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* Native support for bit fields (#400)Xavier Leroy2021-08-221-59/+102
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This big PR adds support for bit fields in structs and unions to the verified part of CompCert, namely the CompCert C and Clight languages. The compilation of bit field accesses to normal integer accesses + shifts and masks is done and proved correct as part of the Cshmgen pass. The layout of bit fields in memory is done by the functions in module Ctypes. It follows the ELF ABI layout algorithm. As a bonus, basic soundness properties of the layout are shown, such as "two different bit fields do not overlap" or "a bit field and a regular field do not overlap". All this replaces the previous emulation of bit fields by source-to-source rewriting in the unverified front-end of CompCert (module cparse/Bitfield.ml). This emulation was prone to errors (see nonstandard layout instead. The core idea for the PR is that expressions in l-value position denote not just a block, a byte offset and a type, but also a bitfield designator saying whether all the bits of the type are accessed (designator Full) or only some of its bits (designator Bits). Designators of the Bits kind appear when the l-value is a bit field access; the bit width and bit offset in Bits are computed by the functions in Ctypes that implement the layout algorithm. Consequently, both in the semantics of CompCert C and Clight and in the SimplExpr, SimplLocals and Cshmgen compilation passes, pairs of a type and a bitfield designator are used in a number of places where a single type was used before. The introduction of bit fields has a big impact on static initialization (module cfrontend/Initializers.v), which had to be rewritten in large part, along with its soundness proof (cfrontend/Initializersproof.v). Both static initialization and run-time manipulation of bit fields are tested in test/abi using differential testing against GCC and randomly-generated structs. This work exposed subtle interactions between bit fields and the volatile modifier. Currently, the volatile modifier is ignored when accessing a bit field (and a warning is printed at compile-time), just like it is ignored when accessing a struct or union as a r-value. Currently, the natural alignment of bit fields and their storage units cannot be modified with the aligned attribute. _Alignas on bit fields is rejected as per C11, and the packed modifier cannot be applied to a struct containing bit fields.
* SimplExpr: better translation of casts in a "for effects" contextXavier Leroy2020-06-151-55/+71
| | | | | | | | This is useful for statements such as `(void) expr;` where we would prefer not to explicitly compute intermediate values of type `void` and store them in Clight temporary variables. See issue #361 for a real-world occurrence of this phenomenon.
* Coq 8.10 compatibility: make explicit the "core" hint databaseXavier Leroy2019-08-051-1/+1
| | | | | "Hint Resolve foo." becomes "Hint Resolve foo : core", or "Local Hint Resolve foo : core".
* Early optimization of redundant *& and &* addressingsXavier Leroy2017-05-291-3/+3
| | | | | | Particularly annoying was the `*&x` sequence where `x` is a local variable, which would force stack-allocation of `x` early, generating extra loads and stores that could not always be optimized later (in CSE and Deadcode). The `*&` sequences and, by symmetry, the `&*` sequences are now eliminated early during Clight generation, via smart constructors.
* attempt to optimize empty if/then/else statementsMichael Schmidt2017-04-061-2/+5
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* Merge pull request #93 from AbsInt/separate-compilationXavier Leroy2016-03-201-41/+6
|\ | | | | | | | | | | | | | | | | | | | | | | This pull request implements "approach A" to separate compilation in CompCert from the paper Lightweight verification of separate compilation by Jeehoon Kang, Yoonseung Kim, Chung-Kil Hur, Derek Dreyer, Viktor Vafeiadis, POPL 2016, pages 178-190 In a nutshell, semantic preservation is still stated and proved in terms of a whole C program and a whole assembly program. However, the whole C program can be the result of syntactic linking of several C compilation units, each unit being separated compiled by CompCert to produce assembly unit, and these assembly units being linked together to produce the whole assembly program. This way, the statement of semantic preservation and its proof now take into account the fact that each compilation unit is compiled separately, knowing only a fragment of the whole program (i.e. the current compilation unit) rather than the whole program.
| * Update the proofs of the C front-end to the new linking framework.Xavier Leroy2016-03-061-41/+6
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* | Make casts of pointers to _Bool semantically well defined (again).Xavier Leroy2016-03-021-20/+9
|/ | | | | | In compCert 2.5 the semantics of pointer comparisons against the NULL pointer was made more accurate by making it undefined if the pointer is invalid (outside bounds). Technical difficulties prevented this change from being propagated to the semantics of casts from pointer types to the _Bool type, which involves an implicit pointer comparison against NULL. Hence, this kind of casts was temporarily given undefined semantics. This commit makes pointer-to-_Bool casts semantically defined (again), provided the pointer is valid. This reinstates the equivalence between casts to _Bool and comparisons != 0. The technical difficulties mentioned above came from the translation of assignments in a value context in the SimplExpr pass. The pass was lightly modified to work around the issue.
* Restart the name generator at first_unused_ident for every function.Xavier Leroy2016-02-051-15/+16
| | | | This makes it easier to generate semi-meaningful names for compiler-generated temporaries in the clightgen tool.
* Updated PR by removing whitespaces. Bug 17450.Bernhard Schommer2015-10-201-82/+82
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* Represent struct and union types by name instead of by structure.Xavier Leroy2014-12-221-2/+2
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* Revised translation of '&&' and '||' to Clight.Xavier Leroy2014-10-131-14/+14
| | | | | | | | | | | The previous translation (in SimplExpr) produced references to the same temporary variable with two different types (bool and int), which is not nice if we want to typecheck the generated Clight. The new translation avoids this and also gets rid of the double cast to bool then to int. The trick is to change Eparen (in CompCert C expressions) to take two types: the type to which the argument must be converted, and the type with which the resulting expression is seen.
