debugging gcc compiled code with lldb does not work for every dbg_* function

[aryoda]

Running lldb with

R -d lldb

and setting a breakpoint (same commands as in gdb so far) prints strange results:

(lldb) p dbg_print(x)
error: warning: '__cplusplus' macro redefined
previous definition is here
warning: '__GNUC__' macro redefined
previous definition is here
...
warning: '__LDBL_EPSILON__' macro redefined
previous definition is here
warning: '__LDBL_DENORM_MIN__' macro redefined
previous definition is here
error: Couldn't lookup symbols:
  Rcpp::PreserveStorage<Rcpp::Vector<4> >::~PreserveStorage()
  Rcpp::Vector<4>::Vector(Rcpp::Vector<4> const&)

but SEXP printing does work:

(lldb) p dbg_print(x.data)
[1] "foo"   "bar"   NA      "hello"

Investigate this (low prio)...

See also:
Is it possible to debug a gcc-compiled program using lldb, or debug a clang-compiled program using gdb?

[aryoda]

Perhaps switching to clang++ solves the problem, see:

http://r-pkgs.had.co.nz/src.html

Use clang instead of gcc to compile your C++ code: it gives much better error messages. You can make clang the default by creating a .R/Makevars (linux and mac) or .R/Makevars.win (windows) file in your home directory that contains:
CXX=clang++

But a first try with a clean & rebuild of CppDebugHelper only (not Rcpp) didn't help (debugging/stepping works, but printing not):

(lldb) p dbg_print(x)
error: CppDebugHelper.so DWARF DIE at 0x00099d2f (class String) has a member variable 0x00099d44 (buffer) whose type is a forward declaration, not a complete definition.
Try compiling the source file with -fstandalone-debug
error: Couldn't lookup symbols:
  Rcpp::Vector<16>::Vector(Rcpp::Vector<16> const&)
  Rcpp::traits::proxy_cache<16>::~proxy_cache()
  Rcpp::PreserveStorage<Rcpp::Vector<16> >::~PreserveStorage()

Some interesting links:

• https://stackoverflow.com/questions/20875924/can-clang-compile-code-with-gcc-compiled-a-libs
• https://stackoverflow.com/a/35634323
• http://lists.r-forge.r-project.org/pipermail/rcpp-devel/2012-August/004208.html
• https://stackoverflow.com/a/25266566

It seems that R and Rcpp must be recompiled completely with clang++ (but clang++ seems to be supported by R only on OSX/Mac) to avoid mixing compilers...

in general you CANNOT mix C++ code from different compilers

[aryoda]

This Debugging compiled code in R with lldb video by Jim Hester show the lldb does work within RStudio (on OSX/Mac)

It also gives good "how to debug" instructions via a live debugging session in RStudio

Direct link to the video: https://www.youtube.com/watch?v=R3-IMGyNJY4