h/t Tim Taylor for pointing out my blindspot :) We have Memcpy() in API already [1], which wraps a 0-aware R_chk_memcpy() [2].
We don't quite have Memset() in API, though; instead we have Memzero() [3] for R_chk_memset(s, 0, n) which is 0-aware memset() [4]. [1] https://github.com/r-devel/r-svn/blob/9e597ca8132e8b6298b0bedb39fa8deba5c819df/src/include/R_ext/RS.h#L59-L60 [2] https://github.com/r-devel/r-svn/blob/9e597ca8132e8b6298b0bedb39fa8deba5c819df/src/main/memory.c#L3575-L3580 [3] https://github.com/r-devel/r-svn/blob/9e597ca8132e8b6298b0bedb39fa8deba5c819df/src/include/R_ext/RS.h#L62-L63 [4] https://github.com/r-devel/r-svn/blob/9e597ca8132e8b6298b0bedb39fa8deba5c819df/src/main/memory.c#L3582-L3587 Mike C On Wed, Apr 23, 2025 at 8:57 AM Michael Chirico <michaelchiri...@gmail.com> wrote: > > From R 4.5.0 [1], all builds of R discourage use of INTEGER() [and > friends REAL(), ... and *_RO() equivalents] on length-0 SEXP [2]. > Before R 4.5.0, this was the behavior under --enable-strict-barrier. > > That means the following can segfault under strict builds (e.g. > -fsanitize=alignment and -O0): > > SEXP x = PROTECT(Rf_allocVector(INTSXP, 0)); > SEXP y = PROTECT(Rf_allocVector(INTSXP, 0)); > const int *x = INTEGER_RO(x); // invalid! > int *y = INTEGER(y); > memcpy(y, x, 0); // alluring, but undefined behavior! > > There are a number of CRAN packages that fall victim to this, see e.g. > this PR and others linked to it [3]. I'm sure there are dozens if not > hundreds of other equivalent bugs waiting to be discovered that just > aren't covered by existing tests. > > {rlang} took the approach to define r_memcpy() and r_memset() which > wrap memcpy() and memset(), resp., with an added length-0 check [4]; I > think R itself should offer these (probably more consistently styled > as R_Memcpy() and R_Memset()). > > (NB there's a possibility I'm still not fully grasping what's going on here > :) ) > > Mike C > > [1] related: https://stat.ethz.ch/pipermail/r-devel/2024-June/083456.html > [2] > https://github.com/r-devel/r-svn/blob/2b29e52e1c4e3d26b649cb7ac320b8a3dd13de30/src/main/memory.c#L4146 > [3] https://github.com/r-lib/vctrs/pull/1968 > [4] https://github.com/r-lib/rlang/pull/1797 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
