source: trunk/doc/lossage @ 8769

This file describes cases where platforms we care about do not
correctly implement the ANSI C and POSIX specifications.  The cases
described are:

        setsid() and Ultrix 4.2
        getpgrp() and Ultrix, SunOS 4.x
        Pseudo-ttys and Ultrix 4.2
        strerror() and SunOS

setsid() and Ultrix 4.2
-----------------------

Under Ultrix 4.2, setsid() does not dissociate a process from its
controlling tty.

For a program using imake, an appropriate way to detect the problem
is:

        #define HAVE_SETSID
        #ifdef ultrix
        /* Under Ultrix 4.2, setsid() doesn't dissociate the calling process
         * from its controlling tty.  Use setpgid() and the TIOCNOTTY
         * ioctl instead. */
        #undef HAVE_SETSID
        #endif

For a program using Autoconf, you should put the following test in
your aclocal.m4:

        AC_DEFUN(ATHENA_FUNC_SETSID,
        [AC_MSG_CHECKING(for working setsid)
        AC_CACHE_VAL(athena_cv_func_setsid,
        [AC_TRY_RUN([
        #include <sys/types.h>
        #include <sys/stat.h>
        #include <fcntl.h>
        #include <unistd.h>
        int main()
        {
            setsid();
            return (open("/dev/tty", O_RDWR, 0666) < 0) ? 0 : 1;
        }
        ], athena_cv_func_setsid=yes, athena_cv_func_setsid=no,
           athena_cv_func_setsid=no)])dnl
        AC_MSG_RESULT($athena_cv_func_regcomp)
        if test $athena_cv_func_regcomp = yes; then
          AC_DEFINE(HAVE_SETSID)
        fi])

and then put ATHENA_FUNC_SETSID in your configure.in.

In either case, an appropriate workaround is:

        #ifndef HAVE_SETSID
        #include <sys/ioctl.h>
        static int bsd_emulate_setsid()
        {
            int fd, status;

            status = setpgid(getpid(), getpid());
            if (status < 0)
                return status;
            fd = open("/dev/tty", O_RDWR, 0666);
            if (fd >= 0) {
                status = ioctl(fd, TIOCNOTTY, (char *) 0);
                close(fd);
            }
            return status;
        }
        #define setsid bsd_emulate_setsid
        #endif

getpgrp() and Ultrix, SunOS 4.x
-------------------------------

The BSD 4.3 getpgrp() interface takes a process ID argument indicating
which process one wants the process group of.  POSIX "simplified" the
getpgrp() interface by eliminating the argument and assuming the
calling process's ID.  Ultrix and SunOS both have "POSIX" or "System
V" environments which have the correct getpgrp() interface, but we
don't use those environments.

For a program using imake, an appropriate way to detect the problem
is:

        #define GETPGRP_VOID
        #if defined(ultrix) || (defined(sun) && !defined(__svr4__))
        /* Ultrix 4.2 and SunOS 4.1.3_U1 use the old BSD interface for
         * getpgrp(), which takes an argument.  Use the BSD getpgrp()
         * interface instead of the POSIX interface. */
        #undef GETPGRP_VOID
        #endif

For a program which uses Autoconf, put AC_FUNC_GETPGRP in your
configure.in file.

In either case, an appropriate workaround is:

        #ifndef GETPGRP_VOID
        #include <sys/types.h>
        static pid_t bsd_emulate_getpgrp()
        {
            return getpgrp(getpid());
        }
        #define getpgrp bsd_emulate_getpgrp
        #endif

Pseudo-ttys and Ultrix 4.2
--------------------------

Opening a slave pty under Ultrix without opening the parent causes the
pty to become unusable until a reboot.  The best workaround is to
always open the parent side of pseudo-ttys first.  See the section on
pseudo-ttys in the "nonstd" file in this directory for more
information about obtaining a pseudo-tty.

strerror() and SunOS
--------------------

The standard way of getting the error message for an error value in
ANSI C is the function strerror().  SunOS does not define strerror().

An incorrect solution is to declare sys_nerr and sys_errlist and use
them directly.  Not only is this solution nonstandard, but modern
operating systems often have their own declarations of those
variables, which may conflict with your declarations.

For a program using imake, an appropriate way to detect the problem
is:

        #define HAVE_STRERROR
        #if defined(sun) && !defined(__svr4__)
        /* SunOS 4.1.3_U1 doesn't have strerror().  Use sys_errlist
         * instead. */
        #undef HAVE_STRERROR
        #endif

For a program using autoconf, put AC_CHECK_FUNC(strerror) in your
configure.in.

In either case, an appropriate workaround is:

        #ifndef HAVE_STRERROR
        extern const char *const sys_errlist[];
        #define strerror(x) (sys_errlist[x])
        #endif