| 32 | |
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| 33 | * Some experimental work on an executable semantics has been started in |
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| 34 | Cexec.ma. At present only a small subset of expressions and statements |
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| 35 | are handled. |
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| 36 | |
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| 37 | * The patch in compcert-1.7.1-matita.patch adds a -dmatita option to |
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| 38 | output a matita file containing a definition for the C program. |
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| 39 | Note that there must be a "main" function. (This was made against |
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| 40 | 1.7.1 for convenience - the Clight syntax is the same as 1.6.) |
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| 41 | |
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| 42 | There is a more recent version of compcert available with a revised memory |
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| 43 | model that may be more closely suited to our needs. |
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| 44 | |
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| 45 | matita issues and workarounds |
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| 46 | ----------------------------- |
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| 47 | |
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| 48 | No unfold tactic yet; use reduction or rewriting instead. |
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| 49 | |
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| 50 | Normalization of term containing large definitions (such as some of the |
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| 51 | Integers library) can be prohibitive. This is a particular problem because |
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| 52 | ndestruct currently normalizes the goal and every hypothesis that is rewritten. |
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| 53 | For ndestruct, getting rid of irrelevant information (e.g., replacing the goal |
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| 54 | with False) sometimes helps, an extra lemma can be used, or the definitions |
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| 55 | can make careful use of 'nlet rec' to prevent reduction. |
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| 56 | |
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| 57 | Some of the pattern matching in the C syntax has had to be unfolded in |
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| 58 | a rather unpleasant way (where matching on pairs was used in the original). |
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| 59 | |
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| 60 | The use of records in place of modules is a little delicate: large records |
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| 61 | tend to use a lot of memory and processor at the moment, and the names of the |
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| 62 | fields tend to clash a lot. |
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| 63 | |
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| 64 | The lack of sections has been replaced by duplicating the variables in some |
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| 65 | places, and adding a record in others. |
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| 66 | |
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| 67 | The meminj_no_overlap definition in Mem.ma uses the logical Or explicitly |
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| 68 | rather than the ∨ notation to regain reasonable performance. (This is |
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| 69 | presumably due to disambiguation - the notation is also used for booleans.) |
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| 70 | |
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| 71 | There are a couple of places in Mem.ma where rewriting had to be done carefully |
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| 72 | to avoid assertions during unification; I'm not really sure what the problem |
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| 73 | is. |
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| 74 | |
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| 75 | Detail per-file |
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| 76 | --------------- |
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| 77 | |
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| 78 | AST.ma |
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| 79 | |
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| 80 | Program transformation sections left alone. |
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| 81 | |
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| 82 | Coqlib.ma |
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| 83 | |
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| 84 | Only essential parts: |
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| 85 | - align |
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| 86 | - some 2^n lemmas (which could go into the binary libraries) |
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| 87 | - option_map |
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| 88 | - parts of list disjointness and non-repetition |
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| 89 | |
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| 90 | Csem.ma |
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| 91 | |
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| 92 | The small step semantics have been ported. None of the big step semantics or |
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| 93 | the equivalence proof has been ported. |
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| 94 | |
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| 95 | Csyntax.ma |
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| 96 | |
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| 97 | Everything except for a few minor definitions / lemmas that are not required |
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| 98 | by the semantics. |
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| 99 | |
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| 100 | Errors.ma |
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| 101 | |
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| 102 | Only a basic definition without error messages. |
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| 103 | |
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| 104 | Events.ma |
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| 105 | |
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| 106 | Most of the definitions; haven't needed many of the lemmas yet. |
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| 107 | |
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| 108 | Floats.ma |
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| 109 | |
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| 110 | Axiomatised, but so was the original! |
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| 111 | |
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| 112 | Globalenvs.ma |
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| 113 | |
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| 114 | Basic definition only. |
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| 115 | |
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| 116 | Integers.ma |
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| 117 | |
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| 118 | Most of the operations have been ported, although some have been left as |
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| 119 | axioms because the underlying operation is not present. The use of the |
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| 120 | Coq module system to abstract over the word size has been left out for |
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| 121 | now. |
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| 122 | |
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| 123 | Maps.ma |
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| 124 | |
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| 125 | Only a basic definition. |
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| 126 | |
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| 127 | Mem.ma |
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| 128 | |
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| 129 | Everything except for omega in proofs. |
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| 130 | |
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| 131 | Smallstep.ma |
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| 132 | |
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| 133 | Ported definitions for multiple steps and program behaviour; left |
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| 134 | alternative definitions, some lemmas, plus simulations sections for later. |
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| 135 | |
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| 136 | Values.ma |
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| 137 | |
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| 138 | The definitions about values which don't rely on arithmetics operations that |
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| 139 | haven't been ported yet are done. The other definitions and most of the |
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| 140 | lemmas still remain to be done. |
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| 141 | |
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| 142 | |
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