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Make obsolete syscall wrappers into compat symbols (bug 18472)


Various Linux kernel syscalls have become obsolete over time.
Specifically, the following are obsolete in all kernel versions
supported by glibc, are not present for architectures more recently
added to the kernel, and as such, the wrapper functions for them
should be compat symbols, not in static libc and not available for new
links with shared libc.

* bdflush: in Linux 2.6, does nothing if present.

* create_module get_kernel_syms query_module: Linux 2.4 module
  interface, syscalls not present in Linux 2.6.

* uselib: part of the mechanism for loading a.out shared libraries,
  irrelevant with ELF.

This patch adds support for syscalls.list to list syscall aliases of
the form NAME@VERSION:OBSOLETED, with SHLIB_COMPAT conditionals being
generated for such aliases.  Those five syscalls are then made into
compat symbols (obsoleted in glibc 2.23, so future ports won't have
these symbols at all), with the header <sys/kdaemon.h> declaring
bdflush being removed.  When we move to 3.2 as minimum kernel version,
the same can be done for nfsservctl (removed in Linux 3.1) as well.

Tested for x86_64 and x86 (testsuite, as well as checking that the
symbols in question indeed become compat symbols, that they are indeed
omitted from static libc, and that the generated SHLIB_COMPAT
conditionals look right).

2015-12-04  Joseph Myers  <joseph@codesourcery.com>

	[BZ #18472]
	* sysdeps/unix/Makefile ($(objpfx)stub-syscalls.c): Handle entries
	for the form NAME@VERSION:OBSOLETED and generate SHLIB_COMPAT
	conditionals for them.
	* sysdeps/unix/make-syscalls.sh (emit_weak_aliases): Likewise.
	* sysdeps/unix/sysv/linux/sys/kdaemon.h: Remove file.
	* sysdeps/unix/sysv/linux/Makefile (sysdep_headers): Remove
	sys/kdaemon.h.
	* sysdeps/unix/sysv/linux/syscalls.list (bdflush): Make into
	compat-only syscall, obsoleted in glibc 2.23.
	(create_module): Likewise.
	(get_kernel_syms): Likewise.
	(query_module): Likewise.
	(uselib): Likewise.
	* manual/sysinfo.texi (System Parameters): Do not mention bdflush.

diff --git a/NEWS b/NEWS
index 37189f7..c15014c 100644
--- a/NEWS
+++ b/NEWS
@@ -47,6 +47,13 @@ Version 2.23
 * The obsolete header <regexp.h> has been removed.  Programs that require
   this header must be updated to use <regex.h> instead.
 
+* The obsolete functions bdflush, create_module, get_kernel_syms,
+  query_module and uselib are no longer available to newly linked binaries;
+  the header <sys/kdaemon.h> has been removed.  These functions and header
+  were specific to systems using the Linux kernel and could not usefully be
+  used with the GNU C Library on systems with version 2.6 or later of the
+  Linux kernel.
+
 * Optimized string, wcsmbs and memory functions for IBM z13.
   Implemented by Stefan Liebler.
 
diff --git a/manual/sysinfo.texi b/manual/sysinfo.texi
index e6c44d6..1fbfb95 100644
--- a/manual/sysinfo.texi
+++ b/manual/sysinfo.texi
@@ -1286,6 +1286,4 @@ parameters are:
 @code{gethostname}, @code{sethostname} (@xref{Host Identification}.)
 @item
 @code{uname} (@xref{Platform Type}.)
-@item
-@code{bdflush}
 @end itemize
diff --git a/sysdeps/unix/Makefile b/sysdeps/unix/Makefile
index 1770d1d..9faa669 100644
--- a/sysdeps/unix/Makefile
+++ b/sysdeps/unix/Makefile
@@ -59,8 +59,20 @@ $(objpfx)stub-syscalls.c: $(common-objpfx)sysd-syscalls \
 	   *@*) \
 	     ver=$${call##*@}; call=$${call%%@*}; \
 	     ver=`echo "$$ver" | sed 's/\./_/g'`; \
+	     case $$ver in \
+	     *:*) \
+	       compat_ver=$${ver#*:}; \
+	       ver=$${ver%%:*}; \
+	       compat_cond="SHLIB_COMPAT (libc, $$ver, $$compat_ver)"; \
+	       ;; \
+	     *) \
+	       compat_cond=""; \
+	       ;; \
+	     esac; \
+	     if [ "$$compat_cond" ]; then echo "#if $$compat_cond"; fi; \
 	     echo "strong_alias (_no_syscall, __$${call}_$${ver})"; \
-	     echo "compat_symbol (libc, __$${call}_$${ver}, $$call, $$ver);" \
+	     echo "compat_symbol (libc, __$${call}_$${ver}, $$call, $$ver);"; \
+	     if [ "$$compat_cond" ]; then echo "#endif"; fi; \
 	     ;; \
 	   *) echo "weak_alias (_no_syscall, $$call)"; \
 	      echo "stub_warning ($$call)"; \
diff --git a/sysdeps/unix/make-syscalls.sh b/sysdeps/unix/make-syscalls.sh
index fbf9660..bbef3eb3 100644
--- a/sysdeps/unix/make-syscalls.sh
+++ b/sysdeps/unix/make-syscalls.sh
@@ -81,12 +81,9 @@ emit_weak_aliases()
 
