[lldb-dev] Using LLDB C++ API for automated debugging sessions

[Jim Ingham via lldb-dev]

The main problem with trying to run a debug session multithreaded is coordinating execution control.  Thread A gets a variable list and iterates over it to get child values.  Thread B issues a "step" command.  The API's thread A calls will either fail (because the target is running) or maybe fetch data that is now one step too new for some of the calls, if the step completed quickly.  LLDB doesn't have any built-in mechanism for a thread to start a session which locks out other threads from running the target.  So if you want to do your work on multiple threads you'll need to add something like that.  And as Greg says, for many purposes you will need to have a cancellation mechanism as well, since people often want to "step really quickly" and don't want to wait for fresh values of the local variables to be fetched before the next step can start.

Jim
 

> On Jul 18, 2019, at 4:00 AM, Jayvee Neumann via lldb-dev <lldb-dev at lists.llvm.org> wrote:
> 
> Thank you for your help.
> 
> What is the reason for using SBLaunchInfo over calling tgt.Launch with the launch configuration as a set of parameters? Furthermore I do not see a way to set stdout, stdin, and stderr for the launched process by using SBLaunchInfo.
> 
> I have a question regarding the event loop.
> Is lldb thread-safe enough such that I can run that loop in another std::thread while simultaneously using other debugger functions?
> 
> Kind regards,
> Jayvee
> 
> Am Fr., 12. Juli 2019 um 19:56 Uhr schrieb Greg Clayton <clayborg at gmail.com>:
> You need to call SBDebugger::Initialize() before calling SBDebugger::Create().
> 
> Also, please use the SBLaunchInfo method for launching if possible where you create a SBLaunchInfo, then call tgt.Launch() with the instance.
> 
> Other than that, as Jim said, you need to setup an event loop if you don't use synchronous mode where you wait for events and respond to events. 
> 
> Greg
> 
>> On Jun 26, 2019, at 4:58 AM, Jayvee Neumann via lldb-dev <lldb-dev at lists.llvm.org> wrote:
>> 
>> Dear LLDB developers,
>> 
>> I am currently stuck while using the C++ API of LLDB. I am unable to correctly launch a process.
>> The code I have written looks as follows:
>> 
>> int main(int argc, char *argv[]){
>> LLDBSentry senty;
>> SBDebugger dbg(SBDebugger::Create());
>> ...
>> const char *exeFilePath = "./target";
>> const char *arch = "x86_64";
>> const char *platform = "";
>> const char *dependentLibs = "";	
>> SBError error;
>> SBTarget tgt = dbg.CreateTarget(exeFilePath, arch, platform, dependentLibs, error);
>> ...
>> SBListener listen;
>> SBProcess proc = tgt.Launch(
>> listen,
>> nullptr,
>> nullptr,
>> nullptr,
>> "targetout.txt",
>> nullptr,
>> "./",
>> eLaunchFlagExec | eLaunchFlagDebug,
>> false,
>> error
>> );
>> ...
>> SBThread thread = proc.GetSelectedThread(); // (1)
>> ...
>> }
>> 
>> The complete code (usr.cpp) is added as an attachment to this email.
>> Its output is also added as a text file (stdout.txt) to this email.
>> 
>> The problem I have is, that thread.IsValid() returns null after line (1). Furthermore, the process says, that its state is eStateStopped, when asked via proc.IsStopped() it answers "false", however.
>> The debugging target is a simple file that writes a hexadecimal number every 10us to stdout. I can see that the target is running, because targetout.txt is growing in size and its content is valid output from "target".
>> Can you tell me what my mistake is?
>> 
>> Kind Regards
>> Jayvee
>> 
>> <usr.cpp><stdout.txt>_______________________________________________
>> lldb-dev mailing list
>> lldb-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/lldb-dev
> 
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