WebAssembly memory operations are by definition little-endian even on
big-endian target platforms. However, other memory accesses will require
native target endianness (e.g. to access parts of the VMContext that is
also accessed by VM native code). This means on big-endian targets,
the code generator will have to handle both little- and big-endian
memory accesses. However, there is currently no way to encode that
distinction into the Cranelift IR that describes memory accesses.
This patch provides such a way by adding an (optional) explicit
endianness marker to an instance of MemFlags. Since each Cranelift IR
instruction that describes memory accesses already has an instance of
MemFlags attached, this can now be used to provide endianness
information.
Note that by default, memory accesses will continue to use the native
target ISA endianness. To override this to specify an explicit
endianness, a MemFlags value that was built using the set_endianness
routine must be used. This patch does so for accesses that implement
WebAssembly memory operations.
This patch addresses issue #2124.
There has been some confusion over the meaning of the "sign-extend"
(`sext`) and "zero-extend" (`uext`) attributes on parameters and return
values in signatures. According to the three implemented backends, these
attributes indicate that a value narrower than a full register should
always be extended in the way specified. However, they are much more
useful if they mean "extend in this way if the ABI requires extending":
only the ABI backend knows whether or not a particular ABI (e.g., x64
SysV vs. x64 Baldrdash) requires extensions, while only the frontend
(CLIF generator) knows whether or not a value is signed, so the two have
to work in concert.
This is the result of some very helpful discussion in #2354 (thanks to
@uweigand for raising the issue and @bjorn3 for helping to reason about
it).
This change respects the extension attributes in the above way, rather
than unconditionally extending, to avoid potential performance
degradation as we introduce more extension attributes on signatures.
* Rewrite interpreter generically
This change re-implements the Cranelift interpreter to use generic values; this makes it possible to do abstract interpretation of Cranelift instructions. In doing so, the interpretation state is extracted from the `Interpreter` structure and is accessed via a `State` trait; this makes it possible to not only more clearly observe the interpreter's state but also to interpret using a dummy state (e.g. `ImmutableRegisterState`). This addition made it possible to implement more of the Cranelift instructions (~70%, ignoring the x86-specific instructions).
* Replace macros with closures
As discussed in #2251, in order to be very confident that NaN signaling bits are correctly handled by the compiler, this switches `DataValue` to use Cranelift's `Ieee32` and `Ieee64` structures. This makes it a bit more inconvenient to interpreter Cranelift FP operations but this should change to something like `rustc_apfloat` in the future.
This change abstracts away (from the perspective of the new backend) how immediate values are stored in InstructionData. It gathers large immediates from necessary places (e.g. constant pool) and delegates to `InstructionData::imm_value` for the rest. This refactor only touches original users of `LowerCtx::get_immediate` but a future change could do the same for any place the new backend is accessing InstructionData directly to retrieve immediates.
As part of a Wasm JIT update, SpiderMonkey is changing its internal
WebAssembly function ABI. The new ABI's frame format includes "caller
TLS" and "callee TLS" slots. The details of where these come from are
not important; from Cranelift's point of view, the only relevant
requirement is that we have two on-stack args that are always present
(offsetting other on-stack args), and that we define special argument
purposes so that we can supply values for these slots.
Note that this adds a *new* ABI (a variant of the Baldrdash ABI) because
we do not want to tightly couple the landing of this PR to the landing
of the changes in SpiderMonkey; it's better if both the old and new
behavior remain available in Cranelift, so SpiderMonkey can continue to
vendor Cranelift even if it does not land (or backs out) the ABI change.
Furthermore, note that this needs to be a Cranelift-level change (i.e.
cannot be done purely from the translator environment implementation)
because the special TLS arguments must always go on the stack, which
would not otherwise happen with the usual argument-placement logic; and
there is no primitive to push a value directly in CLIF code (the notion
of a stack frame is a lower-level concept).
The implementation is pretty straightforward. Wasm atomic instructions fall
into 5 groups
* atomic read-modify-write
* atomic compare-and-swap
* atomic loads
* atomic stores
* fences
and the implementation mirrors that structure, at both the CLIF and AArch64
levels.
