use of __gen_tempname

[Bruno Haible]

Hi Eric,

Sorry for the late remark. (I haven't been able to follow the tempname
thread.)

In lib/tempname.c you added code that uses the function __gen_tempname from
libc if it is present. I assume this is for glibc? This __gen_tempname
function is not part of the public ABI of glibc: it is not listed in any
of the 'Versions' files in glibc-2.3.6 nor glibc-2.5. In fact, on a
glibc-2.3.6 system where glibc was built with sufficiently recent gcc
and binutils, the symbol is not exported:

  $ nm /lib/libc.so.6 | grep gen_tempname
  000554b0 t __gen_tempname
  $ nm --dynamic /lib/libc.so.6 | grep gen_tempname
  $

This means that when a user builds binaries from this code on an older
glibc, the binaries refer to __gen_tempname and will refuse to run when
the user upgrades to glibc-2.3.6 or newer.

The same mistake has been made by the Sun engineers responsible for the
JDK 1.3.1 for Linux. They shipped hundreds of thousands of copies of a 'java'
binary referring to the symbol __libc_wait. Users then had a bad surprise
when they switched to a newer Linux distribution: their JDK stopped working.
Some of them asked me for advice, because they found my name in related
postings...

I think it is preferable to build a binary that is 1 KB bigger but
continues working after an OS upgrade. Hence this proposed patch.

2006-11-06  Bruno Haible  <address@hidden>

        * lib/tempname.c (gen_tempname): Remove variant that invokes
        __gen_tempname.
        * m4/tempname.m4 (gl_FUNC_GEN_TEMPNAME): Don't test for __gen_tempname.

*** gnulib-20061106/lib/tempname.c      2006-11-07 01:19:06.000000000 +0100
--- gnulib-20061106-modified/lib/tempname.c     2006-11-07 01:31:01.000000000 
+0100
***************
*** 200,206 ****
     __GT_DIR:          create a directory, which will be mode 0700.
  
     We use a clever algorithm to get hard-to-predict names. */
- #if _LIBC || !HAVE___GEN_TEMPNAME
  int
  __gen_tempname (char *tmpl, int kind)
  {
--- 200,205 ----
***************
*** 321,335 ****
    __set_errno (EEXIST);
    return -1;
  }
- 
- #else /* !_LIBC && HAVE___GEN_TEMPNAME */
- 
- # undef __gen_tempname
- extern int __gen_tempname (char *, int);
- int
- gen_tempname (char *tmpl, int kind)
- {
-   return __gen_tempname (tmpl, kind);
- }
- 
- #endif /* !_LIBC && HAVE___GEN_TEMPNAME */
--- 320,322 ----
*** gnulib-20061106/m4/tempname.m4      2006-10-27 15:51:23.000000000 +0200
--- gnulib-20061106-modified/m4/tempname.m4     2006-11-07 01:31:38.000000000 
+0100
***************
*** 1,16 ****
! #serial 1
  
  # Copyright (C) 2006 Free Software Foundation, Inc.
  # This file is free software; the Free Software Foundation
  # gives unlimited permission to copy and/or distribute it,
  # with or without modifications, as long as this notice is preserved.
  
- # glibc provides __gen_tempname as a wrapper for mk[ds]temp.  Expose
- # it as a public API, and provide it on systems that are lacking.
  AC_DEFUN([gl_FUNC_GEN_TEMPNAME],
  [
    AC_REQUIRE([AC_SYS_LARGEFILE])
-   AC_CHECK_FUNCS_ONCE([__gen_tempname])
  
    AC_LIBOBJ([tempname])
    gl_PREREQ_TEMPNAME
--- 1,13 ----
! #serial 2
  
  # Copyright (C) 2006 Free Software Foundation, Inc.
  # This file is free software; the Free Software Foundation
  # gives unlimited permission to copy and/or distribute it,
  # with or without modifications, as long as this notice is preserved.
  
  AC_DEFUN([gl_FUNC_GEN_TEMPNAME],
  [
    AC_REQUIRE([AC_SYS_LARGEFILE])
  
    AC_LIBOBJ([tempname])
    gl_PREREQ_TEMPNAME