   # We use the <shlib-compat.h> macros to generate the versioned aliases
   # so that the version sets can be mapped to the configuration's
-  # minimum version set as per shlib-versions DEFAULT lines.  But note
-  # we don't generate any "#if SHLIB_COMPAT (...)" conditionals.  To do
-  # that we'd need to change the syscalls.list format so that it can
-  # list the "obsoleted" version set too.  If it ever arises that we
-  # have a syscall entry point that is obsoleted by a newer version set,
-  # we'll have to revamp all this.
+  # minimum version set as per shlib-versions DEFAULT lines.  If an
+  # entry point is specified in the form NAME@VERSION:OBSOLETED, a
+  # SHLIB_COMPAT conditional is generated.
   if [ $any_versioned = t ]; then
     echo "	 echo '#include <shlib-compat.h>'; \\"
   fi
@@ -113,7 +110,17 @@ emit_weak_aliases()
       *@*)
 	base=`echo $name | sed 's/@.*//'`
 	ver=`echo $name | sed 's/.*@//;s/\./_/g'`
-	echo "	 echo '#if defined SHARED && IS_IN (libc)'; \\"
+	case $ver in
+	  *:*)
+	    compat_ver=${ver#*:}
+	    ver=${ver%%:*}
+	    compat_cond=" && SHLIB_COMPAT (libc, $ver, $compat_ver)"
+	    ;;
+	  *)
+	    compat_cond=
+	    ;;
+	esac
+	echo "	 echo '#if defined SHARED && IS_IN (libc)$compat_cond'; \\"
 	if test -z "$vcount" ; then
 	  source=$strong
 	  vcount=1
diff --git a/sysdeps/unix/sysv/linux/Makefile b/sysdeps/unix/sysv/linux/Makefile
index 3eb4a7d..f6269ea 100644
--- a/sysdeps/unix/sysv/linux/Makefile
+++ b/sysdeps/unix/sysv/linux/Makefile
@@ -29,7 +29,7 @@ CFLAGS-tst-writev.c += "-DARTIFICIAL_LIMIT=0x80000000-__getpagesize()"
 # here and in any non-Linux configuration that uses it; other
 # configurations will not install the file.
 sysdep_headers += sys/mount.h sys/acct.h sys/sysctl.h \
-		  sys/klog.h sys/kdaemon.h \
+		  sys/klog.h \
 		  sys/user.h sys/prctl.h \
 		  sys/kd.h sys/soundcard.h sys/vt.h \
 		  sys/quota.h sys/fsuid.h \
diff --git a/sysdeps/unix/sysv/linux/sys/kdaemon.h b/sysdeps/unix/sysv/linux/sys/kdaemon.h
deleted file mode 100644
index 67ab6d3..0000000
--- a/sysdeps/unix/sysv/linux/sys/kdaemon.h
+++ /dev/null
@@ -1,32 +0,0 @@
-/* Copyright (C) 1996-2015 Free Software Foundation, Inc.
-   This file is part of the GNU C Library.
-
-   The GNU C Library is free software; you can redistribute it and/or
-   modify it under the terms of the GNU Lesser General Public
-   License as published by the Free Software Foundation; either
-   version 2.1 of the License, or (at your option) any later version.
-
-   The GNU C Library is distributed in the hope that it will be useful,
-   but WITHOUT ANY WARRANTY; without even the implied warranty of
-   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
-   Lesser General Public License for more details.
-
-   You should have received a copy of the GNU Lesser General Public
-   License along with the GNU C Library; if not, see
-   <http://www.gnu.org/licenses/>.  */
-
-/* Interfaces to control the various kernel daemons.  */
-
-#ifndef _SYS_KDAEMON_H
-
-#define _SYS_KDAEMON_H	1
-#include <features.h>
-
-__BEGIN_DECLS
-
-/* Start, flush, or tune the kernel's buffer flushing daemon.  */
-extern int bdflush (int __func, long int __data) __THROW;
-
-__END_DECLS
-
-#endif /* _SYS_KDAEMON_H */
diff --git a/sysdeps/unix/sysv/linux/syscalls.list b/sysdeps/unix/sysv/linux/syscalls.list
index 62bb3cc..caa6ccf 100644
--- a/sysdeps/unix/sysv/linux/syscalls.list
+++ b/sysdeps/unix/sysv/linux/syscalls.list
@@ -2,12 +2,12 @@
 
