[Bug middle-end/78138] New: missing warnings on buffer overflow with non-constant source length

["msebor at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78138

            Bug ID: 78138
           Summary: missing warnings on buffer overflow with non-constant
                    source length
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

This is just a record of a limitation addressed in a patch already posted for
review (https://gcc.gnu.org/ml/gcc-patches/2016-10/msg02308.html).

In the following program the calls to strcpy and memcpy clearly overflow, even
though the exact size of the source sequence in each case isn't known.   It
would be helpful if GCC detected this overflow and issued a warning at compile
time, rather than having the compiled program crash at runtime.

$ cat b.c && for o in "" -DCHK=1; do /build/gcc-git/gcc/xgcc -B
/build/gcc-git/gcc $o -O2 -S b.c; done
char d [5];

#ifdef CHK
#  define bos(p, t)        __builtin_object_size (d, t)
#  define memcpy(d, s, n)  __builtin___memcpy_chk (d, s, n, bos (d, 1))
#  define strcpy(d, s)     __builtin___strcpy_chk (d, s, bos (d, 1))
#else
void* memcpy (void*, const void*, unsigned long);
extern char* strcpy (char*, const char*);
#endif

void f (int i, int j)
{
  strcpy (d, j ? "12345" : "123456");
}

void g (void *p)
{
  extern unsigned n;
  if (n < 17 || 32 < n) n = 7;

  memcpy (d, p, n);
};