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The datatype package of HOL4 does not support the prompt monad, so this patch
restores the option to generate a model that only uses the state monad. Also
add a Makefile target cheri_sequential.lem in the cheri/ directory.
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mono rewrites
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Also clean up some library functions a bit, and add some missing failure
handling variants of division operations on bitvectors.
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They are used in various specs and test cases.
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(note that they're already declared in lib/arith.sail)
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Rename l2.ott to sail.ott
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definitions from sail/lib.
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In particular, improve indentation of if-expressions, and provide infix syntax
for monadic binds in Isabelle, allowing Lem to preserve source whitespace.
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- Update Lem bindings and extras files
- Rewrite Nexp_var's if they are bound to a constant, similar to Nexp_id's
(used for cap_size in the CHERI spec)
- Add Lem and Isabelle Makefile targets for CHERI
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Some functions are partial, e.g. converting a bitvector to an integer, which
might fail for the bit list representation due to undefined bits. Undefined
cases can be handled in different ways:
- call Lem's failwith, which maps to undefined/ARB in Isabelle and HOL (the
default so far),
- return an option type,
- raise a failure in the monad, or
- use a bitstream oracle to resolve undefined bits.
This patch adds different versions of partial functions corresponding to those
options. The desired behaviour can be selected by choosing a binding in the
Sail prelude. The naming scheme is that the failwith version is the default,
while the other versions have the suffixes _maybe, _fail, and _oracle,
respectively.
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The state monad currently assumes that tags are written to and read from
properly aligned addresses (since it does not know the capability size used in
the Sail model). This change allows the Sail model to pass in the aligned
address(es) even if data is written to an unaligned address. There might be
better ways to model tag writing, but this approach seems rather general.
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This simplifies reasoning in Isabelle.
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Currently ignored in the state monad
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Add an Undefined outcome to the prompt monad that asks the environment for a
Boolean value. For the state monad, add fields for a random generator and a
seed (currently of type nat) to the state.
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Rather than just using strings to represent literals, now use value
types from sail_lib.lem to represent them. This allows for expressions
to be evaluated at compile time, which will be useful for future
optimisations involving constant folding and propagation, and allows
the intermediate bytecode to be interpreted using the same lem
builtins that the shallow embedding uses.
To get this to work I had to tweak the build process slightly to allow
ml files to import lem files from gen_lib/. Hopefully this doesn't
break anything!
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The suffix _lemmas is more descriptive than _extras.
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Architecture-specific lemmas about concrete registers and types are generated
and written to a file <prefix>_lemmas.thy, generic lemmas are in the
theories *_extras.thy in lib/isabelle. In particular, State_extras contains
simplification lemmas about the lifting from prompt to state monad.
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Generate only one Lem model based on the prompt monad (instead of two models
with different monads), and add a lifting from prompt to state monad. Add some
Isabelle lemmas about the monad lifting.
Also drop the "_embed" and "_sequential" suffixes from names of generated
files.
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- Use simplified monad type (e.g., without the with_aux constructors that are
not needed by the shallow embedding).
- Add support for registers with arbitrary types (e.g., records, enumerations,
vectors of vectors). Instead of using bit lists as the common representation
of register values at the monad interface, use a register_value type that is
generated per spec as a union of all register types that occur in the spec.
Conversion functions between register_value and concrete types are generated.
- Use the same representation of register references as the state monad, in
preparation of rebasing the state monad onto the prompt monad.
- Split out those types from sail_impl_base.lem that are used by the shallow
embedding into a new module sail_instr_kinds.lem, and import that. Removing
the dependency on Sail_impl_base from the shallow embedding avoids name clashes
between the different monad types.
Not yet done:
- Support for reading/writing register slices. Currently, a rewriting pass
pushes register slices in l-expressions to the right-hand side, turning a
write to a register slice into a read-modify-write. For interfacing with the
concurreny model, we will want to be more precise than that (in particular
since some specs represent register files as big single registers containing a
vector of bitvectors).
- Lemmas about the conversion functions to/from register_value should be
generated automatically.
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removed IK_cond_branch, and added IK_branch
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passing tests.
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(accidentally committed the wrong file)
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Makes bitvector typeclass instance dictionaries disappear from generated
Isabelle output.
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combinators)
Add Isabelle-specific theories imported directly after monad definitions, but
before other combinators. These theories contain lemmas that tell the function
package how to deal with monadic binds in function definitions.
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The internal function _reg_deref is declared as pure, so that bitfield setters
can be implemented as read-modify-write, while only having a wreg effect.
However, for the Lem shallow embedding, the read step of those setters needs to
be embedded into the monad. This could be special-cased in the Lem pretty
printer, but then the pretty printer would have to replicate some logic of the
letbind_effects rewriting step. It seems simplest to add the effect annotation
early in the Lem rewriting pipeline, in the fix_val_specs step. This means
that this rewriting step can only be used for other backends if these
additional effects are acceptable.
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- Remove vector start indices
- Library refactoring: Definitions in sail_operators.lem now use Bitvector
type class and work for both bit list and machine word representations
- Add Lem bindings to AArch64 and RISC-V preludes
TODO: Merge specialised machine word operations from sail_operators_mwords into
sail_operators.
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The type-checker already supports a user-defined "exception" type that can be
used in throw and try-catch expressions. This patch adds support for that to
the Lem shallow embedding by adapting the existing exception mechanisms of the
state and prompt monads. User-defined exceptions are distinguished from
builtin exception cases. For example, the state monad uses
type ex 'e =
| Exit
| Assert of string
| Throw of 'e
to distinguish between calls to "exit", failed assertions, and user-defined
exceptions, respectively. Early return is also handled using the exception
mechanism, by lifting to a monad with "either 'r exception" as the exception
type, where 'r is the expected return type and "exception" is the user-defined
exception type.
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- Add support for some internal nodes to type checker
- Add more explicit type annotations during rewriting
- Remove hardcoded rewrites for E_vector_update etc from Lem pretty-printer;
these will be resolved by the type checker during rewriting now
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Also, rename a few functions for uniformity, e.g. bool_and -> and_bool
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