At the CLIF level, there are five new instructions, one for each group. Some
comments about these:
* for those that take addresses (all except fences), the address is contained
entirely in a single `Value`; there is no offset field as there is with
normal loads and stores. Wasm atomics require alignment checks, and
removing the offset makes implementation of those checks a bit simpler.
* atomic loads and stores get their own instructions, rather than reusing the
existing load and store instructions, for two reasons:
- per above comment, makes alignment checking simpler
- reuse of existing loads and stores would require extension of `MemFlags`
to indicate atomicity, which sounds semantically unclean. For example,
then *any* instruction carrying `MemFlags` could be marked as atomic, even
in cases where it is meaningless or ambiguous.
* I tried to specify, in comments, the behaviour of these instructions as
tightly as I could. Unfortunately there is no way (per my limited CLIF
knowledge) to enforce the constraint that they may only be used on I8, I16,
I32 and I64 types, and in particular not on floating point or vector types.
The translation from Wasm to CLIF, in `code_translator.rs` is unremarkable.
At the AArch64 level, there are also five new instructions, one for each
group. All of them except `::Fence` contain multiple real machine
instructions. Atomic r-m-w and atomic c-a-s are emitted as the usual
load-linked store-conditional loops, guarded at both ends by memory fences.
Atomic loads and stores are emitted as a load preceded by a fence, and a store
followed by a fence, respectively. The amount of fencing may be overkill, but
it reflects exactly what the SM Wasm baseline compiler for AArch64 does.
One reason to implement r-m-w and c-a-s as a single insn which is expanded
only at emission time is that we must be very careful what instructions we
allow in between the load-linked and store-conditional. In particular, we
cannot allow *any* extra memory transactions in there, since -- particularly
on low-end hardware -- that might cause the transaction to fail, hence
deadlocking the generated code. That implies that we can't present the LL/SC
loop to the register allocator as its constituent instructions, since it might
insert spills anywhere. Hence we must present it as a single indivisible
unit, as we do here. It also has the benefit of reducing the total amount of
work the RA has to do.
The only other notable feature of the r-m-w and c-a-s translations into
AArch64 code, is that they both need a scratch register internally. Rather
than faking one up by claiming, in `get_regs` that it modifies an extra
scratch register, and having to have a dummy initialisation of it, these new
instructions (`::LLSC` and `::CAS`) simply use fixed registers in the range
x24-x28. We rely on the RA's ability to coalesce V<-->R copies to make the
cost of the resulting extra copies zero or almost zero. x24-x28 are chosen so
as to be call-clobbered, hence their use is less likely to interfere with long
live ranges that span calls.
One subtlety regarding the use of completely fixed input and output registers
is that we must be careful how the surrounding copy from/to of the arg/result
registers is done. In particular, it is not safe to simply emit copies in
some arbitrary order if one of the arg registers is a real reg. For that
reason, the arguments are first moved into virtual regs if they are not
already there, using a new method `<LowerCtx for Lower>::ensure_in_vreg`.
Again, we rely on coalescing to turn them into no-ops in the common case.
There is also a ridealong fix for the AArch64 lowering case for
`Opcode::Trapif | Opcode::Trapff`, which removes a bug in which two trap insns
in a row were generated.
In the patch as submitted there are 6 "FIXME JRS" comments, which mark things
which I believe to be correct, but for which I would appreciate a second
opinion. Unless otherwise directed, I will remove them for the final commit
but leave the associated code/comments unchanged.
* Refactor where results of compilation are stored
This commit refactors the internals of compilation in Wasmtime to change
where results of individual function compilation are stored. Previously
compilation resulted in many maps being returned, and compilation
results generally held all these maps together. This commit instead
switches this to have all metadata stored in a `CompiledFunction`
instead of having a separate map for each item that can be stored.
The motivation for this is primarily to help out with future
module-linking-related PRs. What exactly "module level" is depends on
how we interpret modules and how many modules are in play, so it's a bit
easier for operations in wasmtime to work at the function level where
possible. This means that we don't have to pass around multiple
different maps and a function index, but instead just one map or just
one entry representing a compiled function.
Additionally this change updates where the parallelism of compilation
happens, pushing it into `wasmtime-jit` instead of `wasmtime-environ`.
This is another goal where `wasmtime-jit` will have more knowledge about
module-level pieces with module linking in play. User-facing-wise this
should be the same in terms of parallel compilation, though.
