[SR-5438] Something is up with do/try/catch on the port to Android

[johnno1962]

Previous ID	SR-5438
Radar	None
Original Reporter	@johnno1962
Type	Bug
Status	Closed
Resolution	Done

Environment

http://johnholdsworth.com/android_toolchain.tgz

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, Android, Runtime
Assignee	None
Priority	Medium

md5: 811dce9ad8c11216c611c20e8ee4b825

relates to:

• SR-5414 ImageInspectionELF.cpp:getSectionInfo crashes on Android

Issue Description:

I’ve been chipping away at getting Swift to work on Android and found that there are problems with the implementation of do/try/catch when swift is run an Android device.

The following example program:

import Foundation

print("Hello, Android")

do {
      print("HERE1")
      try { throw NSError(domain:"Oh", code:-1) }()
}
catch let err as Error {
      print("HERE2")
}

print("DONE")

Produces this output on Linux/macOS:

Hello, Android
HERE1
HERE2
DONE

Whereas on Android following the instructions from https://github.com/apple/swift/blob/master/docs/Android.md

produces the following output:

Hello, Android
HERE1
DONE

This is causing crashes in corefoundation where errors should have been trapped and code goes down the wrong path as a result. This is from a version of Swift from master about a month ago. I’ll be building from a more up to date version soon and will close this report if this is resolved.

[johnno1962]

I’ve updated https://bugs.swift.org/browse/SR-5414 which is thhe only other known problem with the Swift runtime which I though might be related to this problem. This seems not to be the case. It just seems thrown exceptions are not caught at all on the Android port of Swift.

[johnno1962]

If I alter the code to the following:

import Foundation

print("Hello, Android")

do {
      print("HERE1")
      try { throw NSError(domain:"Oh", code:-1) }()
      print("HERE!")
}
//catch let err as Error {
catch {
      print("HERE2")
}

print("DONE”)

You can see the throw isn’t working at all

Hello, Android
HERE1
HERE!
DONE

[johnno1962]

I’ve raised a PR on swift-llvm apple/swift-llvm#55 to resolve this. The problem was r8 was being saved and restored on entry/return from functions that throw. This was overwriting the value for r8 which was intended to be the object being thrown resulting in calling code failing to catch the exception.

[johnno1962]

{{ ldr r0, [r11, #-40]
bl swift_willThrow
ldr r0, [r11, #-40]
mov r8, r0
sub sp, r11, #8
pop {r8, r10, r11, pc}
}}