[External] Re: use of the tcltk package crashes R 4.0.1 for Windows
On Sun, Jun 7, 2020 at 5:53 PM <luke-tierney at uiowa.edu> wrote:
On Sun, 7 Jun 2020, peter dalgaard wrote:
So this wasn't tested for a month?
Anyways, Free() is just free() with a check that we're not freeing a null pointer, followed by setting the pointer to NULL. At that point of tcltk.c, we have
for (objc = i = 0; i < length(avec); i++){
const char *s;
char *tmp;
if (!isNull(nm) && strlen(s = translateChar(STRING_ELT(nm, i)))){
// tmp = calloc(strlen(s)+2, sizeof(char));
tmp = Calloc(strlen(s)+2, char);
*tmp = '-';
strcpy(tmp+1, s);
objv[objc++] = Tcl_NewStringObj(tmp, -1);
free(tmp);
}
if (!isNull(t = VECTOR_ELT(avec, i)))
objv[objc++] = (Tcl_Obj *) R_ExternalPtrAddr(t);
}
and I can't see how tmp can be NULL at the free(), nor can I see it mattering if it is not set to NULL (notice that it goes out of scope with the for loop).
Right. And the calloc->Calloc change doesn't look like an issue either -- just checking for a NULL. If the crash is happening in free() then that most likely means corrupted malloc data structures. Unfortunately that could be happening anywhere.
Writing R extensions, section 6.1.2 says: "Do not assume that memory allocated by Calloc/Realloc comes from the same pool as used by malloc: in particular do not use free or strdup with it." I think the reason is that R uses dlmalloc for Calloc on Windows: https://github.com/wch/r-source/blob/c634fec5214e73747b44d7c0e6f047fefe44667d/src/main/memory.c#L94-L103