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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.
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The GPL makes sense for whole applications, but the dual-licensed Coq
and OCaml files are more like libraries to be combined with other
code, so the LGPL is more appropriate.
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Move its definitions to modules C (the type `builtins`) and Env
(the operations that deal with the initial environment).
Reasons for the refactoring:
1- The name "Builtins" will soon be reused for a Coq module
2- `Env.initial()` makes more sense than `Builtins.environment()`.
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Instead of relying testing that the size of pointers is 64bit the
size of registers should be tested. Also it should be a fatal
error to reverse a long long on an architecture that does not
support reverse 64bit read/writes.
Bug 24982
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CompCert has two implementations of sizeof, alignof and offsetof (byte offset of a struct field):
- the reference implementation, in Coq, from cfrontend/Ctypes.v
- the implementation used during elaboration, in OCaml, from cparser/Cutil.ml
The reference Coq implementation is used as much as possible, but sometimes during elaboration the size of a type must be computed (e.g. to compute array sizes), or the offset of a field (e.g. to evaluate __builtin_offsetof), in which case the OCaml implementation is used.
This causes issues with packed structs. Currently, the cparser/Cutil.ml functions ignore the "packed" attribute on structs. Their results disagree with the "true" sizes, alignments and offsets computed by the cfrontend/Ctypes.v functions after source-to-source transformation of packed structs as done in cparser/PackedStruct.ml. For example:
```
struct __packed__(1) s { char c; short s; int i; };
assert (__builtin_offsetof(struct s, i) == 3);
assert (sizeof(struct s) = sizeof(char[sizeof(struct s)]));
```
The two assertions fail. In the first assertion, __builtin_offsetof is elaborated to 4, because the packed attribute is ignored during elaboration. In the second assertion, the type `char[sizeof(struct s)]` is elaborated to `char[8]`, again because the packed attribute is ignored during elaboration, while the other `sizeof(struct s)` is computed as 7 after the source-to-source transformation of packed structs.
This commit changes the cparser/Cutil.ml functions so that they take the packed attribute into account when computing sizeof, alignof, offsetof, and struct_layout.
Related changes:
* cparser/Cutil: add `packing_parameters` function to extract packing info from attributes
* cparser/Cutil: refactor and share more code between sizeof_struct, offsetof, and struct_layout
* cparser/Elab: check the alignment parameters given in packed attributes. (The check was previously done in cparser/PackedStruct.ml but now it would come too late.)
* cparser/Elab: refactor the checking of alignment parameters between _Alignas, attribute((aligned)), __packed__, and attribute((packed)).
* cparser/PackedStructs: simplify the code, some functionality was moved to cparser/Cutil, other to cparser/Elab
* cfrontend/C2C: raise an "unsupported" error if a packed struct is defined and -fpacked-structs is not given. Before, the packed attribute would be silently ignored, but now doing so would cause inconsistencies between cfrontend/ and cparser/.
* test/regression/packedstruct1.c: add tests to compare the sizes and the offsets produced by the elaborator with those obtained after elaboration.
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* Module Cerrors is now called Diagnostic and can be used in parts of CompCert other than cparser/
* Replaced eprintf error. Instead of having eprintf msg; exit 2 use the functions from the
Diagnostics module.
* Raise on error before calling external tools.
* Added diagnostics to clightgen.
* Fix error handling of AsmToJson.
* Cleanup error handling of Elab and C2C.
*The implementation of location printing (file & line) is simplified and correctly prints valid filenames with invalid lines.
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- Introduce Archi.ptr64 parameter.
- Define module Ptrofs of integers as wide as a pointer (64 if Archi.ptr64, 32 otherwise).
- Use Ptrofs.int as the offset type for Vptr values and anywhere pointer offsets are manipulated.
- Modify Val operations that handle pointers (e.g. Val.add, Val.sub, Val.cmpu) so that in 64-bit pointer mode it is the "long" operation (e.g. Val.addl, Val.subl, Val.cmplu) that handles pointers.
- Update the memory model accordingly.
- Modify C operations that handle pointers (e.g. addition, subtraction, comparisons) accordingly.
- Make it possible to turn off the splitting of 64-bit integers into pairs of 32-bit integers.
- Update the compiler front-end and back-end accordingly.
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Now each warning either has a name and can be turned on/off, made
into an error,etc. or is a warning that always will be triggered.
The message of the warnings are similar to the ones emited by
gcc/clang and all fit into one line.
Furthermore the diagnostics are now colored if colored output is
available.
Bug 18004
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The code was mostly there for documentation effort. So warning
27 is deactivated again.
Bug 18349
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Removed some unused variables, functions etc. and resolved some
problems which occur if all warnings except 3,4,9 and 29 are active.
Bug 18394.
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Use tail-recursive operations to implement transformations on initializers for global arrays. This way, very large static initializers no longer cause stack overflows at compile-time.
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Bitfields: better translation of initializers and compound literals; run this pass before unblocking.
Transform.stmt: extend with ability to treat unblocked code.
test/regression: more bitfield tests.
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Several definitions in Cutil and elsewhere were accessing the default
value of !Machine.config, before it is properly initialized in Driver.
Delay evaluation of these definitions, and initialize Machine.config
to nonsensical values so that lack of initialization is caught early
(e.g. in Cutil.find_matching_*_kind).
Also, following up on commit [3b8a094], don't use "wchar_t" typedef
to type wide string literals, even if this typedef is in scope.
The risk here is to hide an inconsistency between "wchar_t"'s definition
in standard headers and CompCert's built-in definition.
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We now distinguish 3 modes (instead of 2 previously) for attributes: 1- strict compatibility, 2- ignore top-level attrs, 3- ignore all attrs recursively.
In strict mode, const/volatile/restrict attributes must be identical, but nonstandard attributes may vary.
Also: ignore top-level attrs when comparing function argument types, like GCC/Clang do.
Net result is fewer warnings and type-checking that is closer to GCC/Clang.
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git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2615 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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PackedStructs.ml: remove "packed" attribute once processed.
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2388 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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Ceval.ml: tolerate non-zero integers with pointer types.
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2343 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2342 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2291 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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for compatibility with earlier CompCert versions.
But don't use them in PackedStructs.
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2216 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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Remove __builtin_{read,write}_reversed from IA32 and ARM ports.
Machregs: tighten destroyed_by_builtin
Packedstructs: use bswap if read/write-reversed not available.
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2208 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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cparser: add primitive support for enum types.
bitfield emulation: for bitfields with enum type, choose signed/unsigned as appropriate
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2074 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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cparser: renamed Errors to Cerrors; removed packing into Cparser.
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@1856 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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PackedStructs: honor 'aligned' attribute on packed struct fields
C2C: warn for ignored 'aligned' attributes
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@1837 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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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
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cparser/PackedStructs: treat r-m-w operations over byte-swapped fields
cparser/PackedStructs: allow static initialization of packed structs
test/regression: more packedstruct tests
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@1738 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@1730 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@1729 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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Elsewhere: refactoring, moving common code into Cutil and Transform
(to be continued)
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@1716 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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cparser: added experimental emulation of packed structs (PackedStruct.ml)
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@1650 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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