Add framework for tunables

The tunables framework allows us to uniformly manage and expose global
variables inside glibc as switches to users.  tunables/README has
instructions for glibc developers to add new tunables.

Tunables support can be enabled by passing the --enable-tunables
configure flag to the configure script.  This patch only adds a
framework and does not pose any limitations on how tunable values are
read from the user.  It also adds environment variables used in malloc
behaviour tweaking to the tunables framework as a PoC of the
compatibility interface.

	* manual/install.texi: Add --enable-tunables option.
	* INSTALL: Regenerate.
	* README.tunables: New file.
	* Makeconfig (CPPFLAGS): Define TOP_NAMESPACE.
	(before-compile): Generate dl-tunable-list.h early.
	* config.h.in: Add HAVE_TUNABLES.
	* config.make.in: Add have-tunables.
	* configure.ac: Add --enable-tunables option.
	* configure: Regenerate.
	* csu/init-first.c (__libc_init_first): Move
	__libc_init_secure earlier...
	* csu/init-first.c (LIBC_START_MAIN):... to here.
	Include dl-tunables.h, libc-internal.h.
	(LIBC_START_MAIN) [!SHARED]: Initialize tunables for static
	binaries.
	* elf/Makefile (dl-routines): Add dl-tunables.
	* elf/Versions (ld): Add __tunable_set_val to GLIBC_PRIVATE
	namespace.
	* elf/dl-support (_dl_nondynamic_init): Unset MALLOC_CHECK_
	only when !HAVE_TUNABLES.
	* elf/rtld.c (process_envvars): Likewise.
	* elf/dl-sysdep.c [HAVE_TUNABLES]: Include dl-tunables.h
	(_dl_sysdep_start): Call __tunables_init.
	* elf/dl-tunable-types.h: New file.
	* elf/dl-tunables.c: New file.
	* elf/dl-tunables.h: New file.
	* elf/dl-tunables.list: New file.
	* malloc/tst-malloc-usable-static.c: New test case.
	* malloc/Makefile (tests-static): Add it.
	* malloc/arena.c [HAVE_TUNABLES]: Include dl-tunables.h.
	Define TUNABLE_NAMESPACE.
	(DL_TUNABLE_CALLBACK (set_mallopt_check)): New function.
	(DL_TUNABLE_CALLBACK_FNDECL): New macro.  Use it to define
	callback functions.
	(ptmalloc_init): Set tunable values.
	* scripts/gen-tunables.awk: New file.
	* sysdeps/mach/hurd/dl-sysdep.c: Include dl-tunables.h.
	(_dl_sysdep_start): Call __tunables_init.

ChangeLog

@@ -1,3 +1,44 @@
+2016-12-31  Siddhesh Poyarekar  <[email protected]>
+
+	* manual/install.texi: Add --enable-tunables option.
+	* INSTALL: Regenerate.
+	* README.tunables: New file.
+	* Makeconfig (CPPFLAGS): Define TOP_NAMESPACE.
+	(before-compile): Generate dl-tunable-list.h early.
+	* config.h.in: Add HAVE_TUNABLES.
+	* config.make.in: Add have-tunables.
+	* configure.ac: Add --enable-tunables option.
+	* configure: Regenerate.
+	* csu/init-first.c (__libc_init_first): Move
+	__libc_init_secure earlier...
+	* csu/init-first.c (LIBC_START_MAIN):... to here.
+	Include dl-tunables.h, libc-internal.h.
+	(LIBC_START_MAIN) [!SHARED]: Initialize tunables for static
+	binaries.
+	* elf/Makefile (dl-routines): Add dl-tunables.
+	* elf/Versions (ld): Add __tunable_set_val to GLIBC_PRIVATE
+	namespace.
+	* elf/dl-support (_dl_nondynamic_init): Unset MALLOC_CHECK_
+	only when !HAVE_TUNABLES.
+	* elf/rtld.c (process_envvars): Likewise.
+	* elf/dl-sysdep.c [HAVE_TUNABLES]: Include dl-tunables.h
+	(_dl_sysdep_start): Call __tunables_init.
+	* elf/dl-tunable-types.h: New file.
+	* elf/dl-tunables.c: New file.
+	* elf/dl-tunables.h: New file.
+	* elf/dl-tunables.list: New file.
+	* malloc/tst-malloc-usable-static.c: New test case.
+	* malloc/Makefile (tests-static): Add it.
+	* malloc/arena.c [HAVE_TUNABLES]: Include dl-tunables.h.
+	Define TUNABLE_NAMESPACE.
+	(DL_TUNABLE_CALLBACK (set_mallopt_check)): New function.
+	(DL_TUNABLE_CALLBACK_FNDECL): New macro.  Use it to define
+	callback functions.
+	(ptmalloc_init): Set tunable values.
+	* scripts/gen-tunables.awk: New file.
+	* sysdeps/mach/hurd/dl-sysdep.c: Include dl-tunables.h.
+	(_dl_sysdep_start): Call __tunables_init.
+
 2016-12-31  Florian Weimer  <[email protected]>
 
