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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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- Make it possible to skip tests on some platforms
- Make it possible to expect a failure (typically: of the reference interpreter)
- Stop on error
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This commits adds code generation for the RISC-V architecture, both in 32- and 64-bit modes.
The generated code was lightly tested using the simulator and cross-binutils from https://riscv.org/software-tools/
This port required the following additional changes:
- Integers: More properties about shrx
- SelectOp: now provides smart constructors for mulhs and mulhu
- SelectDiv, 32-bit integer division and modulus: implement constant propagation, use the new smart constructors mulhs and mulhu.
- Runtime library: if no asm implementation is provided, run the reference C implementation through CompCert. Since CompCert rejects the definitions of names of special functions such as __i64_shl, the reference implementation now uses "i64_" names, e.g. "i64_shl", and a renaming "i64_ -> __i64_" is performed over the generated assembly file, before assembling and building the runtime library.
- test/: add SIMU make variable to run tests through a simulator
- test/regression/alignas.c: make sure _Alignas and _Alignof are not #define'd by C headers
commit da14495c01cf4f66a928c2feff5c53f09bde837f
Author: Xavier Leroy <xavier.leroy@inria.fr>
Date: Thu Apr 13 17:36:10 2017 +0200
RISC-V port, continued
Now working on Asmgen.
commit 36f36eb3a5abfbb8805960443d087b6a83e86005
Author: Xavier Leroy <xavier.leroy@inria.fr>
Date: Wed Apr 12 17:26:39 2017 +0200
RISC-V port, first steps
This port is based on Prashanth Mundkur's experimental RV32 port and brings it up to date with CompCert, and adds 64-bit support (RV64). Work in progress.
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-> x86/x86_32/x86_64
Having Archi.ptr64 as an opaque Parameter that is determined at run-time depending on compcert.ini is problematic for applications such as VST where functions such as Ctypes.sizeof must compute within Coq.
This commit introduces two versions of the Archi.v file, one for x86 32 bits (with ptr64 := false), one for x86 64 bits (with ptr64 := true). Unlike previous approaches, no other file is duplicated between these two variants of x86.
While we are at it, I renamed "ia32" into "x86" everywhere. "ia32" is Intel speak for the 32-bit architecture. It is not a good name to describe both the 32 and 64 bit architectures.
Finally, .depend is no longer under version control and is regenerated when the target architecture changes. That's because the location of Archi.v differs between the ports that have 32/64 bit variants (x86 so far) and the ports that have only one bitsize (ARM and PowerPC so far).
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Tests updated to work with x86 64 bits.
Infrastructure added: script "Runtest", with ability to have different reference outputs depending on platform or bit size.
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