[Rd] [External] Re: use of the tcltk package crashes R 4.0.1 for Windows

[peter dalgaard]

> On 7 Jun 2020, at 18:59 , Jeroen Ooms <jeroenooms using gmail.com> wrote:
> 
> On Sun, Jun 7, 2020 at 5:53 PM <luke-tierney using 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

But that section #defines calloc and free to Rm_... counterparts in lockstep? (I assume that is where dlmalloc comes in?)

Anyways, does it actually work to change free() to Free()? If so, then all this post mortem analysis is rather a moot point.

-pd

-- 
Peter Dalgaard, Professor,
Center for Statistics, Copenhagen Business School
Solbjerg Plads 3, 2000 Frederiksberg, Denmark
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Office: A 4.23
Email: pd.mes using cbs.dk  Priv: PDalgd using gmail.com