LLDB Plugin based on cling to allow evaluation of almost all c++ expressions while debugging, overcoming most limitations of LLDB's own expression evaluation features.
WARNING This is an alpha version! Be careful and do not trust the results.
Installation
bash -c "$(wget https://raw.githubusercontent.com/tehrengruber/Defrustrator/master/scripts/install.sh -O -)"
Help
The following subcommands are supported:
include ("<file>"/<<file>>) -- Include source file
repl -- Start cling repl
print <expr> -- Print expressions return value using operator<< if possible
expression <expr> -- Evaluate expression
include_directories <dir1>, <dir2>, ... -- Add include directories
load_config <file> -- Load configuration of include directories, compile definitions, headers
load_library <file> -- Load shared library
Demo
(lldb) cling repl
(cling) #include <iostream>
(cling) std::cout << "Hello World!" << std::endl;
Hello World!
(lldb) cling include_directories /usr/include/eigen3/
(lldb) cling include <Eigen/Dense>
(lldb) cling repl
(cling) Eigen::VectorXd v(3);
(cling) v.setConstant(1);
(lldb) cling p v
1
1
1
This plugin consists of three components. A python extension handling the interaction with LLDB, some c code to be executed inside LLDB to load a shared library, and said library providing a minimal interface to send commands to the cling interpreter, which by itself is also run in the same process. Since the interpreter is run in the same process all variables can be accessed if the type and memory address is known.
include (""/<>) Include source files
(lldb) cling include <iostream>
repl Drop to cling repl
Options:
--global: Evaluate in global scope (variables of the executable are not accessible)
(lldb) cling repl
(cling) std::cout << "Hello world" << std::endl;
Hello world
print Print expressions return value using operator<< if possible
Options:
--global: Evaluate in global scope (variables of the executable are not accessible)
(lldb) run
...
-> 2 const int a = 1;
...
(lldb) cling print a
0
expression Evaluate expression
Options:
--global: Evaluate in global scope (variables of the executable are not accessible)
(lldb) cling expression int a=1;
0
include_directories <dir1>, <dir2>, ... Add include directories
(lldb) cling include_directories /usr/include/eigen3
load_library Load shared library file
(lldb) cling load_library /some/path/mylib.so
load_config Load configuration file
Include directories, compiler flags, headers, shared libraries to be included can be stored to a json file loaded when the first cling command is run.
{
"include_directories": ["/usr/include/eigen3"],
"compile_definitions": ["SOMEVAR=1"],
"headers": ["<Eigen/Dense>"],
"libraries": ["/some/path/mylib.so"]
}
__
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The line numbers reported are not correct.
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If compilation fails for some commands consecutive commands may also fail to compile even though they are correct.
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Variables declared in local scope are only accessible in that statement
(lldb) cling repl (cling) int a=1; (cling) a; input_line_12:12:3: error: use of undeclared identifier 'a' a; ^ Compilation failed -
If inclusion of a header fails since the corresponding include directory was not added beforehand reincluding the header might not work.
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In case a variable is declared and compilation fails it might not be possible to redeclare it.
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All types must be completly defined, i.e. by including the corresponding header, before they can be accessed or an error will be thrown.
Consider the following code:
struct A{}; int main() { A a; }Then trying to print A will fail as shown below:
$ lldb example (lldb) break set -n main The "cling" command has been added successfully (lldb) target create "a.out" Current executable set to 'a.out' (x86_64). (lldb) run Process 30298 launched: 'example' (x86_64) Process 30298 stopped * thread #1, name = 'a.out', stop reason = breakpoint 1.1 frame #0: 0x00000000004004b6 a.out`main at limitations_1.cpp:4 1 struct A{}; 2 int main() { 3 A a; -> 4 } (lldb) cling print a False input_line_7:4:29: error: use of undeclared identifier 'A' std::add_lvalue_reference<A>::type a = *reinterpret_cast<std::remove_reference<A>::type*>((void*)0x00007fffffffe508); ^ input_line_7:4:33: error: no type named 'type' in the global namespace std::add_lvalue_reference<A>::type a = *reinterpret_cast<std::remove_reference<A>::type*>((void*)0x00007fffffffe508); ~~^ input_line_7:4:82: error: use of undeclared identifier 'A' std::add_lvalue_reference<A>::type a = *reinterpret_cast<std::remove_reference<A>::type*>((void*)0x00007fffffffe508); ^ input_line_7:4:86: error: expected '>' std::add_lvalue_reference<A>::type a = *reinterpret_cast<std::remove_reference<A>::type*>((void*)0x00007fffffffe508); ^ > input_line_7:4:59: note: to match this '<' std::add_lvalue_reference<A>::type a = *reinterpret_cast<std::remove_reference<A>::type*>((void*)0x00007fffffffe508); ^ input_line_7:8:49: error: no type named 'print' in the global namespace Defrustrator::ValuePrinter<decltype(result)>::print(result); } ~~^ Compilation failed (lldb)
As the plugin loads the cling library into the debugged executable dynamically your executable has to be linked with libdl. In most cases appending -ldl to the compiler invocation is sufficient. Some versions of GCC though only link with a library if it is used in some sense. To force linking nonetheless alternatively add -Wl,--whole-archive -ldl to the invocation. The corresponding cmake command reads
SET(DL_LIBS_FORCE_LINK -Wl,--whole-archive ${CMAKE_DL_LIBS} -Wl,--no-whole-archive)
target_link_libraries(my_target ${DL_LIBS_FORCE_LINK})