incompatibility with glibc

Hello, there is a compatibility problem with the unix.a library and the
current glibc 2.1.3-6 in Debian unstable (sid). It concerns the error.h
and error.c files.  At least daemontools, djbdns, and qmail are
affected.

The problem occurs when a Debian/unstable machine is upgraded to the
recent glibc 2.1.3-6. The errno declaration/implementation in error.h
doesn't work properly anymore. This causes some binaries to fail to
start.  I think this isn't Debian specific, but introduced by upstream
of the GNU C Library.  The Debian glibc people usually take patches from
upstream to include into Debian. 

Here's an example with daemontools' supervise on Debian/unstable:

libc6_2.1.3-5 (and libc6_dev-2.1.3-5) is installed:

 # cd /package/admin/daemontools-0.76/compile
 # make clean it >/dev/null
 [some warnings]
 # rm rts-tmp/test.sv/down
 # ./supervise rts-tmp/test.sv
 second
 #

Ok, this works.

Upgrading to libc6_2.1.3-6:

 # dpkg -i libc6_2.3.1-6_i386.deb libc6-dev_2.3.1-6_i386.deb 
 (Reading database ... 63341 files and directories currently installed.)
 Preparing to replace libc6 2.3.1-6 (using libc6_2.3.1-6_i386.deb) ...
 [...]
 # ./supervise rts-tmp/test.sv
 supervise: fatal: unable to stat rts-tmp/test.sv/down: no error
 # echo $?
 111
 # make clean it >/dev/null
 pathexec_run.c: In function `pathexec_run':
 pathexec_run.c:18: warning: implicit declaration of function `execve'
 chkshsgr.c: In function `main':
 chkshsgr.c:10: warning: passing arg 2 of `getgroups' from incompatible pointer type
 chkshsgr.c:10: warning: implicit declaration of function `setgroups'
 prot.c: In function `prot_gid':
 prot.c:13: warning: implicit declaration of function `setgroups'
 prot.c:15: warning: implicit declaration of function `setgid'
 prot.c: In function `prot_uid':
 prot.c:20: warning: implicit declaration of function `setuid'
 seek_set.c: In function `seek_set':
 seek_set.c:9: warning: implicit declaration of function `lseek'
 envdir.o(.text+0x23f): In function `main':
 : undefined reference to `errno'
 envdir.o(.text+0x260): In function `main':
 : undefined reference to `errno'
 unix.a(openreadclose.o)(.text+0x22): In function `openreadclose':
 : undefined reference to `errno'
 unix.a(pathexec_run.o)(.text+0x10d): In function `pathexec_run':
 : undefined reference to `errno'
 unix.a(pathexec_run.o)(.text+0x14b): In function `pathexec_run':
 : undefined reference to `errno'
 unix.a(readclose.o)(.text+0x58): more undefined references to `errno' follow
 collect2: ld returned 1 exit status
 make: *** [envdir] Error 1
 #

As far as I've investigated this, the GNU C Library isn't doing anything
wrong.  Their info- and man-page for errno(3) states:

 SYNOPSIS
       #include <errno.h>
 [...]
       errno  is  defined  by  the ISO C standard to be a modifiable lvalue of
       type int, and must not be explicitly declared; errno may  be  a macro.
       errno  is  thread-local;  setting  it in one thread does not affect its
       value in any other thread.

But:
 # head /package/admin/daemontools-0.76/compile/error.h 
 /* Public domain. */
 
 #ifndef ERROR_H
 #define ERROR_H
 
 extern int errno;
 
 extern int error_intr;
 extern int error_nomem;
 extern int error_noent;
 #

Inserting '#include <errno.h>' after '#define ERROR_H' seems to solve
the problem: compiling and testing daemontools with libc6_2.1.2-6 works,
compiling and testing daemontools with libc6_2.1.2-5 works, and those
binaries compiled with libc6_2.1.2-5 still work after upgrading to
libc6_2.1.2-6.  I'm not sure about compatibility with other libc's
though.

I appreciate any input that helps solving this problem generally. If
desired I can provide more detailed information such as a diff between
libc6_2.1.2-5 and libc6_2.1.2-6 or debian- and upstream changelog.

Thanks, Gerrit.