| Commit message (Collapse) | Author | Age | Files | Lines |
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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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Casting from an integer constant to pointer on 64 bit
architectures did not take the signedness into account and always
interpreted the integer as unsigned which causes some
incompatibility with libc implementations.
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"Hint Resolve foo." becomes "Hint Resolve foo : core", or
"Local Hint Resolve foo : core".
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It is type-checked like a conditional expression then translated to
a call to the known builtin function.
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During the experiments, the integer + pointer cases was removed from the semantics of the C addition operator. The idea was to turn integer + pointer into pointer + integer during elaboration, but it was not implemented.
On second thoughts, we can restore the integer + pointer cases in the formal semantics of CompCert C at low cost. This is what this commit does.
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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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Make casts of pointers to _Bool semantically well defined
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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.
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Support <pointer> +/- <integer> where the pointer value is actually an integer (Vint) that has been converted to pointer type.
Such arithmetic, while not defined in ISO C, appears in the wild. If present in static initializers, it used to cause a compile-time failure ("not a compile-time constant"). Hence this relaxation.
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Val.lessdef, etc.
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It used to be that a pointer value (Vptr) always compare unequal to the
null pointer (Vint Int.zero). However, this may not be true in the
final machine code when pointer addition overflows and wraps around
to the bit pattern 0. This patch checks the validity of the pointer
being compared with 0, and makes the comparison undefined if the
pointer is out of bounds.
Note: only the IA32 back-end was updated, ARM and PowerPC need updating.
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(in CompCert C to Cminor, included)
- Translation of "switch" to decision trees or jumptables made generic
over the sizes of integers and moved to the Cminor->CminorSel pass
instead of CminorSel->RTL as before.
- CminorSel: add "exitexpr" to support the above.
- ValueDomain: more precise analysis of comparisons against an integer
literal. E.g. "x >=u 0" is always true.
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2565 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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- 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
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- Ctypes: add useful functions on attributes; remove attrs in typeconv
(because attributes are meaningless on r-values)
- C2C: fixed missing or redundant Evalof
- Cop: ignore attributes in ptr + int and ptr - int (meaningless on r-values);
add sanity check between typeconv/classify_binarith and the C99 standard.
- cparser: fixed several cases where incorrect type annotations were put
on expressions.
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2457 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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for Epostincr operations.
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2455 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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More precise classification of float results of arithmetic operations,
in preparation for future work on the C/Clight static type system.
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2441 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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- 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
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enabling more aggressive optimizations.
- Less aggressive CSE for EF_builtin builtins, causes problems
for __builtin_write{16,32}_reversed.
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2363 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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- introduce Float.floatofint{,u} and use it in the semantics of C
- prove that it is equivalent to int->double conversion followed by
double->float rounding, and use this fact to justify code generation
in Cshmgen.
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2294 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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casts int64 -> float64 -> float32. The latter causes double rounding
errors.
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2290 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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- 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
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"the usual binary conversions" and be more robust towards future extensions
e.g. with 32-bit float values.
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2239 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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test/c: added SHA3
cfrontend: support casts between long long and pointers, and comparisons between them.
git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2213 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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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
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git-svn-id: https://yquem.inria.fr/compcert/svn/compcert/trunk@2118 fca1b0fc-160b-0410-b1d3-a4f43f01ea2e
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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
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