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[embedded] Fix a memory leak caused by incorrect refcounting logic around doNotFreeBit

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This commit is contained in:
Kuba Mracek
2024-10-18 23:19:40 -07:00
parent 2720316090
commit 8666aef39f
4 changed files with 91 additions and 14 deletions
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29
stdlib/public/core/EmbeddedRuntime.swift
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@@ -38,20 +38,21 @@ public struct HeapObject {
// to think about supporting (or banning) weak and/or unowned references.
var refcount: Int
// Note: The immortalRefCount value is also hard-coded in IRGen in `irgen::emitConstantObject`.
#if _pointerBitWidth(_64)
static let doNotFreeBit = Int(bitPattern: 0x8000_0000_0000_0000)
static let refcountMask = Int(bitPattern: 0x7fff_ffff_ffff_ffff)
static let doNotFreeBit = Int(bitPattern: 0x8000_0000_0000_0000)
static let refcountMask = Int(bitPattern: 0x7fff_ffff_ffff_ffff)
static let immortalRefCount = Int(bitPattern: 0x7fff_ffff_ffff_ffff) // Make sure we don't have doNotFreeBit set
#elseif _pointerBitWidth(_32)
static let doNotFreeBit = Int(bitPattern: 0x8000_0000)
static let refcountMask = Int(bitPattern: 0x7fff_ffff)
static let doNotFreeBit = Int(bitPattern: 0x8000_0000)
static let refcountMask = Int(bitPattern: 0x7fff_ffff)
static let immortalRefCount = Int(bitPattern: 0x7fff_ffff) // Make sure we don't have doNotFreeBit set
#elseif _pointerBitWidth(_16)
static let doNotFreeBit = Int(bitPattern: 0x8000)
static let refcountMask = Int(bitPattern: 0x7fff)
static let doNotFreeBit = Int(bitPattern: 0x8000)
static let refcountMask = Int(bitPattern: 0x7fff)
static let immortalRefCount = Int(bitPattern: 0x7fff) // Make sure we don't have doNotFreeBit set
#endif
// Note: The immortalRefCount value of -1 is also hard-coded in IRGen in `irgen::emitConstantObject`.
static let immortalRefCount = -1
#if _pointerBitWidth(_64)
static let immortalObjectPointerBit = UInt(0x8000_0000_0000_0000)
#endif
@@ -158,7 +159,7 @@ public func swift_initStaticObject(metadata: Builtin.RawPointer, object: Builtin
func swift_initStaticObject(metadata: UnsafeMutablePointer<ClassMetadata>, object: UnsafeMutablePointer<HeapObject>) -> UnsafeMutablePointer<HeapObject> {
_swift_embedded_set_heap_object_metadata_pointer(object, metadata)
object.pointee.refcount = HeapObject.immortalRefCount
object.pointee.refcount = HeapObject.immortalRefCount | HeapObject.doNotFreeBit
return object
}
@@ -251,7 +252,7 @@ public func swift_retain_n(object: Builtin.RawPointer, n: UInt32) -> Builtin.Raw
func swift_retain_n_(object: UnsafeMutablePointer<HeapObject>, n: UInt32) -> UnsafeMutablePointer<HeapObject> {
let refcount = refcountPointer(for: object)
if loadRelaxed(refcount) == HeapObject.immortalRefCount {
if loadRelaxed(refcount) & HeapObject.refcountMask == HeapObject.immortalRefCount {
return object
}
@@ -294,7 +295,8 @@ func swift_release_n_(object: UnsafeMutablePointer<HeapObject>?, n: UInt32) {
}
let refcount = refcountPointer(for: object)
if loadRelaxed(refcount) == HeapObject.immortalRefCount {
let loadedRefcount = loadRelaxed(refcount)
if loadedRefcount & HeapObject.refcountMask == HeapObject.immortalRefCount {
return
}
@@ -309,7 +311,8 @@ func swift_release_n_(object: UnsafeMutablePointer<HeapObject>?, n: UInt32) {
// There can only be one thread with a reference at this point (because
// we're releasing the last existing reference), so a relaxed store is
// enough.
storeRelaxed(refcount, newValue: HeapObject.immortalRefCount)
let doNotFree = (loadedRefcount & HeapObject.doNotFreeBit) != 0
storeRelaxed(refcount, newValue: HeapObject.immortalRefCount | (doNotFree ? HeapObject.doNotFreeBit : 0))
_swift_embedded_invoke_heap_object_destroy(object)
} else if resultingRefcount < 0 {