T0b1/wasmtime
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

Document a caveat regarding max_wasm_stack (#4295)

Browse Source 
* Document a caveat regarding `max_wasm_stack`

Specifically, that the `max_wasm_stack` only limits the stack that can
be consumed by wasm, but it does not guarantee that the so much stack
space will be available.

* rustfmt

* Fix the claim about reseting the stack limit.
This commit is contained in:
Sergei Shulepov
2022-06-22 21:02:47 +02:00
committed by GitHub
parent 25a588c35f
commit b48b10b2aa
1 changed files with 24 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

27
crates/wasmtime/src/config.rs
View File

@@ -494,12 +494,33 @@ impl Config {
/// If a wasm call (or series of nested wasm calls) take more stack space
/// than the `size` specified then a stack overflow trap will be raised.
///
/// Caveat: this knob only limits the stack space consumed by wasm code.
/// More importantly, it does not ensure that this much stack space is
/// available on the calling thread stack. Exhausting the thread stack
/// typically leads to an **abort** of the process.
///
/// Here are some examples of how that could happen:
///
/// - Let's assume this option is set to 2 MiB and then a thread that has
/// a stack with 512 KiB left.
///
/// If wasm code consumes more than 512 KiB then the process will be aborted.
///
/// - Assuming the same conditions, but this time wasm code does not consume
/// any stack but calls into a host function. The host function consumes
/// more than 512 KiB of stack space. The process will be aborted.
///
/// There's another gotcha related to recursive calling into wasm: the stack
/// space consumed by a host function is counted towards this limit. The
/// host functions are not prevented from consuming more than this limit.
/// However, if the host function that used more than this limit and called
/// back into wasm, then the execution will trap immediatelly because of
/// stack overflow.
///
/// When the `async` feature is enabled, this value cannot exceed the
/// `async_stack_size` option. Be careful not to set this value too close
/// to `async_stack_size` as doing so may limit how much stack space
/// is available for host functions. Unlike wasm functions that trap
/// on stack overflow, a host function that overflows the stack will
/// abort the process.
/// is available for host functions.
///
/// By default this option is 512 KiB.
///