Stricter indexing for bitvector types. Previous versions of Sail
treated bitvector('n) as uninhabited if 'n < 0, but otherwise
permitted such bitvector types in signatures. Now the type
bitvector('n) is only well-formed if 'n >= 0. This is a breaking
change, as some previously permitted definitions are now rejected
without additional constraints. However Sail has a new kind Nat
which allows it to infer these >= 0 constraints when explicit type
variables are ommited, so in a function signature
val foo : forall 'n. bits('n) -> bool
the 'n type variable will be inferred as:
val foo : forall ('n : Nat). bits('n) -> bool
This release mostly incorporates many small improvements and fixes to Sail 0.17.1.
This release introduces a simple module system. See the section of the manual for details.
If expressions are now permitted in types, so one can write types such as
bits(if XLEN == 32 then 15 else 57)
this doesn't add any additional expressiveness, as one could previously introduce additional type variables and constrain them in such a way to guarantee the same thing, but being able to use if-then-else directly is usually more clear.
Previously, type synonyms would require annotation with kinds (types of types), for example:
union option('a : Type) = { Some : 'a, None : unit }
type xlen : Int = 64
Now, type variable kinds are inferred in most places, so the above could be written as:
union option('a) = { Some : 'a, None : unit }
type xlen = 64
There are still some places where explicit kinds are necessary, such as for scattered type definitions or abstract types.
The Sail documentation backend can now produce hyperlinked and syntax
highlighted source code output with the --html option. The
Asciidoctor plugin can now hyperlink between definitions included in
the documentation, and otherwise link into a hyperlinked version of
the source.
Updated 0.17 release with bugfixes for:
- Issue 362 #362
Additionally includes patches for better ASL to Sail compatibility
This release is primarily intended to fix performance issues. Overall the Sail to C compilation can be almost 10x faster, and consumes significantly less memory.
The order parameter on the bitvector and vector types no longer does
anything. The default Order <ord> statement now sets the bitvector
and vector ordering globally. In practice only POWER uses increasing
bit order, and there is never a valid reason to mix them in a
specification. Overall they added significant complexity to the
language for no real gain. Over subsequent releases a warning will be
added before they are eventually removed from the syntax.
For a while string append patterns x ^ y have been marked with a
special non-executable effect that forbids them from being used. Now
the implementation has been removed due to the deleterious effect
the generated code has on performance. Such clauses are now eagerly
removed from the syntax tree during rewriting pending a revised
implementation.
Sail can now produce SystemVerilog output using the -sv flag. Note that this is not intended to be human readable or produce a synthesizable design, but is instead intended to be used with SystemVerilog verification tools like JasperGold.
A new documentation backend for integrating with Asciidoctor has been added.
The sail -fmt option can be used to automatically format Sail
source. This currently misses some features and can produce ugly
output in some known cases, so is not ready for serious usage yet.
Various bugfixes including:
Various mapping issues such as:
- Issue 244: #244
As well as other minor issues
The val cast syntax and support for implict casts is now entirely
removed, as mentioned in the previous release changes. The flags are
still allowed (to avoid breaking Makefiles) but no longer do anything.
The pattern completeness checker has been improved and is now context sensitive in some cases.
The Sail internals have been refactored into separate packages for each Sail backend (c/lem/coq and so on). The shared parts of Sail are now contained in a separate libsail OCaml library. The main Sail executable links together all the Sail backends into a single executable.
With this architecture new backends can be implemented outside the
main Sail repository as plugins, and loaded via sail -plugin.
The Sail build system has been transitioned from the legacy ocamlbuild system to dune.
This has been a significant refactoring of the core Sail codebase, and while all efforts have been taken to ensure backwards-compatibility and minimise any potential breakage, it is possible there exists some.
Sail now has a new pattern completeness checker that can generate counterexamples for incomplete patterns. It is designed to be less noisy, as it only issues warnings when it can guarantee that the pattern is incomplete.
Previously they were only forbidden by the -dno_cast flag (which is
used by both sail-riscv and sail-arm). This behaviour is now the
default and this flag is ignored. The -allow_deprecated_casts flag
must be used to enable this now. Implicit casts will be fully removed
in the next Sail release.
This release contains a new way of interfacing with external
concurrency models by way of user defined effects. See
lib/concurrency_interface for an example. This is currently
experimental and not fully supported in all backends. Definition of
new effects is currently only allowed with the $sail_internal
directive (see below).
Explicit effect annotations are now deprecated and do nothing. This change relates to the previous change to allow custom outcomes in the event monad, as the effect system no-longer corresponded in any meaningful way with whether functions would become monadic or not in Sail's theorem prover backends.
Function specifications (val keyword) can now be marked as pure. If
this is done, the functions must have no side-effects. The
requirements for a function to be pure in this sense are stricter than
they were previously - a pure function must not:
- Throw an exception
- Exit (either explicitly or by failing an assertion)
- Contain a possibly incomplete pattern match
- Read or write any register
- Call any impure function
This more strict notion of purity fixes some long-standing bugs when generating theorem prover definitions from Sail.
Note that functions do not have to be explicitly marked pure to be considered pure. Purity will be inferred automatically. The pure annotation is used to declare primitive functions as pure, and make it a hard error if a function is inferred to be impure.
There are two places in the language where code must be pure:
- Top level let-bindings
let x = exp - Loop and function termination measures
Previously Sail allowed some assignment constructions that were a bit complex, for example one could declare a variable and modify an existing one in the same statement, e.g.
x: int = 1;
(x, y: int) = (2, 3);
This is now forbidden, so l-expressions can either modify existing variables or declare new ones, but never both simultaneously. This change is primarily to increase readability, and simplify the language internally.
In the future we may move further towards a world where new
assignments must be declared with a var keyword, like the let
keyword.