 adjtimex	adjtime	adjtimex	i:p	__adjtimex	adjtimex ntp_adjtime
 alarm		-	alarm		i:i	alarm
-bdflush		EXTRA	bdflush		i:ii	bdflush
+bdflush		EXTRA	bdflush		i:ii	__compat_bdflush	bdflush@GLIBC_2.0:GLIBC_2.23
 capget		EXTRA	capget		i:pp	capget
 capset		EXTRA	capset		i:pp	capset
 clock_adjtime	EXTRA	clock_adjtime	i:ip	clock_adjtime
 creat		-	creat		Ci:si	creat
-create_module	EXTRA	create_module	3	create_module
+create_module	EXTRA	create_module	3	__compat_create_module	create_module@GLIBC_2.0:GLIBC_2.23
 delete_module	EXTRA	delete_module	3	delete_module
 epoll_create	EXTRA	epoll_create	i:i	epoll_create
 epoll_create1	EXTRA	epoll_create1	i:i	epoll_create1
@@ -16,7 +16,7 @@ epoll_wait	EXTRA	epoll_wait	Ci:ipii	epoll_wait
 execve		-	execve		i:spp	__execve	execve
 fdatasync	-	fdatasync	Ci:i	fdatasync
 flock		-	flock		i:ii	__flock		flock
-get_kernel_syms	EXTRA	get_kernel_syms	i:p	get_kernel_syms
+get_kernel_syms	EXTRA	get_kernel_syms	i:p	__compat_get_kernel_syms	get_kernel_syms@GLIBC_2.0:GLIBC_2.23
 getegid		-	getegid		Ei:	__getegid	getegid
 geteuid		-	geteuid		Ei:	__geteuid	geteuid
 getpgid		-	getpgid		i:i	__getpgid	getpgid
@@ -53,7 +53,7 @@ pivot_root	EXTRA	pivot_root	i:ss	pivot_root
 poll		-	poll		Ci:pii	__libc_poll	__poll poll
 prctl		EXTRA	prctl		i:iiiii	__prctl		prctl
 putpmsg		-	putpmsg		i:ippii	putpmsg
-query_module	EXTRA	query_module	i:sipip	query_module
+query_module	EXTRA	query_module	i:sipip	__compat_query_module	query_module@GLIBC_2.0:GLIBC_2.23
 quotactl	EXTRA	quotactl	i:isip	quotactl
 remap_file_pages -	remap_file_pages i:piiii	__remap_file_pages remap_file_pages
 sched_getp	-	sched_getparam	i:ip	__sched_getparam	sched_getparam
@@ -78,7 +78,7 @@ swapon		-	swapon		i:si	__swapon	swapon
 swapoff		-	swapoff		i:s	__swapoff	swapoff
 tee		EXTRA	tee		Ci:iiii	tee
 unshare		EXTRA	unshare		i:i	unshare
-uselib		EXTRA	uselib		i:s	uselib
+uselib		EXTRA	uselib		i:s	__compat_uselib	uselib@GLIBC_2.0:GLIBC_2.23
 utime		-	utime		i:sP	utime
 vmsplice	EXTRA	vmsplice	Ci:iPii	vmsplice
 wait4		-	wait4		i:iWiP	__wait4		wait4

-- 
Joseph S. Myers
joseph@codesourcery.com


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