[Bug c/78673] New: sprintf missing attribute nonnull on destination argument

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78673

            Bug ID: 78673
           Summary: sprintf missing attribute nonnull on destination
                    argument
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

Thew first argument of the sprintf function designates the destination into
which the function writes the formatted output followed a terminating nul
character.  Thus the argument must be a non-null pointer.  The declarations of
GCC sprintf built-ins (sprintf, vsprintf, and their checking counterparts) are
missing attribute nonnull on their first argument.  The test case below shows
that the built-ins do have the attribute on the format argument (hence the
-Wnonnull warning).  It also shows that the -Wformat-length option duplicates
the warning in the null pointer constant cases.

$ cat a.c && gcc -S -Wall -Wextra -Wpedantic a.c
void f0 (char *d)
{
  __builtin_sprintf (d, (char*)0);
}

void f1 (void)
{
  __builtin_sprintf ((char*)0, "%i", 1);   // missing warning
}

void f2 (char *d, __builtin_va_list va)
{
  __builtin_vsprintf (d, (char*)0, va);
}

void f3 (__builtin_va_list va)
{
  __builtin_vsprintf ((char*)0, "%i", va);   // missing warning
}

void f4 (char *d, unsigned n)
{
  __builtin___sprintf_chk (d, 0, n, (char*)0);
}

void f5 (unsigned n)
{
  __builtin___sprintf_chk ((char*)0, 0, n, "%i", 1);   // missing warning
}

void f6 (char *d, unsigned n, __builtin_va_list va)
{
  __builtin___vsprintf_chk (d, 0, n, (char*)0, va);
}

void f7 (unsigned n, __builtin_va_list va)
{
  __builtin___vsprintf_chk ((char*)0, 0, n, "%i", va);   // missing warning
}


a.c: In function ‘f0’:
a.c:3:3: warning: null argument where non-null required (argument 2)
[-Wnonnull]
   __builtin_sprintf (d, (char*)0);
   ^~~~~~~~~~~~~~~~~
a.c: In function ‘f2’:
a.c:13:3: warning: null argument where non-null required (argument 2)
[-Wnonnul]
   __builtin_vsprintf (d, (char*)0, va);
   ^~~~~~~~~~~~~~~~~~
a.c:13:3: warning: too many arguments for format [-Wformat-extra-args]
a.c: In function ‘f4’:
a.c:23:3: warning: null argument where non-null required (argument 4)
[-Wnonnul]
   __builtin___sprintf_chk (d, 0, n, (char*)0);
   ^~~~~~~~~~~~~~~~~~~~~~~
a.c: In function ‘f6’:
a.c:33:3: warning: null argument where non-null required (argument 4)
[-Wnonnul]
   __builtin___vsprintf_chk (d, 0, n, (char*)0, va);
   ^~~~~~~~~~~~~~~~~~~~~~~~
a.c:33:3: warning: too many arguments for format [-Wformat-extra-args]
a.c: In function ‘f0’:
a.c:1:6: warning: null format string [-Wformat-length=]
 void f0 (char *d)
      ^~
a.c: In function ‘f2’:
a.c:11:6: warning: null format string [-Wformat-length=]
 void f2 (char *d, __builtin_va_list va)
      ^~
a.c: In function ‘f4’:
a.c:21:6: warning: null format string [-Wformat-length=]
 void f4 (char *d, unsigned n)
      ^~
a.c: In function ‘f6’:
a.c:31:6: warning: null format string [-Wformat-length=]
 void f6 (char *d, unsigned n, __builtin_va_list va)
      ^~