[SR-936] NSMutableData's hash() causes a segmentation fault on Linux

[swift-ci]

Previous ID	SR-936
Radar	None
Original Reporter	inket (JIRA User)
Type	Bug
Status	Resolved
Resolution	Done

Environment

Ubuntu 14.04, Swift version 3.0-dev (LLVM b361b0fc05, Clang 11493b0f62, Swift 24a0c3de75)

Reproduced on Ubuntu 16.04, Swift version 4.0.1-dev (LLVM 2dedb62a0b, Clang ab7472e733, Swift 7efb2d13a2)

Additional Detail from JIRA

Votes	3
Component/s	Foundation
Labels	Bug, Linux
Assignee	@spevans
Priority	Medium

md5: bf8cffe9642151374ef9e452574daaaf

relates to:

• SR-1547 NSData causes segmentation fault

Issue Description:

The current implementation of NSData's hash() causes a segmentation fault on Linux.

Using the REPL on Mac:

Welcome to Apple Swift version 3.0-dev (LLVM b361b0fc05, Clang 11493b0f62, Swift 24a0c3de75). Type :help for assistance.
  1> import Foundation
  2> "foobar".dataUsingEncoding(NSUTF8StringEncoding)?.hash
$R0: Int? = 114710658

on Linux:

Welcome to Swift version 3.0-dev (LLVM b361b0fc05, Clang 11493b0f62, Swift 24a0c3de75). Type :help for assistance.
  1> import Foundation
  2> "foobar".dataUsingEncoding(NSUTF8StringEncoding)?.hash
Execution interrupted. Enter code to recover and continue.

[swift-ci]

Comment by Christian Rishøj (JIRA)

A stack overflow appears to occur with NSMutableData, but not with NSData.

Reproducible with the following minimal test case (using Swift 2.2 on Ubuntu 14.04):

Welcome to Swift version 2.2-dev (LLVM 524cfeb800, Clang f66c5bb67b, Swift 870696170f). Type :help for assistance.
  1> import Foundation
  2> NSData().hash
$R0: Int = 0
  3> NSMutableData().hash
Execution interrupted. Enter code to recover and continue.
Enter LLDB commands to investigate (type :help for assistance.)

Backtrace snippet:

  4> :bt 10
* thread #​1: tid = 18075, 0x00007ffff429dd7c libFoundation.so`static Foundation.=== infix (Swift.AnyObject.Type, Swift.AnyObject.Type) -> Swift.Bool + 12, name = 'repl_swift', stop reason = signal SIGSEGV: invalid address (fault address: 0x7fffff7feff8)
  * frame #​0: 0x00007ffff429dd7c libFoundation.so`static Foundation.=== infix (Swift.AnyObject.Type, Swift.AnyObject.Type) -> Swift.Bool + 12
    frame #​1: 0x00007ffff4119c47 libFoundation.so`Foundation.NSData._cfObject.getter : __ObjC.CFData + 39
    frame #​2: 0x00007ffff411a051 libFoundation.so`Foundation.NSData.hash.getter : Swift.Int + 17
    frame #​3: 0x00007ffff429b03a libFoundation.so`Foundation._CFSwiftGetHash (Swift.AnyObject) -> Swift.UInt + 58
    frame #​4: 0x00007ffff429c50a libFoundation.so`@objc Foundation._CFSwiftGetHash (Swift.AnyObject) -> Swift.UInt + 26
    frame #​5: 0x00007ffff411a05d libFoundation.so`Foundation.NSData.hash.getter : Swift.Int + 29
    frame #​6: 0x00007ffff429b03a libFoundation.so`Foundation._CFSwiftGetHash (Swift.AnyObject) -> Swift.UInt + 58
    frame #​7: 0x00007ffff429c50a libFoundation.so`@objc Foundation._CFSwiftGetHash (Swift.AnyObject) -> Swift.UInt + 26
    frame #​8: 0x00007ffff411a05d libFoundation.so`Foundation.NSData.hash.getter : Swift.Int + 29
    frame #​9: 0x00007ffff429b03a libFoundation.so`Foundation._CFSwiftGetHash (Swift.AnyObject) -> Swift.UInt + 58

[tbkka]

I don't think this is related to SR-1547, as there's no error objects here. The key symptom of this bug is the endless mutual recursion between `_CFSwiftGetHash` and `NSData.hash.getter`.

I've seen that same symptom in a larger program that used Foundation.Data, but only on Linux, not on macOS. The workaround in that case was to first check if the data object was zero-length and not request the hashValue unless it had at least one byte.

[alblue]

The original issue seems to be fixed in 4.0.1-dev:

{{$ swift -I /usr/lib/swift/clang/include
Welcome to Swift version 4.0.1-dev (LLVM 2dedb62a0b, Clang ab7472e733, Swift 7efb2d13a2). Type :help for assistance.
1> import Foundation
2> "foobar".data(using:.utf8)?.hashValue
$R0: Int? = 114710658
}}

The second problem, that there is a recursive call on NSMutableData's hash, still seems to exist:

{{ 3> NSData().hash
$R1: Int = 0
4> NSMutableData().hash
Execution interrupted. Enter code to recover and continue.
Enter LLDB commands to investigate (type :help for assistance.)
Process 149 stopped

• thread Fixing whitespace formatting #1, name = 'repl_swift', stop reason = signal SIGSEGV: invalid address (fault address: 0x7fffff7feff8)
  frame #0: 0x00007ffff3bbf294 libFoundation.so`merged Foundation.NSData.length.getter : Swift.Int + 4
  libFoundation.so`merged Foundation.NSData.length.getter : Swift.Int:
  -> 0x7ffff3bbf294 <+4>: pushq %r15
  0x7ffff3bbf296 <+6>: pushq %r14
  0x7ffff3bbf298 <+8>: pushq %rbx
  0x7ffff3bbf299 <+9>: pushq %rax
  Target 0: (repl_swift) stopped.
  }}

[spevans]

Possible fix: #1669

[spevans]

Merged to `master` branch.