[sdcc-devel] [ sdcc-Bugs-1932509 ] broken offsetof() handling in SDCCast.c

[SourceForge.net <no...@so...>]

Bugs item #1932509, was opened at 2008-04-02 20:20
Message generated for change (Tracker Item Submitted) made by Item Submitter
You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=100599&aid=1932509&group_id=599

Please note that this message will contain a full copy of the comment thread,
including the initial issue submission, for this request,
not just the latest update.
Category: C-Front End
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: Robert Larice (rlar)
Assigned to: Nobody/Anonymous (nobody)
Summary: broken offsetof() handling in SDCCast.c

Initial Comment:
struct st {
  char a;
};

char * buggy(){
  return &(((struct st code *) 0x1234) -> a);
}

returns an incorrect generic pointer at least for
  mcs51 target.

the problem is caused by a special handling of
  cast's resembling the above one,
in file SDCCast.c:3961

this special handling was built-in to process
the the following macro (comment from SDCCast.c)

/* handle offsetof macro:            */
/* #define offsetof(TYPE, MEMBER) \  */
/* ((unsigned) &((TYPE *)0)->MEMBER) */

which in my opinion is naive anyway.
offsets are better calculated by substraction of pointers, something very remotly like:
#define offsetof(TYPE, MEMBER) \
  (((int) &((TYPE*)0)->MEMBER) - (int) &(TYPE*)0)

i've attached a testcase for support/regression...
  (tested only for mcs51-small)
the testcase successfully destinguishes sdcc
from a modified sdcc with disabled SDCCast.c:3961

Robert Larice


----------------------------------------------------------------------

You can respond by visiting: 
https://sourceforge.net/tracker/?func=detail&atid=100599&aid=1932509&group_id=599