queue-name parameter

Fernando_Bunn · July 18, 2019, 11:23pm

Hi, everyone.
I’m seeing an issue when using the -q parameter on a breakpoint using Xcode.

when I run:

(lldb) help breakpoint modify
I see this:

-q ( --queue-name )
The breakpoint stops only for threads in the queue whose name is
given by this argument.

So far, so good.
Then I try to set a breakpoint with -q on it like so:
(lldb) breakpoint set --file ViewController.swift --line 27 -q com.apple.main-thread

This doesn’t seem to work, but if I use -Q (uppercase), it works just fine.

I thought that there was a typo somewhere and even had a patch ready to submit changing the CommandObjectBreakpoint.cpp file
from this:

{ LLDB_OPT_SET_1, false, “queue-name”, ‘q’, OptionParser::eRequiredArgument, nullptr, {}, 0, eArgTypeQueueName, “The breakpoint stops only for threads in the queue whose name is given by this argument.” },

to this:

{ LLDB_OPT_SET_1, false, “queue-name”, ‘Q’, OptionParser::eRequiredArgument, nullptr, {}, 0, eArgTypeQueueName, “The breakpoint stops only for threads in the queue whose name is given by this argument.” },

jingham · July 19, 2019, 12:27am

Fernando, I don't see quite what you do. For me, -Q never sets the queue. Rather, the current Xcode version of lldb seems to have a bug where it doesn't reject illegal options, so the -Q argument is silently discarded. That would cause the breakpoint to "work" but it won't only stop on one queue. So I see:

(lldb) break set -f main.c -l 10 -q whatever
Breakpoint 1: where = SomeTool`main + 22 at main.c:13:3, address = 0x0000000100000f66
(lldb) break list 1
1: file = 'main.c', line = 10, exact_match = 0, locations = 1, resolved = 1, hit count = 0 Options: enabled queue name: "whatever"
1.1: where = SomeTool`main + 22 at main.c:13:3, address = 0x0000000100000f66, resolved, hit count = 0

That's right, it got the queue name and should match against it. But:

(lldb) break set -f main.c -l 10 -Q whatever
Breakpoint 2: where = SomeTool`main + 22 at main.c:13:3, address = 0x0000000100000f66
(lldb) break list 2
2: file = 'main.c', line = 10, exact_match = 0, locations = 1, resolved = 1, hit count = 0
2.1: where = SomeTool`main + 22 at main.c:13:3, address = 0x0000000100000f66, resolved, hit count = 0

That one didn't get a queue name at all. So it will always stop, but OTOH that's not really what you wanted.

It sounds like what is really going on is that the queue matching isn't working as you expected, so when you actually DID set a queue name - using the "-q" option, the breakpoint wasn't stopping, but when you didn't set a queue name (with the bogus -Q option) it did stop. So there might be something going wrong with the queue name matching?

Note, this bug doesn't exist in current llvm TOT. If you try with that lldb:

(lldb) break set -f foo.c -l 10 -Q foo
error: unknown or ambiguous option

That's right, there is no -Q option...

I'm surprised we have no tests for rejecting illegal options in the command interpreter, but I couldn't find any...

Jim

Fernando_Bunn · July 19, 2019, 10:20am

Jim,
you’re right, I was getting a false positive with -Q, sorry for the confusion.

So it seems I’m having 2 issues on Xcode, right?
A - No rejection of illegal options (-Q)
B - “-q” with the correct queue name is not working.

Here’s what I’m doing for B:

1 - (lldb) thread info
thread #1: tid = 0xfc5f, 0x00000001070418f4 ThreadTest`ViewController.viewDidLoad(self=0x00007f940610d270) at ViewController.swift:16:9, queue = ‘com.apple.main-thread’, stop reason = breakpoint 1.1

2 - (lldb) breakpoint set --file ViewController.swift --line 26 -q com.apple.main-thread
Breakpoint 2: where = ThreadTest`ThreadTest.ViewController.viewDidLoad() → () + 942 at ViewController.swift:26:15, address = 0x0000000107041c0e

3 - (lldb) breakpoint list 2
2: file = ‘ViewController.swift’, line = 26, exact_match = 0, locations = 1, resolved = 1, hit count = 0 Options: enabled queue name: “com.apple.main-thread”
2.1: where = ThreadTest`ThreadTest.ViewController.viewDidLoad() → () + 942 at ViewController.swift:26:15, address = 0x0000000107041c0e, resolved, hit count = 0

On #1 I just make sure the queue name is correct, com.apple.main-thread, then on #2 I set the breakpoint with “-q”, and on #3 I make sure that the parameter was set correctly, and I do see the enabled queue name: “com.apple.main-thread” in there, but the breakpoint is never executed.

But if I set breakpoint set --file ViewController.swift --line 26, without -q, the breakpoint is executed normally.
And to check that the queue name is “com.apple.main-thread” when this breakpoint is executed I did the following:

1 - (lldb) breakpoint set --file ViewController.swift --line 26
Breakpoint 3: where = ThreadTestThreadTest.ViewController.viewDidLoad() -> () + 942 at ViewController.swift:26:15, address = 0x0000000104a01c0e **2 - (lldb) c** Process 1242 resuming **3 - (lldb) thread info** thread #1: tid = 0x11cd2, 0x0000000104a01c0e ThreadTestViewController.viewDidLoad(self=0x00007fcb15d09d50) at ViewController.swift:26:15, queue = ‘com.apple.main-thread’, stop reason = breakpoint 3.1

I can verify that on #3 the queue name is in fact com.apple.main-thread but if I add -q com.apple.main-thread, it doesn’t work.

At this point, I’m not sure what to do next, maybe file a radar with Apple?
Thanks for your help, I really appreciate it

jingham · July 22, 2019, 5:18pm

I already filed both of these issues with Apple. If you want to file them too, feel free. I'll dup them to the ones I filed but that way you will get notification when they get fixed. These are also general lldb issues, so it would be good to file something with http://bugs.llvm.org.

Jim

Fernando_Bunn · February 18, 2020, 10:55pm

Jim,
filed here: FB7587703 (better late than never I guess)

thanks