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Fix a case of using the wrong stack map during gcs (#2396)

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This commit fixes an issue where when looking up the stack map for a pc
within a function we might end up reading the *previous* function's
stack maps. This then later caused asserts to trip because we started
interpreting random data as a `VMExternRef` when it wasn't. The fix was
to add `None` markers for "this range has no stack map" in the function
ranges map.

Closes #2386
This commit is contained in:
Alex Crichton
2020-11-12 13:24:00 -06:00
committed by GitHub
parent cbce34af0a
commit 068340d30f
2 changed files with 71 additions and 4 deletions
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26
crates/runtime/src/externref.rs
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@@ -779,8 +779,9 @@ struct ModuleStackMaps {
range: std::ops::Range<usize>,
/// A map from a PC in this module (that is a GC safepoint) to its
/// associated stack map.
pc_to_stack_map: Vec<(usize, Rc<StackMap>)>,
/// associated stack map. If `None` then it means that the PC is the start
/// of a range which has no stack map.
pc_to_stack_map: Vec<(usize, Option<Rc<StackMap>>)>,
}
impl StackMapRegistry {
@@ -797,6 +798,7 @@ impl StackMapRegistry {
let mut min = usize::max_value();
let mut max = 0;
let mut pc_to_stack_map = vec![];
let mut last_is_none_marker = true;
for (range, infos) in stack_maps {
let len = range.end - range.start;
@@ -804,12 +806,28 @@ impl StackMapRegistry {
min = std::cmp::min(min, range.start);
max = std::cmp::max(max, range.end);
// Add a marker between functions indicating that this function's pc
// starts with no stack map so when our binary search later on finds
// a pc between the start of the function and the function's first
// stack map it doesn't think the previous stack map is our stack
// map.
//
// We skip this if the previous entry pushed was also a `None`
// marker, in which case the starting pc already has no stack map.
// This is also skipped if the first `code_offset` is zero since
// what we'll push applies for the first pc anyway.
if !last_is_none_marker && (infos.is_empty() || infos[0].code_offset > 0) {
pc_to_stack_map.push((range.start, None));
last_is_none_marker = true;
}
for info in infos {
assert!((info.code_offset as usize) < len);
pc_to_stack_map.push((
range.start + (info.code_offset as usize),
Rc::new(info.stack_map.clone()),
Some(Rc::new(info.stack_map.clone())),
));
last_is_none_marker = false;
}
}
@@ -911,7 +929,7 @@ impl StackMapRegistry {
Err(n) => n - 1,
};
let stack_map = stack_maps.pc_to_stack_map[index].1.clone();
let stack_map = stack_maps.pc_to_stack_map[index].1.as_ref()?.clone();
Some(stack_map)
}
}