 	* resolv/resolv.h (RES_BLAST): Deprecate.

INSTALL

@@ -169,6 +169,11 @@ will be used, and CFLAGS sets optimization options for the compiler.
      By default for x86_64, the GNU C Library is built with the vector
      math library.  Use this option to disable the vector math library.
 
+'--enable-tunables'
+     Tunables support allows additional library parameters to be
+     customized at runtime.  This is an experimental feature and affects
+     startup time and is thus disabled by default.
+
 '--build=BUILD-SYSTEM'
 '--host=HOST-SYSTEM'
      These options are for cross-compiling.  If you specify both options

Makeconfig

@@ -934,6 +934,11 @@ CPPFLAGS = $(config-extra-cppflags) $(CPPUNDEFS) $(CPPFLAGS-config) \
 	   $(foreach lib,$(libof-$(basename $(@F))) \
 			 $(libof-$(<F)) $(libof-$(@F)),$(CPPFLAGS-$(lib))) \
 	   $(CPPFLAGS-$(<F)) $(CPPFLAGS-$(@F)) $(CPPFLAGS-$(basename $(@F)))
+
+ifeq (yes,$(have-tunables))
+CPPFLAGS += -DTOP_NAMESPACE=glibc
+endif
+
 override CFLAGS	= -std=gnu11 -fgnu89-inline $(config-extra-cflags) \
 		  $(filter-out %frame-pointer,$(+cflags)) $(+gccwarn-c) \
 		  $(sysdep-CFLAGS) $(CFLAGS-$(suffix $@)) $(CFLAGS-$(<F)) \
@@ -1108,6 +1113,17 @@ $(common-objpfx)libc-modules.stmp: $(..)scripts/gen-libc-modules.awk \
 
 endif
 
+# Build the tunables list header early since it could be used by any module in
+# glibc.
+ifeq (yes,$(have-tunables))
+before-compile += $(common-objpfx)dl-tunable-list.h
+
+$(common-objpfx)dl-tunable-list.h: $(..)scripts/gen-tunables.awk \
+				   $(..)elf/dl-tunables.list
+	$(AWK) -f $^ > [email protected]
+	mv [email protected] $@
+endif
+
 common-generated += libc-modules.h libc-modules.stmp
 
