LLDB fails to load C++ Plugin (sharedlib) - error: this file does not represent a loadable dylib

Hello Everyone,

I started looking into the LLDB with the intention of adding custom commands for my SW debugging purpose. For a better Understanding let me explain what I intend to do. I have an source file generated automatically from a Model with certain anotations added as comments in the code. This code will would be compiled and in error cases debugged. When debugging I may have to set breakpoints at certain statements in the code based on the anotations incerted by the code generator. This is done by specifying the source file and the line number. I Use CLANG to get the line number and source file for the comments.

I would like to have custom commands for this and internally map the to already existing commands e.g. "breakpoint set -f -l". I found some examples for python, and for c++ I only found the example "lldb/examples/plugins/commands/fooplugin.cpp" for writing C++ plugin (dynLib) shipped with the LLDB source. In this example adding a new commands was straight forward and in the DoExecute function, I call the interpreter to handle a breakpoint command. I intend to use C++ rather than Python.

This works fine for a simple shared lib (Simple modification of the Example provided in LLDB. In Do execute call interpreter to handle a breakpoint command). However if I add other C++ sources which does XML parsing, CLANG RecursiveASTVisitor etc to the Library, creating the shared library with eclipse is sucessful. I can link the created library to an application and it works well. However when I load this in lldb with the command ==> plugin load "/home/bkebianyor/eclipse-workspace/Model_LLDB_Debugger/Debug/libModel_LLDB_Debugger.so", I get the error message: "error: this file does not represent a loadable dylib".

#Loading the shared lib that is linked just to the liblldb.so - SUCESSFUL
(lldb)
(lldb) plugin load /home/bkebianyor/eclipse-workspace/DynLib/Debug/libDynLib.so
(lldb)

#Loading the shared lib that is linked just to the liblldb.so + libxerces-c-3.2.so - FAILS

(lldb) plugin load "/home/bkebianyor/eclipse-workspace/Model_LLDB_Debugger/Debug/libModel_LLDB_Debugger.so"
error: this file does not represent a loadable dylib

I have searched for this error on google, but could not find out how to resolve this error. Most answers pointed to a mismatch of the lldb version in the shared lib to be loaded and that linked to lldb, but that is not my case. I am using lldb-5.0.2 and LLVM/CLANG 5.0.2 toolcahin on Linux 16.04.1-Ubuntu and Eclipse IDE. LLVM was built with SHARED_LIBS set to ON.

Would be grateful for an answer.

Thanks and Regards,

Bewoayia

-------------
Dipl.- Ing. Bewoayia Kebianyor
Researcher - Hardware/Software Design Methodology Group

OFFIS e.V. - Institut für Informatik
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I would expect the issue is that dlopen fails to locate the dependent
libraries of your plugin. Can you lookup the actual dlopen call which
opens your library and see what is the exact error it fails with?

Also try running
ldd /home/bkebianyor/eclipse-workspace/Model_LLDB_Debugger/Debug/libModel_LLDB_Debugger.so

That will list dependencies that the loader can and cannot resolve.

A possible alternative to a plugin could be to use "breakpoint set -p", which does a regular expression match on the source, so you can set a breakpoint based on the text of an annotation. You could wrap this in a python script if you want to make it into a custom command.

Ted

Comments inlined below.

Hello Everyone,

I started looking into the LLDB with the intention of adding custom commands for my SW debugging purpose. For a better Understanding let me explain what I intend to do. I have an source file generated automatically from a Model with certain anotations added as comments in the code. This code will would be compiled and in error cases debugged. When debugging I may have to set breakpoints at certain statements in the code based on the anotations incerted by the code generator. This is done by specifying the source file and the line number. I Use CLANG to get the line number and source file for the comments.

Did you know we have the ability to set breakpoints using source regular expression?

(lldb) breakpoint set --source-pattern-regexp “// breakpoint [0-9]+” --file /path/to/foo.cpp

This will use a regular expression to search the source file for the regular expression you specify and have one breakpoint that has multiple locations.

I would like to have custom commands for this and internally map the to already existing commands e.g. "breakpoint set -f -l". I found some examples for python, and for c++ I only found the example "lldb/examples/plugins/commands/fooplugin.cpp" for writing C++ plugin (dynLib) shipped with the LLDB source. In this example adding a new commands was straight forward and in the DoExecute function, I call the interpreter to handle a breakpoint command. I intend to use C++ rather than Python.

Do you even need this custom command given what I said above?

This works fine for a simple shared lib (Simple modification of the Example provided in LLDB. In Do execute call interpreter to handle a breakpoint command). However if I add other C++ sources which does XML parsing, CLANG RecursiveASTVisitor etc to the Library, creating the shared library with eclipse is sucessful. I can link the created library to an application and it works well. However when I load this in lldb with the command ==> plugin load "/home/bkebianyor/eclipse-workspace/Model_LLDB_Debugger/Debug/libModel_LLDB_Debugger.so", I get the error message: "error: this file does not represent a loadable dylib".

#Loading the shared lib that is linked just to the liblldb.so - SUCESSFUL
(lldb)
(lldb) plugin load /home/bkebianyor/eclipse-workspace/DynLib/Debug/libDynLib.so
(lldb)

#Loading the shared lib that is linked just to the liblldb.so + libxerces-c-3.2.so - FAILS

(lldb) plugin load "/home/bkebianyor/eclipse-workspace/Model_LLDB_Debugger/Debug/libModel_LLDB_Debugger.so"
error: this file does not represent a loadable dylib

I have searched for this error on google, but could not find out how to resolve this error. Most answers pointed to a mismatch of the lldb version in the shared lib to be loaded and that linked to lldb, but that is not my case. I am using lldb-5.0.2 and LLVM/CLANG 5.0.2 toolcahin on Linux 16.04.1-Ubuntu and Eclipse IDE. LLVM was built with SHARED_LIBS set to ON.

I am guessing that maybe your libModel_LLDB_Debugger.so shared library can’t find all the dependencies it requires when being loaded. Try making a small a.out file that links against this library and try to run your a.out program. See if you see any errors when the a.out tries to launch.

Greg

Hello,

Thanks to Ted, Pavel and Greg for your reply with suggestion on how to resolve the issue. Greg's comment below help me to resolve the issue.

I am guessing that maybe your libModel_LLDB_Debugger.so shared
library can't find all the dependencies it requires when being
loaded. Try making a small a.out file that links against this library
and try to run your a.out program. See if you see any errors when the
a.out tries to launch.

While I already had an executable linking to the library, I didnot call functions referencing to Clang and XML parsing from the libModel_LLDB_Debugger.so. I simple called a function to print out the size of a map container I have within my lib. Which worked fine. Based on Greg's comment, I then extended this to call more functions which does the XML parsing and AST Parsing, then linking failed with error: undefined reference to `typeinfo for clang::ASTConsumer'. I searched on google and found out that this error has to do with the fact that LLVM and Clang are compiled with -fno-rtti by default and I am not explicitly setting the compile flag -fno-rtti in my project. I then added this to the "ASTConsumer derived class" in my project and it resolved the issue.

Thanks once more.

Thanks and Regards,

Bewoayia