Variable declarations are now forbidden in places where their scope is not syntactically obvious, for example:
val f : (unit, int) -> unit
...
f(x: int = 3, x)
The breakage caused by this change should be minor as we hope well-written Sail specifications do not declare variables in this way.
Error messages are now formatted as per:
https://www.gnu.org/prep/standards/standards.html#Errors
which should allow better editor integration
A new directive $sail_internal has been introduced. When placed in a
file this allows the use of experimental or unstable functionality. It
also allows the use of various identifiers that are ordinarily
forbidden. Its primary purpose is to allow the Sail library to be
implemented using new unstable features that may change, without them
being exposed (and therefore relied upon) by downstream users.
As such, any Sail file using this directive may become broken at any point.
This is mostly a bugfix release
Supports creating C code that works as a library in a more natural
way. Rather than defining lots of global state, the model state will
be packaged into a sail_state struct that is passed into each
generated C function. The code generation is much more configurable,
including options for fine-grained control over name-mangling (see
etc/default_config.json).
Currently the -c2 option can be used. Eventually it is planned that this will become the default C code generation option, and the old C code generator will be removed.
The monomorphisation pass for Isabelle and HOL4 has been improved significantly.
There is now a code coverage tool (sailcov) in the sailcov subdirectory of this repository
Can now define type synonyms for kinds other than Type. For example:
type xlen : Int = 64
type xlenbits = bits(xlen)
the syntax is
type <name> : <kind> = <value>
for synonyms with no arguments and
type <name>(<arguments>)[, <constraint>] -> <kind> = <value>
for synonyms that take arguments. Valid kinds are Int, Bool, Ord, and
Type. : Type or -> Type can be omitted.
This can be used to define constraint synonyms, e.g.
type is_register_index('n : Int) = 0 <= 'n <= 31
val my_function : forall 'n, is_register_index('n). int('n) -> ...
Type synonyms with constraints and multiple arguments can be declared as e.g.
type my_type('n: Int, 'm: Int), 'n > 'm > 0 = vector('n, dec, bits('m))
The previous syntax for numeric constants (which was never fully implemented) of
constant x = <value>
is no longer supported.
Can now use C-c C-s in Emacs to start a Sail interactive
sub-process, assuming sail is available in $PATH. Using C-c C-l
or simply saving a changed Sail file will cause it to be checked. Type
errors will be highlighted within the Emacs buffer, and can be jumped
to using C-c C-x, much like Merlin for OCaml. C-c C-c will display
the type of the expression under the cursor for a checked Sail
file. This particular is slightly experimental and won't always
display the most precise type, although Emacs will bold the region
that sail thinks is under the cursor to make this clear. The
interactive Sail session can be ended using C-c C-q.
To support multiple file ISA specifications, a JSON file called sail.json can be placed in the same directory as the .sail files. It specifies the dependency order for the .sail files and any options required by Sail itself. As an example, the file for v8.5 is
{
"options" : "-non_lexical_flow -no_lexp_bounds_check",
"files" : [
"prelude.sail",
"no_devices.sail",
"aarch_types.sail",
"aarch_mem.sail",
"aarch64.sail",
"aarch64_float.sail",
"aarch64_vector.sail",
"aarch32.sail",
"aarch_decode.sail"
]
}For this to work Sail must be build with interactive support as make isail. This requires the yojson library as a new dependency (opam install yojson).
We now support Boolean type arguments in much the same way as numeric type arguments. Much like the type int('n), which means an integer equal to the type variable 'n, bool('p) now means a Boolean that is true provided the constraint 'p holds. This enables us to do flow typing in a less ad-hoc way, as we can now have types like
val operator <= : forall 'n 'm. (int('n), int('n)) -> bool('n <= 'm)
The main use case for this feature in specifications is to support flags that change the range of type variables, e.g:
val my_op : forall 'n ('f : Bool), 0 <= 'n < 15 & ('f | 'n < 4).
(bool('f), int('n)) -> unit
function my_op(flag, index) = {
if flag then {
// 0 <= 'n < 15 holds
let x = 0xF[index]; // will fail to typecheck here
...
} else {
// 0 <= 'n < 4 holds
let x = 0xF[index]; // will typecheck here
...
}
}
This change is mostly backwards compatible, except in some cases extra type annotations may be required when declaring mutable Boolean variables, so
x = true // declaration of x
x = false // type error because x inferred to have type bool(true)
should become
x : bool = true // declaration of x
x = false // fine because x can have any Boolean value
Function implicit arguments are now given explicitly in their type signatures so
val zero_extend : forall 'n 'm, 'm >= 'n. bits('n) -> bits('m)
function zero_extend(v) = zeros('m - length(v)) @ v
would now become
val zero_extend : forall 'n 'm, 'm >= 'n. (implicit('m), bits('n)) -> bits('m)
function zero_extend(m, v) = zeros(m - length(v)) @ v
This radically simplifies how we resolve such implicit arguments during type-checking, and speeds up processing large specifications like ARM v8.5 significantly.
There is a symbol FEATURE_IMPLICITS which can be used with $ifdef
to write both new and old-versions if desired for backwards
compatibility, as the new version is syntactically valid in older Sails,
but just doesn't typecheck.
Bitfields can now be parameterised in the following way:
type xlenbits = bits(xlen)
bitfield Mstatus : xlenbits = {
SD : xlen - ylen,
SXL : xlen - ylen - 1 .. xlen - ylen - 3
}
This bitfield would then be valid for either
type xlen : Int = 64
type ylen : Int = 1
or
type xlen : Int = 32
type ylen : Int = 1
The monad embedding for Lem has been changed to make it more friendly for theorem proving. This can break model-specific Lem that depends on the definitions in src/gen_lib.