[Rd] another fix for R crashes under enable-strict-barrier, lto, trunk at 72156

[Martin Maechler]

>>>>> Hin-Tak Leung <htl10 at users.sourceforge.net>
>>>>>     on Sat, 11 Feb 2017 19:30:26 +0000 writes:

    > I haven' t touched R for some 18 months, and so I have no
    > idea if this is a recent problems or not; but it certainly
    > did not segfault two years ago.  Since it has been
    > crashing (segfault) under 'make check-all' for over a
    > month, I reckon I'll have to look at it myself, to have it
    > fixed.

    > I have been having the ' --enable-memory-profiling --enable-strict-barrier --with-valgrind-instrumentation=2" options

    > for perhaps a decade - because I work(ed) with people who
    > like to write buggy code :-(. And I also run 'make
    > check-all' from time to time until two years ago.

    > ./configure --enable-memory-profiling --enable-strict-barrier --enable-byte-compiled-packages --with-valgrind-instrumentation=2 --enable-lto

    > current R dev crashes in make check-all . The fix is this:


    > --- a/src/main/memory.c
    > +++ b/src/main/memory.c
    > @@ -3444,7 +3444,7 @@ R_xlen_t (XTRUELENGTH)(SEXP x) { return XTRUELENGTH(CHK2(x)); }
    >  int  (IS_LONG_VEC)(SEXP x) { return IS_LONG_VEC(CHK2(x)); }

    >  const char *(R_CHAR)(SEXP x) {
    > -    if(TYPEOF(x) != CHARSXP)
    > +    if(x && (TYPEOF(x) != CHARSXP))
    >         error("%s() can only be applied to a '%s', not a '%s'",
    >               "CHAR", "CHARSXP", type2char(TYPEOF(x)));
    >      return (const char *)CHAR(x);


    > It is a fairly obvious fix to a bug since

    > include/Rinternals.h:#define TYPEOF(x) ((x)->sxpinfo.type)

    > and it was trying to de-reference "0->sxpinfo.type" (under
    > --enable-strict-barrier I think).

Thank you  Hin-Tak!

I did not yet try to reproduce the segfault, and I am not
the expert here.  Just some remarks and a follow up question:

Typically, the above R_CHAR() is equivalent to the  CHAR()
macro which is used in many places.  I  _think_ that the bug is
that this is called with '0' instead of a proper SEXP  in your
case and the bug fix may be more appropriate "up stream", i.e.,
at the place where that call happens  rather than inside
R_CHAR.

Any chance you saw or can get more info about the location of
the crash, such as a stack trace ? 

The idiom     if(TYPEOF(x)  ==  <some>SXP)
is used in many places in the R sources, and I think we never
prepend that with a  'x && '  like you propose above.




    > So there.

    > While I subscribe to R-devel, I switched off delivery, so
    > please CC if a response is required.