 # The name under which the run-time dynamic linker is installed.

README.tunables

@@ -0,0 +1,85 @@
+			TUNABLE FRAMEWORK
+			=================
+
+Tunables is a feature in the GNU C Library that allows application authors and
+distribution maintainers to alter the runtime library behaviour to match their
+workload.
+
+The tunable framework allows modules within glibc to register variables that
+may be tweaked through an environment variable.  It aims to enforce a strict
+namespace rule to bring consistency to naming of these tunable environment
+variables across the project.  This document is a guide for glibc developers to
+add tunables to the framework.
+
+ADDING A NEW TUNABLE
+--------------------
+
+The TOP_NAMESPACE macro is defined by default as 'glibc'.  If distributions
+intend to add their own tunables, they should do so in a different top
+namespace by overriding the TOP_NAMESPACE macro for that tunable.  Downstream
+implementations are discouraged from using the 'glibc' top namespace for
+tunables they don't already have consensus to push upstream.
+
+There are two steps to adding a tunable:
+
+1. Add a tunable ID:
+
+Modules that wish to use the tunables interface must define the
+TUNABLE_NAMESPACE macro.  Following this, for each tunable you want to
+add, make an entry in elf/dl-tunables.list.  The format of the file is as
+follows:
+
+TOP_NAMESPACE {
+  NAMESPACE1 {
+    TUNABLE1 {
+      # tunable attributes, one per line
+    }
+    # A tunable with default attributes, i.e. string variable.
+    TUNABLE2
+    TUNABLE3 {
+      # its attributes
+    }
+  }
+  NAMESPACE2 {
+    ...
+  }
+}
+
+The list of allowed attributes are:
+
+- type:			Data type.  Defaults to STRING.  Allowed types are:
+			INT_32, SIZE_T and STRING.
+
+- minval:		Optional minimum acceptable value.  For a string type
+			this is the minimum length of the value.
+
+- maxval:		Optional maximum acceptable value.  For a string type
+			this is the maximum length of the value.
+
+- env_alias:		An alias environment variable
+
+- is_secure:		Specify whether the tunable should be read for setuid
+			binaries.  True allows the tunable to be read for
+			setuid binaries while false disables it.  Note that
+			even if this is set as true and the value is read, it
+			may not be used if it does not validate against the
+			acceptable values or is not considered safe by the
+			module.
+
+2. Call either the TUNABLE_SET_VALUE and pass into it the tunable name and a
+   pointer to the variable that should be set with the tunable value.
+   If additional work needs to be done after setting the value, use the
+   TUNABLE_SET_VALUE_WITH_CALLBACK instead and additionally pass a pointer to
+   the function that should be called if the tunable value has been set.
+
+FUTURE WORK
+-----------
+
+The framework currently only allows a one-time initialization of variables
+through environment variables and in some cases, modification of variables via
+an API call.  A future goals for this project include:
+
+- Setting system-wide and user-wide defaults for tunables through some
+  mechanism like a configuration file.
+
+- Allow tweaking of some tunables at runtime

config.h.in

@@ -256,4 +256,7 @@
 /* PowerPC32 uses fctidz for floating point to long long conversions.  */
 #define HAVE_PPC_FCTIDZ 0
 
+/* Build glibc with tunables support.  */
+#define HAVE_TUNABLES 0
+
 #endif

config.make.in

@@ -96,6 +96,7 @@ use-nscd = @use_nscd@
 build-hardcoded-path-in-tests= @hardcoded_path_in_tests@
 build-pt-chown = @build_pt_chown@
 enable-lock-elision = @enable_lock_elision@
+have-tunables = @have_tunables@
 
 # Build tools.
 CC = @CC@

configure

@@ -666,6 +666,7 @@ libc_cv_ssp
 base_machine
 add_on_subdirs
 add_ons
+have_tunables
 build_pt_chown
 build_nscd
 link_obsolete_rpc
@@ -782,6 +783,7 @@ enable_systemtap
 enable_build_nscd
 enable_nscd
 enable_pt_chown
+enable_tunables
 enable_mathvec
 with_cpu
 '
@@ -1452,6 +1454,7 @@ Optional Features:
   --disable-build-nscd    disable building and installing the nscd daemon
   --disable-nscd          library functions will not contact the nscd daemon
   --enable-pt_chown       Enable building and installing pt_chown
+  --enable-tunables       Enable tunables support
   --enable-mathvec        Enable building and installing mathvec [default
                           depends on architecture]
 
@@ -3698,6 +3701,19 @@ if test "$build_pt_chown" = yes; then
 
 fi
 
+# Check whether --enable-tunables was given.
+if test "${enable_tunables+set}" = set; then :
+  enableval=$enable_tunables; have_tunables=$enableval
+else
+  have_tunables=no
+fi
+
+
+if test "$have_tunables" = yes; then
+  $as_echo "#define HAVE_TUNABLES 1" >>confdefs.h
+
+fi
+
 # The abi-tags file uses a fairly simplistic model for name recognition that
 # can't distinguish i486-pc-linux-gnu fully from i486-pc-gnu.  So we mutate a
 # $host_os of `gnu*' here to be `gnu-gnu*' just so that it can tell.

configure.ac

@@ -421,6 +421,16 @@ if test "$build_pt_chown" = yes; then
   AC_DEFINE(HAVE_PT_CHOWN)
 fi
 
