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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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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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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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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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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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- 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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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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- 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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Map to calls to monadic function assert_exp that throws an exception if the
assertion is false
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- Remove start indices and indexing order from bitvector types. Instead add
them as arguments to functions accessing/updating bitvectors. These arguments
are effectively implicit, thanks to wrappers in prelude_wrappers.sail and a
"sizeof" rewriting pass.
- Add a typeclass for bitvectors with a few basic functions (converting to/from
bitlists, converting to an integer, getting and setting bits). Make both
monads use this interface, so that they work with both the bitlist and the
machine word representation of bitvectors.
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- Add back support for bit list representation of bit vectors, for backwards
compatibility in order to ease integration with the interpreter. For this
purpose, split out a file sail_operators.lem from sail_values.lem, and add a
variant sail_operators_mwords.lem for the machine word representation of
bitvectors. Currently, Sail is hardcoded to use machine words for the
sequential state monad, and bit lists for the free monad, but this could be
turned into a command line flag.
- Add a prelude_wrappers.sail file for glueing the Sail prelude to the Lem
library. The wrappers make use of sizeof expressions to extract type
information from bitvectors (length, start index) in order to pass it to the
Lem functions.
- Add early return support to the free monad, using a new constructor "Return
of 'r". As with the sequential monad, functions with early return are
wrapped into "catch_early_return", which extracts the return value at the end
of the function execution.
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- Add case distinctions between bitvector types and vectors of other element
types (e.g. registers) and use the corresponding operations (i.e. "bvslice",
"bvaccess", etc for the former, and "slice", "access", etc for the latter) when
pretty-printing expressions
- Add type annotations to expressions when the type includes bitvectors with
concretely known length
- Update state.lem to use bitvectors (in the interface, at least; internally,
bitvectors are still stored as bit lists for now, since that makes it easier
to support storing different registers with different lengths)
This has been tested with the CHERI-MIPS model with some success, but some
things are still missing:
- Bitvector patterns are not handled yet
- Some bitvector length monomorphisation is needed in a few places of the model
- Some type annotations are missing, because the (old) Sail type checker does
not infer bitvector lengths in some instances where one would hope it to do
that; this should be checked with the new type checker
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instruction state, factor out interpreter/shallow embedding value conversion
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state monad, library fixes
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letbound variables
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sail_impl_base, add sail_impl_base.outcome, add interp_inter_imp auxiliary functions, make prompt use sail_impl_base.outcome
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for-loops or case-expressions also return updated variables
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{power,armv8}_extras.lem; fixes
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