ld.so: Add --list-tunables to print tunable values

Pass --list-tunables to ld.so to print tunables with min and max values.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

NEWS

@@ -9,6 +9,10 @@ Version 2.33
 
 Major new features:
 
+* The dynamic linker accepts the --list-tunables argument which prints
+  all the supported tunables.  This option is disable if glibc is
+  configured with tunables disabled (--enable-tunables=no).
+
 * The dynamic linker accepts the --argv0 argument and provides opportunity
   to change argv[0] string.
 

elf/Makefile

@@ -45,6 +45,10 @@ dl-routines += dl-tunables
 tunables-type = $(addprefix TUNABLES_FRONTEND_,$(have-tunables))
 CPPFLAGS-dl-tunables.c += -DTUNABLES_FRONTEND=$(tunables-type)
 
+ifeq (yesyes,$(build-shared)$(run-built-tests))
+tests-special += $(objpfx)list-tunables.out
+endif
+
 # Make sure that the compiler does not insert any library calls in tunables
 # code paths.
 ifeq (yes,$(have-loop-to-function))
@@ -1896,3 +1900,10 @@ $(objpfx)tst-glibc-hwcaps-mask.out: \
 # Generic dependency for sysdeps implementation of
 # tst-glibc-hwcaps-cache.
 $(objpfx)tst-glibc-hwcaps-cache.out: $(objpfx)tst-glibc-hwcaps
+
+$(objpfx)list-tunables.out: tst-rtld-list-tunables.sh $(objpfx)ld.so
+	$(SHELL) $< $(objpfx)ld.so '$(test-wrapper-env)' \
+	    '$(run_program_env)' > $(objpfx)/tst-rtld-list-tunables.out
+	cmp tst-rtld-list-tunables.exp \
+	    $(objpfx)/tst-rtld-list-tunables.out > $@; \
+	$(evaluate-test)

elf/dl-main.h

@@ -63,7 +63,7 @@ struct audit_list
 enum rtld_mode
   {
     rtld_mode_normal, rtld_mode_list, rtld_mode_verify, rtld_mode_trace,
-    rtld_mode_help,
+    rtld_mode_list_tunables, rtld_mode_help,
   };
 
 /* Aggregated state information extracted from environment variables

elf/dl-tunables.c

@@ -26,6 +26,7 @@
 #include <sysdep.h>
 #include <fcntl.h>
 #include <ldsodefs.h>
+#include <array_length.h>
 
 #define TUNABLES_INTERNAL 1
 #include "dl-tunables.h"
@@ -398,6 +399,48 @@ __tunables_init (char **envp)
     }
 }
 
+void
+__tunables_print (void)
+{
+  for (int i = 0; i < array_length (tunable_list); i++)
+    {
+      const tunable_t *cur = &tunable_list[i];
+      if (cur->type.type_code == TUNABLE_TYPE_STRING
+	  && cur->val.strval == NULL)
+	_dl_printf ("%s:\n", cur->name);
+      else
+	{
+	  _dl_printf ("%s: ", cur->name);
+	  switch (cur->type.type_code)
+	    {
+	    case TUNABLE_TYPE_INT_32:
+	      _dl_printf ("%d (min: %d, max: %d)\n",
+			  (int) cur->val.numval,
+			  (int) cur->type.min,
+			  (int) cur->type.max);
+	      break;
+	    case TUNABLE_TYPE_UINT_64:
+	      _dl_printf ("0x%lx (min: 0x%lx, max: 0x%lx)\n",
+			  (long int) cur->val.numval,
+			  (long int) cur->type.min,
+			  (long int) cur->type.max);
+	      break;
+	    case TUNABLE_TYPE_SIZE_T:
+	      _dl_printf ("0x%Zx (min: 0x%Zx, max: 0x%Zx)\n",
+			  (size_t) cur->val.numval,
+			  (size_t) cur->type.min,
+			  (size_t) cur->type.max);
+	      break;
+	    case TUNABLE_TYPE_STRING:
+	      _dl_printf ("%s\n", cur->val.strval);
+	      break;
+	    default:
+	      __builtin_unreachable ();
+	    }
+	}
+    }
+}
+
 /* Set the tunable value.  This is called by the module that the tunable exists
    in. */
 void

elf/dl-tunables.h

@@ -69,9 +69,11 @@ typedef struct _tunable tunable_t;
 # include "dl-tunable-list.h"
 
 extern void __tunables_init (char **);
+extern void __tunables_print (void);
 extern void __tunable_get_val (tunable_id_t, void *, tunable_callback_t);
 extern void __tunable_set_val (tunable_id_t, void *, void *, void *);
 rtld_hidden_proto (__tunables_init)
+rtld_hidden_proto (__tunables_print)
 rtld_hidden_proto (__tunable_get_val)
 rtld_hidden_proto (__tunable_set_val)
 

elf/dl-usage.c

@@ -255,7 +255,12 @@ setting environment variables (which would be inherited by subprocesses).\n\
                         in LIST\n\
   --audit LIST          use objects named in LIST as auditors\n\
   --preload LIST        preload objects named in LIST\n\
-  --argv0 STRING        set argv[0] to STRING before running\n\
+  --argv0 STRING        set argv[0] to STRING before running\n"
+#if HAVE_TUNABLES
+"\
+  --list-tunables       list all tunables with minimum and maximum values\n"
+#endif
+"\
   --help                display this help and exit\n\
   --version             output version information and exit\n\
 \n\

elf/rtld.c

@@ -50,6 +50,7 @@
 #include <dl-main.h>
 #include <list.h>
 #include <gnu/lib-names.h>
+#include <dl-tunables.h>
 
