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Avoid using String while holding an internal libobjc lock. #938

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merged 1 commit into from
Feb 3, 2025
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Avoid using String while holding an internal libobjc lock. #938

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28 changes: 23 additions & 5 deletions Sources/Testing/Discovery+Platform.swift
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Original file line number Diff line number Diff line change
Expand Up @@ -47,6 +47,25 @@ struct SectionBounds: Sendable {
#if SWT_TARGET_OS_APPLE
// MARK: - Apple implementation

extension SectionBounds.Kind {
/// The Mach-O segment and section name for this instance as a pair of
/// null-terminated UTF-8 C strings and pass them to a function.
///
/// The values of this property within this function are instances of
/// `StaticString` rather than `String` because the latter's inner storage is
/// sometimes Objective-C-backed and touching it here can cause a recursive
/// access to an internal libobjc lock, whereas `StaticString`'s internal
/// storage is immediately available.
fileprivate var segmentAndSectionName: (segmentName: StaticString, sectionName: StaticString) {
switch self {
case .testContent:
("__DATA_CONST", "__swift5_tests")
case .typeMetadata:
("__TEXT", "__swift5_types")
}
}
}

/// An array containing all of the test content section bounds known to the
/// testing library.
private let _sectionBounds = Locked<[SectionBounds.Kind: [SectionBounds]]>()
Expand Down Expand Up @@ -77,18 +96,17 @@ private let _startCollectingSectionBounds: Void = {

// If this image contains the Swift section(s) we need, acquire the lock and
// store the section's bounds.
func findSectionBounds(forSectionNamed segmentName: String, _ sectionName: String, ofKind kind: SectionBounds.Kind) {
for kind in SectionBounds.Kind.allCases {
let (segmentName, sectionName) = kind.segmentAndSectionName
var size = CUnsignedLong(0)
if let start = getsectiondata(mh, segmentName, sectionName, &size), size > 0 {
if let start = getsectiondata(mh, segmentName.utf8Start, sectionName.utf8Start, &size), size > 0 {
let buffer = UnsafeRawBufferPointer(start: start, count: Int(clamping: size))
let sb = SectionBounds(imageAddress: mh, buffer: buffer)
_sectionBounds.withLock { sectionBounds in
sectionBounds[kind]!.append(sb)
}
}
}
findSectionBounds(forSectionNamed: "__DATA_CONST", "__swift5_tests", ofKind: .testContent)
findSectionBounds(forSectionNamed: "__TEXT", "__swift5_types", ofKind: .typeMetadata)
}

#if _runtime(_ObjC)
Expand All @@ -97,7 +115,7 @@ private let _startCollectingSectionBounds: Void = {
}
#else
_dyld_register_func_for_add_image { mh, _ in
addSectionBounds(from: mh)
addSectionBounds(from: mh!)
}
#endif
}()
Expand Down