Hi Shawn,
Thanks for your additional patch. I tried it and fixes this issue. This
patch and the IOHandler one certainly fix a bunch of problems. I'll help
you push to get these patches upstream when Todd and Greg come back off
vacation.
I see what you mean about the launching code pushing an IOHandler.
Perhaps it's because the launching sequence fork/ptrace(TRACEME)/exec
may result in some output before the process traps? That's the only
rationale I can think of... but since the main thread (the one doing the
Launch) blocks in WaitForProcessStopPrivate, that's not adequate reason IMO.
Your point about the first stop being made public/broadcasted being by
design seems possible, but it seems wrong to me since the average user
when they launch a program in a debugger is probably not interested in
knowing that ptrace causes a stop in the TRACEME invocation. gdb
certainly does not:
(gdb) file ./i64-hello.elf
Reading symbols from
/home/mg11/src/main/devtools/main/heracles/csrgdbserver/test/examples/simple/i64-hello.elf...done.
(gdb) run
Starting program: ./i64-hello.elf
I think I'll spend the rest of the day trying to figure out why
ShouldBroadcast is returning true for this first stop. Keep your ideas
coming in - we need to get these fixes in!
thanks
Matt
Shawn Best wrote:
Hi Matthew,
I have also been tracking this bug. I believe there are other bugs in
the unit tests failing indirectly because of this. I also have a
patch that will fix it, but was sitting on it until the other one
landed. These bugs do not show up on OSX since the inferiors are
launched separately then attached to.
The first odd thing the launching code does is push an IOHandler when
it sees the state transition to 'launching'. This is odd because I
believe the launching program will always come up in a stopped state
which will immediately pop the IOHandler.
At launch, the process comes up in the stopped state. The launch code
manually calls HandlePrivateEvent() with the stop event, which then
broadcasts the Event. When HandleProcessEvent gets the public stop,
it dumps out the current thread state just as if an executing inferior
hit a breakpoint and stopped.
One way to fix this would be:
1. Don't push io handler when state is 'launching'
2. Instead of manually calling HandlePrivateEvent, call SetPublicState().
Alternately, we could try and debug why ShouldBroadcast() returns
true, but that appears to be by design since it is expecting the
public stop event to pop the IOHandler that had been pushed when
launching.
I have attached a patch demonstrating this. In conjunction with the
other patch for IOHandler race condition, it will fix a bunch of this
kind of behaviour.
Shawn.
On 8/5/2014 6:59 AM, Matthew Gardiner wrote:
Jim,
I've been trying to debug an issue (I see it on 64-bit linux) where,
I do "target create" and "process launch" and despite not requesting
*stop at entry*, the first stop (which I believe is just the initial
ptrace attach stop) is reported to the lldb command line. I added
some fprintf to Process::HandlePrivateEvent, which counts the number
of eStoppedState events seen and whether ShouldBroadcastEvent returns
true for this event. Here's the output from my program with diagnostic:
(lldb) target create ~/me/i64-hello.elf
Current executable set to '~/me/i64-hello.elf' (x86_64).
(lldb) process launch
MG Process::HandlePrivateEvent launching stopped_count 0
should_broadcast 1
Process 31393 launching
MG Process::HandlePrivateEvent stopped stopped_count 1
should_broadcast 1
MG Process::HandlePrivateEvent running stopped_count 1
should_broadcast 1
Process 31393 launched: 'i64-hello.elf' (x86_64)
Process 31393 stopped
* thread #1: tid = 31393, 0x0000003675a011f0, name = 'i64-hello.elf',
stop reason = trace
frame #0: 0x0000003675a011f0
-> 0x3675a011f0: movq %rsp, %rdi
0x3675a011f3: callq 0x3675a046e0
0x3675a011f8: movq %rax, %r12
0x3675a011fb: movl 0x21eb97(%rip), %eax
(lldb) MG Process::HandlePrivateEvent stopped stopped_count 2
should_broadcast 0
MG Process::HandlePrivateEvent running stopped_count 2
should_broadcast 0
MG Process::HandlePrivateEvent stopped stopped_count 3
should_broadcast 0
MG Process::HandlePrivateEvent running stopped_count 3
should_broadcast 0
In summary, lldb reports the inferior to be stopped (even though
/proc/pid/status and lldb "target list" say it is running). Clearly
this is wrong (hence my earlier post).
Am I correct in assuming that when ShouldBroadcastEvent returns true
this means that lldb should show this event to the debug user? (And
thus hide other events where ShouldBroadcastEvent=false).
What puzzled me was why ShouldBroadcastEvent return true for this
very first stop. Is this a bug?
I also spent sometime at ShouldBroadcastEvent and saw that this:
case eStateStopped:
case eStateCrashed:
case eStateSuspended:
{
....
if (was_restarted || should_resume ||
m_resume_requested)
{
evaluates as false, and hence the PrivateResume code is not called...
does this seem buggy to you for this very first stop?
I thought I'd try asking you, since in a previous mail from Greg, he
cited you as being a thread-plan expert. (Hope that's ok!). I'd
really appreciate your help in clarifying the above questions for me,
and if you have time, giving me some ideas as to how to trace this
one further e.g. how m_thread_list.ShouldStop and
m_thread_list.ShouldReportStop should behave, etc.
thanks for your help
Matt
Matthew Gardiner wrote:
Folks,
In addition to the overlapping prompt race Shawn Best and myself are
looking at, I'm seeing another issue where if I launch a process, I
get a stop (presumably the in) being reported to the UI.
(lldb) target create ~/mydir/i64-hello.elf
Current executable set to '~/mydir/i64-hello.elf' (x86_64).
(lldb) process launch
Process 27238 launching
Process 27238 launched: '64-hello.elf' (x86_64)
Process 27238 stopped
* thread #1: tid = 27238, 0x0000003675a011f0, name = 'i64-hello.elf'
frame #0:
(lldb) target list
Current targets:
* target #0: i64-hello.elf ( arch=x86_64-unknown-linux,
platform=host, pid=27238, state=running )
(lldb)
As you can see the "target list" reflects that the process is
running. Which I confirmed by looking at /proc/27238/status.
Anyone else seeing this?
thanks
Matt
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