[Bug tree-optimization/96826] New: missing warning appending to the result of strdup

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96826

            Bug ID: 96826
           Summary: missing warning appending to the result of strdup
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

Appending to a string created by strdup is not diagnosed by could be by looking
up the origin of the destination pointer and, if it's used in a call to a
function like strcat, or if it's accessed at an offset derived from strlen of
either the copy or the original (with no subtraction), issuing
-Wstringop-overflow.

$ cat z.c && /build/gcc-master/gcc/xgcc -B /build/gcc-master/gcc -O2 -S -Wall
z.c
void* f0 (const char *s)
{
  char *t = __builtin_strdup (s);
  __builtin_strcat (t, "xyz");      // missing warning
  return t;
}

void* f1 (const char *s)
{ 
  char *t = __builtin_strdup (s);
  t += __builtin_strlen (t);
  t[0] = 'x';
  t[1] = 'y';                       // missing warning
  t[2] = 'z';                       // ditto
  return t;
}

void* f2 (const char *s)
{ 
  char *t = __builtin_strdup (s);
  t += __builtin_strlen (t);
  __builtin_sprintf (t, "%i", 123); // missing warning
  return t;
}