[lldb-dev] Linux issues where I am not getting breakpoints...

Thu Apr 13 05:48:52 PDT 2017

I seen a similar issue when trying to debug an application with a lot of
shared libraries (1000+) and in that case the problem was that lldb-server
was too slow to respond what caused a connection timeout in lldb.
Increasing plugin.process.gdb-remote.packet-timeout fixed the problem for
me but it would be great if we can make the jModulesInfo packet faster in
lldb-server.

Tamas

On Wed, Apr 12, 2017 at 11:33 PM Greg Clayton <clayborg at gmail.com> wrote:

> So the issue is with jModulesInfo. If it is too large we end up losing
> connection. Not sure if this is on the send or receive side yet. But if I
> comment out support for this packet, my debug sessions works just fine.
>
> Greg
>
> On Apr 12, 2017, at 10:42 AM, Greg Clayton <clayborg at gmail.com> wrote:
>
> What I now believe is happening is lldb-server is exiting for some reason
> and then the process just runs and still shows the output in LLDB because
> we hooked up the STDIO. I see lldb-server exits with an exit code of 0, but
> no command had been sent to terminate it. I will track that down.
>
> Also, log_channels in lldb-gdbserver.cpp is using a llvm::StringRef
> incorrectly:
>
>     case 'c': // Log Channels
>       if (optarg && optarg[0])
>         log_channels = StringRef(optarg);
>       break;
>
> Bad! This is exactly when we shouldn't be using llvm::StringRef. optarg is
> a static variable and can change if there are any arguments after "-c
> <args>".
>
> Greg
>
> On Apr 12, 2017, at 10:05 AM, Tamas Berghammer <tberghammer at google.com>
> wrote:
>
> If the process is restarted by lldb-server then "posix ptrace" should have
> some indication about it. Also "posix process" and "posix thread" can be
> useful to understand the bigger picture (all of them in lldb-server).
>
> Note: You can enable them by setting LLDB_SERVER_LOG_CHANNELS
> and LLDB_DEBUGSERVER_LOG_FILE environment variables before starting lldb.
>
> On Wed, Apr 12, 2017 at 5:11 PM Greg Clayton <clayborg at gmail.com> wrote:
>
> What is actually happening is we are stopped and handling the
> EntryBreakpoint and are in the process of trying to load all shared
> libraries, and then a signal (I am guessing) comes into the lldb-server and
> causes the target to resume. Not sure if that is due to the signal passing
> packet:
>
>
> $QPassSignals:0e;1b;20;21;22;23;24;25;26;27;28;29;2a;2b;2c;2d;2e;2f;30;31;32;33;34;35;36;37;38;39;3a;3b;3c;3d;3e;3f;40#69
>
> that gets sent these days. I will try removing this and seeing if it fixes
> anything.
>
> Is there any logging I can enabled in lldb-server to catch the resume? I
> haven't looked at the code but I finally proved what was happening last
> night (target resumes while we are stopped at a breakpoint somehow). The
> program runs and exits and when the shared libraries are finally done
> loading, there is no connection to speak to.
>
> Greg
>
> On Apr 11, 2017, at 8:26 AM, Pavel Labath <labath at google.com> wrote:
>
>
>
> On 11 April 2017 at 15:56, Greg Clayton <clayborg at gmail.com> wrote:
>
>
> On Apr 11, 2017, at 5:33 AM, Pavel Labath <labath at google.com> wrote:
>
> Are you sure this is not just an artifact of stdio buffering? I tried the
> same experiment, but I placed a real log statement, and I could see that
> all the LoadModuleAtAddress calls happen between the $T and $c packets in
> the gdb-remote packet sequence.
>
> The module loading should be synchronous, so I think the problem lies
> elsewhere.
>
> What is the nature of the breakpoint that is not getting hit? Can you
> provide a repro case? The only bug like this that I am aware of is that we
> fail to hit breakpoints in global constructors in shared libraries, but
> that hasn't worked even in 3.8..
>
>
> I unfortunately can't attach a repro case. I will be able to track this
> down, just need some pointers. I did notice that I wasn't able to hit
> breakpoints in global constructors though... Do we know why? On Mac, we get
> notified of shared libraries as they load so we never miss anything. Why
> are we not able to get the same thing with linux?
>
>
> It looks like we are intercepting the library load too late, but I haven't
> investigated yet how to fix it. It's definitely possible (this works fine
> in gdb), but I don't know how, as the dynamic linker is still a big unknown
> to me. FWIW, I think I'll be messing with the dynamic loader plugin
> soon(ish), so I'll try to fix this then.
>
> pl
>
>
>
>
>
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