11.0-CURRENT -r276514: lib/libpjdlog/pjdlog.c has <stdarg.h> after <printf.h>

Mark Millard markmi at dsl-only.net
Sun Mar 22 15:46:06 UTC 2015

Dimitry Adnric wrote:

> You should be able to include standard headers (or at least, headers in
> /usr/include) in any order, and <printf.h> includes <stdio.h>, which
> then defines the correct types.

Another of the ANSI/ISO-C rules is: You must include a standard header before you refer to anything that it officially defines or declares. (The Standard C Library by P. J. Plauger, Copyright 1992, page 7, 3rd bullet under "using headers".)

Part of that status is tied to the following: In a correct ANSI/ISO-C implementation <stdio.h> defines one or more synonyms for va_list using names from the class of reserved-to-implementation names in order to declare vprintf, vfprintf, and vsprintf. But <stdio.h> does not declare va_list itself. No ANSI/ISO-C header is allowed to declare/define extra official-public-name items that are only officially from other headers. (Page 12.)

[There are also 2 more major principles for standard headers: mutual independence (so order-independence) and idempotent status (repeatability).]

Only <stdargs.h> is allowed to declare that exact name (va_list) --the synonym with the official, public name. va_list is one of many things with this private-name vs public-name synonym structure in ANSI/ISO-C.

<printf.h> is not one of the 24 (C99) or so ANSI/ISO-C standard headers (by name). Nor is __xvprintf from the C standard.

So the #include <printf> that I referenced is violating the standard by referring to something from <stdargs.h> before that header has been included.

The existing source code is in error relative to ANSI/ISO-C.

Also: Using the order

#include <stdarg.h>
#include <printf.h>

in pjdlog.c does get rid of the problem. (As it should, per the above.)

But I do not know that there is any official claim that the environment is to strictly follow ANSI/ISO-C for such points. There may be other principles instead.

How comprehensive/complete is /usr/include header analogy to the ANSI/ISO-C rules? Does FreeBSD bother with having the private-named synonyms for headers that do not official declare/define something? Is FreeBSD as explicit as ANSI/ISO-C about where official definitions are and are not in headers? (Idempotent headers are the easier part to set up. Mutual-independence gets into private-named synonym techniques in order to deal with public names being only in the official places.)

(ANSI/ISO-C does have examples of some specific things explicitly being declared/defined (public names) in more than one header: more examples where using reserved-name guard macros to gain idempotent status and order independence can be done.)

Note: Much of my background information for this and the terminology that I use is from The Standard C Library by P. J. Plauger, Copyright 1992. But I've not noticed any later ANSI/ISO material indicating the the above has changed status in more recent vintages of the standard. I could be wrong since I've not tried to be comprehensive about analyzing changes.

Mark Millard
markmi at dsl-only.net

On 2015-Mar-22, at 05:14 AM, Dimitry Andric <dim at FreeBSD.org> wrote:

On 22 Mar 2015, at 03:45, Mark Millard <markmi at dsl-only.net> wrote:
> Looking at the sources suggests that <stdarg.h> is explicitly in the #include sequence too late to guarantee va_args a definition at the point of its use in #include <printf.h> : <stdarg.h> is #include'd in pjdlog.c in the line after #include <printf.h> and printf.h itself does not (directly) include stdarg.h .
> /usr/include/printf.h (the LOOK HERE is my message editing) :
>> ...
>> #include <stdio.h>
>> #include <wchar.h>  /// <<<<< LOOK HERE for lack of <stdarg.h>
>> ...
>> int __xvprintf(FILE *fp, const char *fmt0, va_list ap);
>> ...
> /usr/srcC/lib/libpjdlog/pjdlog.c (the LOOK HERE's are my message editing) :
>> ...
>> #include <sys/cdefs.h>
>> __FBSDID("$FreeBSD: head/lib/libpjdlog/pjdlog.c 258791 2013-12-01 09:41:06Z pjd $");
>> #include <sys/types.h>
>> #include <sys/socket.h>
>> #include <sys/un.h>
>> #include <netinet/in.h>
>> #include <arpa/inet.h>
>> #include <assert.h>
>> #include <errno.h>
>> #include <libutil.h>
>> #include <limits.h>
>> #include <printf.h>  /// <<<<< LOOK HERE
>> #include <stdarg.h>  /// <<<<< LOOK HERE for stdarg.h vs. printf.h order

You should be able to include standard headers (or at least, headers in
/usr/include) in any order, and <printf.h> includes <stdio.h>, which
then defines the correct types.

However, there is a problem in the gcc ports.  What happens, is that the
gcc port uses its *own* munged versions of stdio.h and stdarg.h, and
includes them instead of the system versions.  For example, the gcc 4.7
port has this "fixed" version of stdio.h:


which explicitly *disables* our declaration of __va_list (the type which
va_list is based on):

 typedef __va_list __not_va_list__;

For functions like vprintf(), it replaces __va_list by a GNU builtin
variant, for example:

 int      vprintf(const char * __restrict, __gnuc_va_list);

However, it does not properly declare the regular va_list type, and then
things break in interesting ways.

I think the ports should not attempt to "fix" our include files.


More information about the freebsd-current mailing list