The ultimate goal of this refactoring is to make it easier for the
results of compilation to actually be a set of wasm modules. This means
we won't be able to have a map-per-metadata where the primary key is the
function index, because there will be many modules within one "object
file".
* Don't clear out fields, just don't store them
Persist a smaller set of fields in `CompilationArtifacts` instead of
trying to clear fields out and dynamically not accessing them.
This lets us avoid the cost of `cranelift_codegen::ir::Opcode` to
`peepmatic_runtime::Operator` conversion overhead, and paves the way for
allowing Peepmatic to support non-clif optimizations (e.g. vcode optimizations).
Rather than defining our own `peepmatic::Operator` type like we used to, now the
whole `peepmatic` crate is effectively generic over a `TOperator` type
parameter. For the Cranelift integration, we use `cranelift_codegen::ir::Opcode`
as the concrete type for our `TOperator` type parameter. For testing, we also
define a `TestOperator` type, so that we can test Peepmatic code without
building all of Cranelift, and we can keep them somewhat isolated from each
other.
The methods that `peepmatic::Operator` had are now translated into trait bounds
on the `TOperator` type. These traits need to be shared between all of
`peepmatic`, `peepmatic-runtime`, and `cranelift-codegen`'s Peepmatic
integration. Therefore, these new traits live in a new crate:
`peepmatic-traits`. This crate acts as a header file of sorts for shared
trait/type/macro definitions.
Additionally, the `peepmatic-runtime` crate no longer depends on the
`peepmatic-macro` procedural macro crate, which should lead to faster build
times for Cranelift when it is using pre-built peephole optimizers.
Certain operations (e.g. widening) will have operands with types like `NxM` but will return results with types like `(N*2)x(M/2)` (double the lane width, halve the number of lanes; maintain the same number of vector bits). This is equivalent to applying two `DerivedFunction`s to the type: `DerivedFunction::DoubleWidth` then `DerivedFunction::HalfVector`. Since there is no easy way to apply multiple `DerivedFunction`s (e.g. most of the logic is one-level deep, 1d5a678124/cranelift/codegen/meta/src/gen_inst.rs (L618-L621)), I added `DerivedFunction::MergeLanes` to do the necessary type conversion.
* Switch CI back to nightly channel
I think all upstream issues are now fixed so we should be good to switch
back to nightly from our previously pinned version.
* Fix doc warnings
These instructions have fast, inline JIT paths for the common cases, and only
call out to host VM functions for the slow paths. This required some changes to
`cranelift-wasm`'s `FuncEnvironment`: instead of taking a `FuncCursor` to insert
an instruction sequence within the current basic block,
`FuncEnvironment::translate_table_{get,set}` now take a `&mut FunctionBuilder`
so that they can create whole new basic blocks. This is necessary for
implementing GC read/write barriers that involve branching (e.g. checking for
null, or whether a store buffer is at capacity).
Furthermore, it required that the `load`, `load_complex`, and `store`
instructions handle loading and storing through an `r{32,64}` rather than just
`i{32,64}` addresses. This involved making `r{32,64}` types acceptable
instantiations of the `iAddr` type variable, plus a few new instruction
encodings.
Part of #929
Also add configuration to CI to fail doc generation if any links are
broken. Unfortunately we can't blanket deny all warnings in rustdoc
since some are unconditional warnings, but for now this is hopefully
good enough.
Closes#1947
When we vendor Cranelift into Firefox, we need to be able to build with
the Firefox CI setup (unless we carry patches on top of upstream).
Unfortunately, the Firefox CI currently appears to build with a slightly
older version of Rust: I can't work out which version exactly, but one
without stable support for `matches!()`.
A recent attempt to version-bump Cranelift failed with build errors at
the two locations in this patch:
https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=305994046&repo=autoland&lineNumber=24829
I also see a bunch of uses of `matches!()` in Peepmatic, but those
crates are not built by Firefox, so we can leave them be for now, I
think.
These libcalls are useful for 32-bit platforms.
On x86_32 in particular, commit 4ec16fa0 added support for legalizing
64-bit shifts through SIMD operations. However, that legalization
requires SIMD to be enabled and SSE 4.1 to be supported, which is not
acceptable as a hard requirement.