* Merge of "newspilling" branch:xleroy2014-07-231-0/+4
| | | | | | | | | | | | | | | - Support single-precision floats as first-class values - Introduce chunks Many32, Many64 and types Tany32, Tany64 to support saving and restoring registers without knowing the exact types (int/single/float) of their contents, just their sizes. - Memory model: generalize the opaque encoding of pointers to apply to any value, not just pointers, if chunks Many32/Many64 are selected. - More properties of FP arithmetic proved. git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2537 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
* Simpler, more robust emulation of calls to variadic functions:xleroy2013-12-281-2/+3
| | | | | | | | | | | | | | - C function types and Cminor signatures annotated by calling conventions. esp. vararg / not vararg - Cshmgen: generate correct code for function call where there are more arguments than listed in the function prototype. This is still undefined behavior according to the formal semantics, but correct code is generated. - C2C, */PrintAsm.ml: remove "printf$iif" hack. - powerpc/, checklink/: don't generate stubs for variadic functions. git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2386 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
* Support "default" cases in the middle of a "switch", not just at the end.xleroy2013-12-211-5/+4
| | | | git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2383 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
* Merge of the "princeton" branch:xleroy2013-06-161-10/+60
| | | | | | | | | | | | | | - Define type "block" as "positive" instead of "Z". - Strengthen mem_unchanged_on so that the permissions are identical, instead of possibly increasing. - Move mem_unchanged_on from Events to Memory.Mem. - Define it in terms of mem_contents rather than in terms of Mem.load. - ExportClight: try to name temporaries introduced by SimplExpr - SimplExpr: avoid reusing temporaries between different functions, instead, thread a single generator through all functions. git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2276 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
* Issue with simplification of nested ?: expressions of different types.xleroy2013-05-191-52/+82
| | | | | | | | (Ill-typed Clight/Cminor/RTL code was generated due to incorrect reuse of destination temporary.) git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2257 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
* Big merge of the newregalloc-int64 branch. Lots of changes in two directions:xleroy2013-04-201-0/+4
| | | | | | | | | 1- new register allocator (+ live range splitting, spilling&reloading, etc) based on a posteriori validation using the Rideau-Leroy algorithm 2- support for 64-bit integer arithmetic (type "long long"). git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2200 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
* lib/Integers.v: revised and extended, faster implementation based onxleroy2013-02-101-1/+1
| | | | | | | | bit-level operations provided by ZArith in Coq 8.4. Other modules: adapted accordingly. git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2110 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
* Ported to Coq 8.4pl1. Merge of branches/coq-8.4.xleroy2013-01-291-106/+106
| | | | git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2101 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
* Remove some useless "Require".xleroy2012-12-301-2/+0
| | | | | | | Update ARM port. git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2085 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
* Merge of the clightgen branch:xleroy2012-12-291-1/+1
| | | | | | | | | | | | | | | | | | - Alternate semantics for Clight where function parameters are temporaries, not variables - New pass SimplLocals that turns non-addressed local variables into temporaries - Simplified Csharpminor, Cshmgen and Cminorgen accordingly - SimplExpr starts its temporaries above variable names, therefoe Cminorgen no longer needs to encode variable names and temps names. - Simplified Cminor parser & printer, as well as Errors, accordingly. - New tool clightgen to produce Clight AST in Coq-parsable .v files. - Removed side condition "return type is void" on rules skip_seq in the semantics of CompCert C, Clight, C#minor, Cminor. - Adapted RTLgenproof accordingly (now uses a memory extension). git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2083 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
* Make Clight independent of CompCert C.xleroy2012-10-081-0/+2
| | | | | | | Common parts are factored out in cfrontend/Ctypes.v and cfrontend/Cop.v git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2060 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
* Merge of branch seq-and-or. See Changelog for details.xleroy2012-10-061-120/+290
| | | | git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2059 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
* - Support for _Alignof(ty) operator from ISO C 2011xleroy2012-02-261-0/+7
| | | | | | | | | | and __alignof__(ty), __alignof__(expr) from GCC. - Resurrected __builtin_memcpy_aligned, useful for files generated by Scade KCG 6. git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@1827 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
* Translate CompCert C's "a ? b : c" to the equivalent simple Clight expr ifxleroy2012-02-251-3/+30
| | | | | | | b and c are simple. git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@1826 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
* Merge of the "volatile" branch:xleroy2012-02-041-27/+76
| | | | | | | | | | | | - native treatment of volatile accesses in CompCert C's semantics - translation of volatile accesses to built-ins in SimplExpr - native treatment of struct assignment and passing struct parameter by value - only passing struct result by value remains emulated - in cparser, remove emulations that are no longer used - added C99's type _Bool and used it to express || and && more efficiently. git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@1814 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
* In conditional expressions e1 ? e2 : e3, cast the results of e2 and e3 to ↵xleroy2011-07-161-22/+22
| | | | | | | | | the type of the whole conditional expression. Replaced predicates "cast", "is_true" and "is_false" by functions "sem_cast" and "bool_val". git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@1684 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
* Merge of branches/full-expr-4:xleroy2010-08-181-0/+815
- Csyntax, Csem: source C language has side-effects within expressions, performs implicit casts, and has nondeterministic reduction semantics for expressions - Cstrategy: deterministic red. sem. for the above - Clight: the previous source C language, with pure expressions. Added: temporary variables + implicit casts. - New pass SimplExpr to pull side-effects out of expressions (previously done in untrusted Caml code in cparser/) - Csharpminor: added temporary variables to match Clight. - Cminorgen: adapted, removed cast optimization (moved to back-end) - CastOptim: RTL-level optimization of casts - cparser: transformations Bitfields, StructByValue and StructAssign now work on non-simplified expressions - Added pretty-printers for several intermediate languages, and matching -dxxx command-line flags. git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@1467 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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