+AC_ARG_ENABLE([tunables],
+	      [AS_HELP_STRING([--enable-tunables],
+	       [Enable tunables support])],
+	      [have_tunables=$enableval],
+	      [have_tunables=no])
+AC_SUBST(have_tunables)
+if test "$have_tunables" = yes; then
+  AC_DEFINE(HAVE_TUNABLES)
+fi
+
 # The abi-tags file uses a fairly simplistic model for name recognition that
 # can't distinguish i486-pc-linux-gnu fully from i486-pc-gnu.  So we mutate a
 # $host_os of `gnu*' here to be `gnu-gnu*' just so that it can tell.

csu/init-first.c

@@ -72,8 +72,6 @@ _init (int argc, char **argv, char **envp)
   __environ = envp;
 
 #ifndef SHARED
-  __libc_init_secure ();
-
   /* First the initialization which normally would be done by the
      dynamic linker.  */
   _dl_non_dynamic_init ();

csu/libc-start.c

@@ -21,6 +21,9 @@
 #include <unistd.h>
 #include <ldsodefs.h>
 #include <exit-thread.h>
+#include <libc-internal.h>
+
+#include <elf/dl-tunables.h>
 
 extern void __libc_init_first (int argc, char **argv, char **envp);
 
@@ -174,6 +177,11 @@ LIBC_START_MAIN (int (*main) (int, char **, char ** MAIN_AUXVEC_DECL),
         }
     }
 
+  /* Initialize very early so that tunables can use it.  */
+  __libc_init_secure ();
+
+  __tunables_init (__environ);
+
   /* Perform IREL{,A} relocations.  */
   apply_irel ();
 

elf/Makefile

@@ -35,6 +35,11 @@ dl-routines	= $(addprefix dl-,load lookup object reloc deps hwcaps \
 ifeq (yes,$(use-ldconfig))
 dl-routines += dl-cache
 endif
+
+ifeq (yes,$(have-tunables))
+dl-routines += dl-tunables
+endif
+
 all-dl-routines = $(dl-routines) $(sysdep-dl-routines)
 # But they are absent from the shared libc, because that code is in ld.so.
 elide-routines.os = $(all-dl-routines) dl-support enbl-secure dl-origin \

elf/Versions

@@ -70,5 +70,8 @@ ld {
 
     # Internal error handling support.  Interposed by libc.so.
     _dl_signal_error; _dl_catch_error;
+
+    # Set value of a tunable.
+    __tunable_set_val;
   }
 }

elf/dl-support.c

@@ -354,8 +354,10 @@ _dl_non_dynamic_init (void)
 	  cp = (const char *) __rawmemchr (cp, '\0') + 1;
 	}
 
+#if !HAVE_TUNABLES
       if (__access ("/etc/suid-debug", F_OK) != 0)
 	__unsetenv ("MALLOC_CHECK_");
+#endif
     }
 
 #ifdef DL_PLATFORM_INIT

elf/dl-sysdep.c

@@ -44,6 +44,8 @@
 #include <hp-timing.h>
 #include <tls.h>
 
+#include <dl-tunables.h>
+
 extern char **_environ attribute_hidden;
 extern char _end[] attribute_hidden;
 
@@ -219,6 +221,8 @@ _dl_sysdep_start (void **start_argptr,
     }
 #endif
 
+  __tunables_init (_environ);
+
 #ifdef DL_SYSDEP_INIT
   DL_SYSDEP_INIT;
 #endif

elf/dl-tunable-types.h

@@ -0,0 +1,46 @@
+/* Tunable type information.
+
+   Copyright (C) 2016 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/>.  */
+
+#ifndef _TUNABLE_TYPES_H_
+# define _TUNABLE_TYPES_H_
+#include <stddef.h>
+
+typedef void (*tunable_callback_t) (void *);
+
+typedef enum
+{
+  TUNABLE_TYPE_INT_32,
+  TUNABLE_TYPE_SIZE_T,
+  TUNABLE_TYPE_STRING
+} tunable_type_code_t;
+
+typedef struct
+{
+  tunable_type_code_t type_code;
+  int64_t min;
+  int64_t max;
+} tunable_type_t;
+
+typedef union
+{
+  int64_t numval;
+  const char *strval;
+} tunable_val_t;
+
+#endif