[lldb-dev] strange issues on linux
Ewan Crawford
ewan at codeplay.com
Mon Jun 1 10:53:37 PDT 2015
Hi Ryan,
I made changes to StopInfo recently to add the stack, r238323. I'll
have a closer look at this and see if I can figure out what's going on.
Thanks for bringing this up.
Best,
Ewan
On 01/06/2015 18:09, Ryan Brown wrote:
> I can't reproduce the server crash at the moment, but it was crashing
> immediately at process launch, so I don't think attaching to it would
> work.
>
> I think I found the other problem.
> ProcessGDBRemote now has a stack of stop infos.
> RefreshStateAfterStop loops through them and calls SetThreadStopInfo,
> which in turn calls UpdateThreadListIfNecessary.
> But what if these stop infos have different thread lists? Which do you
> believe? Currently the first update succeeds and then the others seem
> to be ignored because the stop info hasn't changed.
>
> So ignoring the threads for the 2nd stop packet is part of the
> problem. But why are there two in the first place?
> ProcessGDBRemote::DoLaunch calls SetLastStopPacket which pushes the
> packet onto the stack. But then it directly calls SetThreadStopInfo,
> bypassing RefreshStateAfterStop. So the packet stays on the stack and
> gets processed again along with the next stop packet.
>
> -- Ryan Brown
>
> On Mon, Jun 1, 2015 at 3:35 AM, Pavel Labath <labath at google.com
> <mailto:labath at google.com>> wrote:
>
> Hello,
>
> I'm not really sure what is going on, but I don't think the problem is
> in the server component. The server reports the correct register
> values. You say your plugin does not do anything which should change
> the registers (and the packet log confirms this), so it looks like the
> corruption happens in LLDB. I'm afraid I don't know enough about the
> client to know what is the problem, but it seems like you are hitting
> some kind of a race there. Possibly you are reading the register
> values before they have been populated (possibly even before the whole
> thread list is populated, which could explain why you are getting
> inconsistent thread counts).
>
> On 29 May 2015 at 17:15, Ryan Brown <ribrdb at google.com
> <mailto:ribrdb at google.com>> wrote:
> > It seemed like this is the way to connect to an already running
> gdbserver. I
> > was trying to see the output of gdb server to see why it was
> crashing.
> > Although I suppose the "OS or CPU not supported!" message might
> just mean I
> > started lldb-server with the wrong args and not the real problem.
> Yeah, debugging the server is not very easy. I usually just attach to
> a running instance, or load the resulting core file. As I said, this
> looks like a client issue, but it should still not crash the server.
> If you encounter a server crash (without using "process connect"), I
> would be interested in it and can probably fix it.
>
>
> > Here's a log from one session:
> >
>
> <snip>
>
> > < 588> read packet:
> >
> $T05thread:5cdf;name:vc.test;threads:5cd5,5cdb,5cdc,5cdd,5cde,5cdf,5ce0,5ce1,5ce2,5ce3;00:883e4c08c2000000;01:0000000000000000;02:401a0008c2000000;03:90d3950000000000;04:0000000000000000;05:683f4c08c2000000;06:78d5ab0000000000;07:083e4c08c2000000;08:2e8d685500000000;09:0700000000000000;0a:403d053600000000;0b:7b00000000000000;0c:1100000000000000;0d:7cc4950000000000;0e:0800000000000000;0f:0000000000000000;10:79f1490000000000;11:4602000000000000;12:3300000000000000;13:0000000000000000;14:0000000000000000;15:2b00000000000000;16:0000000000000000;17:0000000000000000;reason:breakpoint;#14
> This is the packet notifying the client you've hit a breakpoint. It
> also provides the values of the general purpose registers. The values
> seem reasonable here.
> After this, you are only doing memory read commands, and these should
> not affect the registers.
>
>
> > (lldb) register read
> > General Purpose Registers:
> > rax = 0x0000000000000000
> > rbx = 0x0000000000000000
> > rcx = 0x0000000000000000
> > rdx = 0x0000000000000000
> > rdi = 0x0000000000000000
> > rsi = 0x0000000000000000
> > rbp = 0x0000000000000000
> > rsp = 0x00007fffffffdde0
> > r8 = 0x0000000000000000
> > r9 = 0x0000000000000000
> > r10 = 0x0000000000000000
> > r11 = 0x0000000000000000
> > r12 = 0x0000000000000000
> > r13 = 0x0000000000000000
> > r14 = 0x0000000000000000
> > r15 = 0x0000000000000000
> > rip = 0x00007ffff7ddb2d0
> > rflags = 0x0000000000000200
> > cs = 0x0000000000000033
> > fs = 0x0000000000000000
> > gs = 0x0000000000000000
> > ss = 0x000000000000002b
> > ds = 0x0000000000000000
> > es = 0x0000000000000000
> "register read" does not need to issue any new server commands, since
> it thinks the register values have already been provided. However, it
> seems they got corrupted on their way...
>
>
> hope this helps,
> pl
>
>
>
>
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--
Ewan Crawford
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