[Rd] custom allocators, Valgrind and uninitialized memory

[Andreas Kersting]

Hi,

In my package bettermc, I use a custom allocator, which hands out already defined/initialized memory (mmap of a POSIX shared memory object).

If my code is run in R which was configured --with-valgrind-instrumentation > 0, Valgrind will (correctly) complain about uninitialized memory being used, e.g.

==813836== Conditional jump or move depends on uninitialised value(s)
==813836==    at 0x4F0A9D: getvar (svn/R-devel/src/main/eval.c:5171)
==813836==    by 0x4D9B38: bcEval (svn/R-devel/src/main/eval.c:6867)
==813836==    by 0x4F0077: Rf_eval (svn/R-devel/src/main/eval.c:727)
==813836==    by 0x4F09AF: forcePromise (svn/R-devel/src/main/eval.c:555)
==813836==    by 0x4F0C57: FORCE_PROMISE (svn/R-devel/src/main/eval.c:5136)
==813836==    by 0x4F0C57: getvar (svn/R-devel/src/main/eval.c:5177)
==813836==    by 0x4D9B38: bcEval (svn/R-devel/src/main/eval.c:6867)
==813836==    by 0x4F0077: Rf_eval (svn/R-devel/src/main/eval.c:727)
==813836==    by 0x4F1A8D: R_execClosure (svn/R-devel/src/main/eval.c:1897)
==813836==    by 0x4F2783: Rf_applyClosure (svn/R-devel/src/main/eval.c:1823)
==813836==    by 0x4DF61D: bcEval (svn/R-devel/src/main/eval.c:7083)
==813836==    by 0x4F0077: Rf_eval (svn/R-devel/src/main/eval.c:727)
==813836==    by 0x4F1A8D: R_execClosure (svn/R-devel/src/main/eval.c:1897)
==813836==  Uninitialised value was created by a client request
==813836==    at 0x52D5CF: Rf_allocVector3 (svn/R-devel/src/main/memory.c:2892)
==813836==    by 0x16B415EA: allocate_from_shm (packages/tests-vg/bettermc/src/copy2shm.c:289)
==813836==    by 0x49D123: R_doDotCall (svn/R-devel/src/main/dotcode.c:614)
==813836==    by 0x4DA36D: bcEval (svn/R-devel/src/main/eval.c:7671)
==813836==    by 0x4F0077: Rf_eval (svn/R-devel/src/main/eval.c:727)
==813836==    by 0x4F1A8D: R_execClosure (svn/R-devel/src/main/eval.c:1897)
==813836==    by 0x4F2783: Rf_applyClosure (svn/R-devel/src/main/eval.c:1823)
==813836==    by 0x4F0243: Rf_eval (svn/R-devel/src/main/eval.c:850)
==813836==    by 0x49B68F: do_External (svn/R-devel/src/main/dotcode.c:573)
==813836==    by 0x4D3566: bcEval (svn/R-devel/src/main/eval.c:7115)
==813836==    by 0x4F0077: Rf_eval (svn/R-devel/src/main/eval.c:727)
==813836==    by 0x4F1A8D: R_execClosure (svn/R-devel/src/main/eval.c:1897)

(allocate_from_shm() is my function calling allocVector3() with a custom allocator.) Valgrind is correct, because allocVector3() explicitly calls VALGRIND_MAKE_MEM_UNDEFINED() on the memory my custom allocator returns.

- Sould allocVector3() call VALGRIND_MAKE_MEM_UNDEFINED() also if a custom allocator is used? For some custom allocators this is correct, for others not.

- Or should the code using a custom allocator call VALGRIND_MAKE_MEM_DEFINED() on the DATAPTR() returned by allocVector3()? E.g.

...
ret = PROTECT(allocVector3(asInteger(type), asReal(length), &allocator));
VALGRIND_MAKE_MEM_DEFINED(DATAPTR(ret), size);
...

For the latter to work also on systems without Valgrind installed, I need to include both valgrind.h and memcheck.h in the src of my package and include these (rather than the system headers), correct? Should I best take these headers directly from R (src/include/vg)?

Thanks! Regards,
Andreas