This ports all of the identity, no-op, simplification, and canonicalization
related optimizations over from being hand-coded to the `peepmatic` DSL. This
does not handle the branch-to-branch optimizations or most of the
divide-by-constant optimizations.
* Remove Cranelift's OutOfBounds trap, which is no longer used.
* Change proc_exit to unwind instead of exit the host process.
This implements the semantics in https://github.com/WebAssembly/WASI/pull/235.
Fixes#783.
Fixes#993.
* Fix exit-status tests on Windows.
* Revert the wiggle changes and re-introduce the wasi-common implementations.
* Move `wasi_proc_exit` into the wasmtime-wasi crate.
* Revert the spec_testsuite change.
* Remove the old proc_exit implementations.
* Make `TrapReason` an implementation detail.
* Allow exit status 2 on Windows too.
* Fix a documentation link.
* Really fix a documentation link.
Previously, every call was lowered on AArch64 to a `call` instruction, which
takes a signed 26-bit PC-relative offset. Including the 2-bit left shift, this
gives a range of +/- 128 MB. Longer-distance offsets would cause an impossible
relocation record to be emitted (or rather, a record that a more sophisticated
linker would fix up by inserting a shim/veneer).
This commit adds a notion of "relocation distance" in the MachInst backends,
and provides this information for every call target and symbol reference. The
intent is that backends on architectures like AArch64, where there are different
offset sizes / addressing strategies to choose from, can either emit a regular
call or a load-64-bit-constant / call-indirect sequence, as necessary. This
avoids the need to implement complex linking behavior.
The MachInst driver code provides this information based on the "colocated" bit
in the CLIF symbol references, which appears to have been designed for this
purpose, or at least a similar one. Combined with the `use_colocated_libcalls`
setting, this allows client code to ensure that library calls can link to
library code at any location in the address space.
Separately, the `simplejit` example did not handle `Arm64Call`; rather than doing
so, it appears all that is necessary to get its tests to pass is to set the
`use_colocated_libcalls` flag to false, to make use of the above change. This
fixes the `libcall_function` unit-test in this crate.
Certain operations (e.g. x86_packss) will have operands with types like `NxM` but will return results with types like `(N/2)x(M*2)` (halve the lane width, double the number of lanes; maintain the same number of vector bits). This is equivalent to applying two `DerivedFunction`s to the type: `DerivedFunction::HalfWidth` then `DerivedFunction::DoubleVector`. Since there is no easy way to apply multiple `DerivedFunction`s (e.g. most of the logic is one-level deep, 1d5a678124/cranelift/codegen/meta/src/gen_inst.rs (L618-L621)), I added `DerivedFunction::SplitLanes` to do the necessary type conversion.
* Implement interrupting wasm code, reimplement stack overflow
This commit is a relatively large change for wasmtime with two main
goals:
* Primarily this enables interrupting executing wasm code with a trap,
preventing infinite loops in wasm code. Note that resumption of the
wasm code is not a goal of this commit.
* Additionally this commit reimplements how we handle stack overflow to
ensure that host functions always have a reasonable amount of stack to
run on. This fixes an issue where we might longjmp out of a host
function, skipping destructors.
Lots of various odds and ends end up falling out in this commit once the
two goals above were implemented. The strategy for implementing this was
also lifted from Spidermonkey and existing functionality inside of
Cranelift. I've tried to write up thorough documentation of how this all
works in `crates/environ/src/cranelift.rs` where gnarly-ish bits are.
A brief summary of how this works is that each function and each loop
header now checks to see if they're interrupted. Interrupts and the
stack overflow check are actually folded into one now, where function
headers check to see if they've run out of stack and the sentinel value
used to indicate an interrupt, checked in loop headers, tricks functions
into thinking they're out of stack. An interrupt is basically just
writing a value to a location which is read by JIT code.
When interrupts are delivered and what triggers them has been left up to
embedders of the `wasmtime` crate. The `wasmtime::Store` type has a
method to acquire an `InterruptHandle`, where `InterruptHandle` is a
`Send` and `Sync` type which can travel to other threads (or perhaps
even a signal handler) to get notified from. It's intended that this
provides a good degree of flexibility when interrupting wasm code. Note
though that this does have a large caveat where interrupts don't work
when you're interrupting host code, so if you've got a host import
blocking for a long time an interrupt won't actually be received until
the wasm starts running again.
