How to debug Clang plugin using lldb (or gdb)

Question

I want to debug Clang plugin.
However, I can't find informations about debugging of Clang plugin.
If you know how to debug Clang plugin, Could you tell me that information? thanks.

Answer 1

Just a small outline as i'm trying this myself atm. I am using lldb.

I am currently able to stop at any given function in the plugin but the source code is missing. It only shows the assembly.

When you invoke clang with -Xclang -plugin (...) it will fork into a child process. When invoking your plugin pass also the -v option to see the child process command line. Then use this command line in the debugger.

Original command line:

$> clang++ -Xclang -load -Xclang ${PLUGIN} -Xclang -plugin -Xclang cgd -std=c++11 -w -fsyntax-only -v

should output:

clang version 3.1 (tags/RELEASE_31/final 163510)
Target: x86_64-unknown-linux-gnu
Thread model: posix
 "/srv/scratch/sigubufo/clang/stable/3.1_src/build/bin/clang-3.1" -cc1 -triple x86_64-unknown-linux-gnu -fsyntax-only -disable-free -main-file-name call_in_if.cpp -mrelocation-model static -mdisable-fp-elim -masm-verbose -mconstructor-aliases -munwind-tables -target-cpu x86-64 -momit-leaf-frame-pointer -v -resource-dir /srv/scratch/sigubufo/clang/stable/3.1_src/build/bin/../lib/clang/3.1
-fmodule-cache-path /var/tmp/clang-module-cache -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../include/c++/4.6
-internal-isystem /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../include/c++/4.6/x86_64-linux-gnu
-internal-isystem /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../include/c++/4.6/backward
-internal-isystem /usr/local/include -internal-isystem /srv/scratch/sigubufo/clang/stable/3.1_src/build/bin/../lib/clang/3.1/include
-internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -Werror -w -std=c++11 -fdeprecated-macro
-fdebug-compilation-dir /srv/scratch/sigubufo/danceos_wd/clang/qtcreator-build -ferror-limit
19 -fmessage-length 205 -mstackrealign -fgnu-runtime
-fobjc-runtime-has-arc -fobjc-runtime-has-weak -fobjc-fragile-abi -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -load lib/CallGraphDumper.so -plugin cgd -x c++ ../test_cases/call_in_if.cpp
clang -cc1 version 3.1 based upon LLVM 3.1svn default target x86_64-unknown-linux-gnu
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../include/c++/4.6
 /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../include/c++/4.6/x86_64-linux-gnu
 /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../include/c++/4.6/backward
 /usr/local/include
 /srv/scratch/sigubufo/clang/stable/3.1_src/build/bin/../lib/clang/3.1/include
 /usr/include/x86_64-linux-gnu
 /usr/include
End of search list.

This is the part you need:

"/srv/scratch/sigubufo/clang/stable/3.1_src/build/bin/clang-3.1" -cc1 -triple x86_64-unknown-linux-gnu -fsyntax-only -disable-free -main-file-name call_in_if.cpp -mrelocation-model static -mdisable-fp-elim -masm-verbose -mconstructor-aliases -munwind-tables -target-cpu x86-64 -momit-leaf-frame-pointer -v -resource-dir /srv/scratch/sigubufo/clang/stable/3.1_src/build/bin/../lib/clang/3.1 -fmodule-cache-path /var/tmp/clang-module-cache -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../include/c++/4.6 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../include/c++/4.6/x86_64-linux-gnu -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../include/c++/4.6/backward -internal-isystem /usr/local/include -internal-isystem /srv/scratch/sigubufo/clang/stable/3.1_src/build/bin/../lib/clang/3.1/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -Werror -w -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /srv/scratch/sigubufo/danceos_wd/clang/qtcreator-build -ferror-limit 19 -fmessage-length 205 -mstackrealign -fgnu-runtime -fobjc-runtime-has-arc -fobjc-runtime-has-weak -fobjc-fragile-abi -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -load lib/CallGraphDumper.so -plugin cgd -x c++ ../test_cases/call_in_if.cpp

Now you invoke lldb with:

lldb "/srv/scratch/sigubufo/clang/stable/3.1_src/build/bin/clang-3.1"

And then in the lldb prompt you do

(lldb) break set --name YourPlugin::FunctionToBreakAt

(lldb) process launch -- -cc1 -triple x86_64-unknown-linux-gnu -fsyntax-only -disable-free -main-file-name call_in_if.cpp -mrelocation-model static -mdisable-fp-elim -masm-verbose -mconstructor-aliases -munwind-tables -target-cpu x86-64 -momit-leaf-frame-pointer -v -resource-dir /srv/scratch/sigubufo/clang/stable/3.1_src/build/bin/../lib/clang/3.1 -fmodule-cache-path /var/tmp/clang-module-cache -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../include/c++/4.6 -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../include/c++/4.6/x86_64-linux-gnu -internal-isystem /usr/lib/gcc/x86_64-linux-gnu/4.6/../../../../include/c++/4.6/backward -internal-isystem /usr/local/include -internal-isystem /srv/scratch/sigubufo/clang/stable/3.1_src/build/bin/../lib/clang/3.1/include -internal-externc-isystem /usr/include/x86_64-linux-gnu -internal-externc-isystem /include -internal-externc-isystem /usr/include -Werror -w -std=c++11 -fdeprecated-macro -fdebug-compilation-dir /srv/scratch/sigubufo/danceos_wd/clang/qtcreator-build -ferror-limit 19 -fmessage-length 205 -mstackrealign -fgnu-runtime -fobjc-runtime-has-arc -fobjc-runtime-has-weak -fobjc-fragile-abi -fcxx-exceptions -fexceptions -fdiagnostics-show-option -fcolor-diagnostics -load lib/CallGraphDumper.so -plugin cgd -x c++ ../test_cases/call_in_if.cpp

And that should work.