* 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
* Add a spec test fuzzer for Config
This commit adds a new fuzzer which is intended to run on oss-fuzz. This
fuzzer creates and arbitrary `Config` which *should* pass spec tests and
then asserts that it does so. The goal here is to weed out any
accidental bugs in global configuration which could cause
non-spec-compliant behavior.
* Move implementation to `fuzzing` crate
... but turn it back on in CI by default. The `binaryen-sys` crate
builds binaryen from source, which is a drag on CI for a few reasons:
* This is quite large and takes a good deal of time to build
* The debug build directory for binaryen is 4GB large
In an effort to both save time and disk space on the builders this
commit adds a `binaryen` feature to the `wasmtime-fuzz` crate. This
feature is enabled specifically when running the fuzzers on CI, but it
is disabled during the typical `cargo test --all` command. This means
that the test builders should save an extra 4G of space and be a bit
speedier now that they don't build a giant wad of C++.
We'll need to update the OSS-fuzz integration to enable the `binaryen`
feature when executing `cargo fuzz build`, and I'll do that once this
gets closer to landing.
We only generate *valid* sequences of API calls. To do this, we keep track of
what objects we've already created in earlier API calls via the `Scope` struct.
To generate even-more-pathological sequences of API calls, we use [swarm
testing]:
> In swarm testing, the usual practice of potentially including all features
> in every test case is abandoned. Rather, a large “swarm” of randomly
> generated configurations, each of which omits some features, is used, with
> configurations receiving equal resources.
[swarm testing]: https://www.cs.utah.edu/~regehr/papers/swarm12.pdf
There are more public APIs and instance introspection APIs that we have than
this fuzzer exercises right now. We will need a better generator of valid Wasm
than `wasm-opt -ttf` to really get the most out of those currently-unexercised
APIs, since the Wasm modules generated by `wasm-opt -ttf` don't import and
export a huge variety of things.
When the test case that causes the failure can successfully be disassembled to
WAT, we get logs like this:
```
[2019-11-26T18:48:46Z INFO wasmtime_fuzzing] Wrote WAT disassembly to: /home/fitzgen/wasmtime/crates/fuzzing/target/scratch/8437-0.wat
[2019-11-26T18:48:46Z INFO wasmtime_fuzzing] If this fuzz test fails, copy `/home/fitzgen/wasmtime/crates/fuzzing/target/scratch/8437-0.wat` to `wasmtime/crates/fuzzing/tests/regressions/my-regression.wat` and add the following test to `wasmtime/crates/fuzzing/tests/regressions.rs`:
```
#[test]
fn my_fuzzing_regression_test() {
let data = wat::parse_str(
include_str!("./regressions/my-regression.wat")
).unwrap();
oracles::instantiate(data, CompilationStrategy::Auto)
}
```
```
If the test case cannot be disassembled to WAT, then we get logs like this:
```
[2019-11-26T18:48:46Z INFO wasmtime_fuzzing] Wrote Wasm test case to: /home/fitzgen/wasmtime/crates/fuzzing/target/scratch/8437-0.wasm
[2019-11-26T18:48:46Z INFO wasmtime_fuzzing] Failed to disassemble Wasm into WAT:
Bad magic number (at offset 0)
Stack backtrace:
Run with RUST_LIB_BACKTRACE=1 env variable to display a backtrace
[2019-11-26T18:48:46Z INFO wasmtime_fuzzing] If this fuzz test fails, copy `/home/fitzgen/wasmtime/crates/fuzzing/target/scratch/8437-0.wasm` to `wasmtime/crates/fuzzing/tests/regressions/my-regression.wasm` and add the following test to `wasmtime/crates/fuzzing/tests/regressions.rs`:
```
#[test]
fn my_fuzzing_regression_test() {
let data = include_bytes!("./regressions/my-regression.wasm");
oracles::instantiate(data, CompilationStrategy::Auto)
}
```
```
