Skip to content

[Swift] Fixes load from misaligned raw pointer #8649

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
mustiikhalil merged 2 commits into from
Jul 29, 2025
Merged

[Swift] Fixes load from misaligned raw pointer #8649

Show file tree
Hide file tree
Changes from 1 commit
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
fdfd316
[Swift] Fix misaligned pointer
mustiikhalil Jul 26, 2025
b89f2dc
Merge branch 'master' into fix-fatal-error-load-misaligned-pointer
aardappel Jul 29, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
4 changes: 2 additions & 2 deletions swift/Sources/FlatBuffers/FlatBufferBuilder.swift
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -303,12 +303,12 @@ public struct FlatBufferBuilder {
var isAlreadyAdded: Int?

let vt2 = _bb.memory.advanced(by: _bb.writerIndex)
let len2 = vt2.load(fromByteOffset: 0, as: Int16.self)
let len2 = vt2.bindMemory(to: Int16.self, capacity: 1).pointee

for index in stride(from: 0, to: _vtables.count, by: 1) {
let position = _bb.capacity &- Int(_vtables[index])
let vt1 = _bb.memory.advanced(by: position)
let len1 = _bb.read(def: Int16.self, position: position)
let len1 = vt1.bindMemory(to: Int16.self, capacity: 1).pointee
if len2 != len1 || 0 != memcmp(vt1, vt2, Int(len2)) { continue }

isAlreadyAdded = Int(_vtables[index])
Expand Down
16 changes: 16 additions & 0 deletions tests/swift/Tests/Flatbuffers/FlatBuffersTests.swift
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -120,6 +120,22 @@ final class FlatBuffersTests: XCTestCase {
XCTAssertEqual(scalarTable.justEnum, .one)
XCTAssertNil(scalarTable.maybeEnum)
}

func testAlignmentCrash() {
var builder = FlatBufferBuilder(initialSize: 256)

// Create two identical tables to trigger vtable deduplication
let str1 = builder.create(string: "test")
let start1 = builder.startTable(with: 1)
builder.add(offset: str1, at: 0)
_ = builder.endTable(at: start1)

// Second table triggers vtable comparison where crash occurs
let str2 = builder.create(string: "crash")
let start2 = builder.startTable(with: 1)
builder.add(offset: str2, at: 0)
_ = builder.endTable(at: start2) // ← Crashes here on ARM64
}
}

class Country {
Expand Down
Loading