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Fix the SFI-reading heuristic for Node v24+ #270

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Merged
umanwizard merged 2 commits into from
May 14, 2026
Merged

Fix the SFI-reading heuristic for Node v24+ #270

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7c80371
Fix the SFI-reading heuristic for Node v24+
umanwizard May 13, 2026
9b79449
fix coredump test
umanwizard May 14, 2026
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31 changes: 30 additions & 1 deletion interpreter/nodev8/v8.go
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Original file line number Diff line number Diff line change
Expand Up @@ -966,6 +966,26 @@ func (i *v8Instance) analyzeScopeInfo(ptr libpf.Address) (name libpf.String,
return libpf.NullString, 0, 0
}

// Starting in this version, position start and end
// were moved to fixed locations before the variable-length data,
// so we no longer need a heuristic to find them (and in fact, our
// heuristic doesn't work).
// See https://chromium-review.googlesource.com/c/v8/v8/+/5627032
// for where the change was made.
isOld := i.d.version < v8Ver(12, 8, 44)
if !isOld {
// As of today [2026-05-13] these haven't changed since
// they were introduced [2024-06-13]. That's scarcely two years,
// so maybe they'll change in the future; at any rate, there doesn't seem to be a way to
// derive them from symbols.
//
// See https://chromium.googlesource.com/v8/v8.git/+/refs/tags/12.8.44/src/objects/scope-info.tq#125
positionInfoStartIdx := 3
positionInfoEndIdx := 4

startPos = int(npsr.Uint64(slotData, uint(positionInfoStartIdx*slotSize)))
endPos = int(npsr.Uint64(slotData, uint(positionInfoEndIdx*slotSize)))
}
// Skip reserved slots and the context locals
ndx := int(vms.ScopeInfoIndex.FirstVars)
ndx += 2 * int(decodeSMI(npsr.Uint64(slotData,
Expand All @@ -980,7 +1000,12 @@ func (i *v8Instance) analyzeScopeInfo(ptr libpf.Address) (name libpf.String,
// assume that first valid string is the function name
name, _ = i.getString(libpf.Address(cur), 0)
}
if isSMI(cur) && isSMI(prev) {
// In recent versions, we'll have already found the begin/end positions at
// fixed indices, so just return. See the comment where isOld is defined for details.
if !isOld && name != libpf.NullString {
return name, startPos, endPos
}
if isOld && isSMI(cur) && isSMI(prev) {
// Assume that two numbers (first one lower than the second)
// is the start/end position pair. This also follows after
// function name, so break when found.
Expand All @@ -992,6 +1017,10 @@ func (i *v8Instance) analyzeScopeInfo(ptr libpf.Address) (name libpf.String,
}
prev = cur
}
if !isOld {
// even if we didn't find name, we can be reasonably sure start/end are right, so return them
return name, startPos, endPos
}
return name, 0, 0
}

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2 changes: 1 addition & 1 deletion tools/coredump/testdata/arm64/node-hidden-internal-symbols.json
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Expand Up @@ -13,7 +13,7 @@
"node+0xb42107",
"node+0xa46483",
"V8::UnknownFrame+0 in :0",
"utf8+0 in /local/hello3.js:0",
"utf8+0 in /local/hello3.js:1",
"<anonymous>+0 in node:internal/modules/cjs/loader:0",
"<anonymous>+0 in node:internal/modules/cjs/loader:0",
"<anonymous>+0 in node:internal/modules/cjs/loader:0",
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