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Wasmtime: fix stack walking across frames from different stores (#4779)

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We were previously implicitly assuming that all Wasm frames in a stack used the
same `VMRuntimeLimits` as the previous frame we walked, but this is not true
when Wasm in store A calls into the host which then calls into Wasm in store B:

    | ...             |
    | Host            |  |
    +-----------------+  | stack
    | Wasm in store A |  | grows
    +-----------------+  | down
    | Host            |  |
    +-----------------+  |
    | Wasm in store B |  V
    +-----------------+

Trying to walk this stack would previously result in a runtime panic.

The solution is to push the maintenance of our list of saved Wasm FP/SP/PC
registers that allow us to identify contiguous regions of Wasm frames on the
stack deeper into `CallThreadState`. The saved registers list is now maintained
whenever updating the `CallThreadState` linked list by making the
`CallThreadState::prev` field private and only accessible via a getter and
setter, where the setter always maintains our invariants.
This commit is contained in:
Nick Fitzgerald
2022-08-30 11:28:00 -07:00
committed by GitHub
parent 09c93c70cc
commit ff0e84ecf4
7 changed files with 492 additions and 94 deletions
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16
crates/runtime/src/traphandlers/backtrace.rs
View File

@@ -149,18 +149,18 @@ impl Backtrace {
// trace through (since each `CallTheadState` saves the *previous*
// call into Wasm's saved registers, and the youngest call into
// Wasm's registers are saved in the `VMRuntimeLimits`)
if state.prev.get().is_null() {
debug_assert_eq!(state.old_last_wasm_exit_pc, 0);
debug_assert_eq!(state.old_last_wasm_exit_fp, 0);
debug_assert_eq!(state.old_last_wasm_entry_sp, 0);
if state.prev().is_null() {
debug_assert_eq!(state.old_last_wasm_exit_pc(), 0);
debug_assert_eq!(state.old_last_wasm_exit_fp(), 0);
debug_assert_eq!(state.old_last_wasm_entry_sp(), 0);
log::trace!("====== Done Capturing Backtrace ======");
return;
}
if let ControlFlow::Break(()) = Self::trace_through_wasm(
state.old_last_wasm_exit_pc,
state.old_last_wasm_exit_fp,
state.old_last_wasm_entry_sp,
state.old_last_wasm_exit_pc(),
state.old_last_wasm_exit_fp(),
state.old_last_wasm_entry_sp(),
&mut f,
) {
log::trace!("====== Done Capturing Backtrace ======");
@@ -266,7 +266,7 @@ impl Backtrace {
}
/// Iterate over the frames inside this backtrace.
pub fn frames<'a>(&'a self) -> impl Iterator<Item = &'a Frame> + 'a {
pub fn frames<'a>(&'a self) -> impl ExactSizeIterator<Item = &'a Frame> + 'a {
self.0.iter()
}
}