Some fallout included from this change is:
* Unix signal handlers are no longer registered with `SA_ONSTACK`.
Instead they run on the native stack the thread was already using.
This is possible since stack overflow isn't handled by hitting the
guard page, but rather it's explicitly checked for in wasm now. Native
stack overflow will continue to abort the process as usual.
* Unix sigaltstack management is now no longer necessary since we don't
use it any more.
* Windows no longer has any need to reset guard pages since we no longer
try to recover from faults on guard pages.
* On all targets probestack intrinsics are disabled since we use a
different mechanism for catching stack overflow.
* The C API has been updated with interrupts handles. An example has
also been added which shows off how to interrupt a module.
Closes#139Closes#860Closes#900
* Update comment about magical interrupt value
* Store stack limit as a global value, not a closure
* Run rustfmt
* Handle review comments
* Add a comment about SA_ONSTACK
* Use `usize` for type of `INTERRUPTED`
* Parse human-readable durations
* Bring back sigaltstack handling
Allows libstd to print out stack overflow on failure still.
* Add parsing and emission of stack limit-via-preamble
* Fix new example for new apis
* Fix host segfault test in release mode
* Fix new doc example
This allows us to give names to constants in the constant pool and then use these names in the function body. The original behavior, specifiying the constant value as an instruction immediate, is still supported as a shortcut but some filetests had to change since the canonical way of printing the CLIF constants is now in the preamble.
This commit makes the following changes to unwind information generation in
Cranelift:
* Remove frame layout change implementation in favor of processing the prologue
and epilogue instructions when unwind information is requested. This also
means this work is no longer performed for Windows, which didn't utilize it.
It also helps simplify the prologue and epilogue generation code.
* Remove the unwind sink implementation that required each unwind information
to be represented in final form. For FDEs, this meant writing a
complete frame table per function, which wastes 20 bytes or so for each
function with duplicate CIEs. This also enables Cranelift users to collect the
unwind information and write it as a single frame table.
* For System V calling convention, the unwind information is no longer stored
in code memory (it's only a requirement for Windows ABI to do so). This allows
for more compact code memory for modules with a lot of functions.
* Deletes some duplicate code relating to frame table generation. Users can
now simply use gimli to create a frame table from each function's unwind
information.
Fixes#1181.
- Undo temporary changes to default features (`all-arch`) and a
signal-handler test.
- Remove `SIGTRAP` handler: no longer needed now that we've found an
"undefined opcode" option on ARM64.
- Rename pp.rs to pretty_print.rs in machinst/.
- Only use empty stack-probe on non-x86. As per a comment in
rust-lang/compiler-builtins [1], LLVM only supports stack probes on
x86 and x86-64. Thus, on any other CPU architecture, we cannot refer
to `__rust_probestack`, because it does not exist.
- Rename arm64 to aarch64.
- Use `target` directive in vcode filetests.
- Run the flags verifier, but without encinfo, when using new backends.
- Clean up warning overrides.
- Fix up use of casts: use u32::from(x) and siblings when possible,
u32::try_from(x).unwrap() when not, to avoid silent truncation.
- Take immutable `Function` borrows as input; we don't actually
mutate the input IR.
- Lots of other miscellaneous cleanups.
[1] cae3e6ea23/src/probestack.rs (L39)
This patch ties together the new backend infrastructure with the
existing Cranelift codegen APIs.
With all patches in this series up to this patch applied, the ARM64
compiler is now functional and can be used. Two uses of this
functionality -- filecheck-based tests and integration into wasmtime --
will come in subsequent patches.
- Add a `simple_legalize()` function that invokes a predetermined set of
legalizations, without depending on the details of the current
backend design. This will be used by the new backend pipeline.
- Separate out `has_side_effect()` from the DCE pass. This will be used
by the new backends' lowering code.
- Add documentation for the `Arm64Call` relocation type.
This is a rebase of [1]. In the long term, we'll want to simplify these
analysis passes. For now, this is simple and will reduce the number of
instructions processed in certain cases.
[1] https://github.com/bytecodealliance/cranelift/pull/866