 #include <assert.h>
 
@@ -1276,6 +1277,16 @@ dl_main (const ElfW(Phdr) *phdr,
 	    _dl_argc -= 2;
 	    _dl_argv += 2;
 	  }
+#if HAVE_TUNABLES
+	else if (! strcmp (_dl_argv[1], "--list-tunables"))
+	  {
+	    state.mode = rtld_mode_list_tunables;
+
+	    ++_dl_skip_args;
+	    --_dl_argc;
+	    ++_dl_argv;
+	  }
+#endif
 	else if (strcmp (_dl_argv[1], "--help") == 0)
 	  {
 	    state.mode = rtld_mode_help;
@@ -1296,6 +1307,14 @@ dl_main (const ElfW(Phdr) *phdr,
 	else
 	  break;
 
+#if HAVE_TUNABLES
+      if (__glibc_unlikely (state.mode == rtld_mode_list_tunables))
+	{
+	  __tunables_print ();
+	  _exit (0);
+	}
+#endif
+
       /* If we have no further argument the program was called incorrectly.
 	 Grant the user some education.  */
       if (_dl_argc < 2)

elf/tst-rtld-list-tunables.exp

@@ -0,0 +1,14 @@
+glibc.malloc.arena_max: 0x0 (min: 0x1, max: 0x[f]+)
+glibc.malloc.arena_test: 0x0 (min: 0x1, max: 0x[f]+)
+glibc.malloc.check: 0 (min: 0, max: 3)
+glibc.malloc.mmap_max: 0 (min: -2147483648, max: 2147483647)
+glibc.malloc.mmap_threshold: 0x0 (min: 0x0, max: 0x[f]+)
+glibc.malloc.mxfast: 0x0 (min: 0x0, max: 0x[f]+)
+glibc.malloc.perturb: 0 (min: 0, max: 255)
+glibc.malloc.tcache_count: 0x0 (min: 0x0, max: 0x[f]+)
+glibc.malloc.tcache_max: 0x0 (min: 0x0, max: 0x[f]+)
+glibc.malloc.tcache_unsorted_limit: 0x0 (min: 0x0, max: 0x[f]+)
+glibc.malloc.top_pad: 0x0 (min: 0x0, max: 0x[f]+)
+glibc.malloc.trim_threshold: 0x0 (min: 0x0, max: 0x[f]+)
+glibc.rtld.nns: 0x4 (min: 0x1, max: 0x10)
+glibc.rtld.optional_static_tls: 0x200 (min: 0x0, max: 0x[f]+)

elf/tst-rtld-list-tunables.sh

@@ -0,0 +1,34 @@
+#!/bin/sh
+# Test for --list-tunables option ld.so.
+# Copyright (C) 2021 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
+# <https://www.gnu.org/licenses/>.
+
+set -e
+
+rtld=$1
+test_wrapper_env=$2
+run_program_env=$3
+
+LC_ALL=C
+export LC_ALL
+
+${test_wrapper_env} \
+${run_program_env} \
+$rtld --list-tunables \
+| sort -u \
+| egrep "(rtld|malloc)" \
+| sed -e "s/0xf\+/0x[f]+/"

manual/tunables.texi

@@ -28,6 +28,44 @@ Finally, the set of tunables available may vary between distributions as
 the tunables feature allows distributions to add their own tunables under
 their own namespace.
 
+Passing @option{--list-tunables} to the dynamic loader to print all
+tunables with minimum and maximum values:
+
+@example
+$ /lib64/ld-linux-x86-64.so.2 --list-tunables
+glibc.rtld.nns: 0x4 (min: 0x1, max: 0x10)
+glibc.elision.skip_lock_after_retries: 3 (min: -2147483648, max: 2147483647)
+glibc.malloc.trim_threshold: 0x0 (min: 0x0, max: 0xffffffffffffffff)
+glibc.malloc.perturb: 0 (min: 0, max: 255)
+glibc.cpu.x86_shared_cache_size: 0x100000 (min: 0x0, max: 0xffffffffffffffff)
+glibc.mem.tagging: 0 (min: 0, max: 255)
+glibc.elision.tries: 3 (min: -2147483648, max: 2147483647)
+glibc.elision.enable: 0 (min: 0, max: 1)
+glibc.cpu.x86_rep_movsb_threshold: 0x1000 (min: 0x100, max: 0xffffffffffffffff)
+glibc.malloc.mxfast: 0x0 (min: 0x0, max: 0xffffffffffffffff)
+glibc.elision.skip_lock_busy: 3 (min: -2147483648, max: 2147483647)
+glibc.malloc.top_pad: 0x0 (min: 0x0, max: 0xffffffffffffffff)
+glibc.cpu.x86_rep_stosb_threshold: 0x800 (min: 0x1, max: 0xffffffffffffffff)
+glibc.cpu.x86_non_temporal_threshold: 0xc0000 (min: 0x0, max: 0xffffffffffffffff)
+glibc.cpu.x86_shstk:
+glibc.cpu.hwcap_mask: 0x6 (min: 0x0, max: 0xffffffffffffffff)
+glibc.malloc.mmap_max: 0 (min: -2147483648, max: 2147483647)
+glibc.elision.skip_trylock_internal_abort: 3 (min: -2147483648, max: 2147483647)
+glibc.malloc.tcache_unsorted_limit: 0x0 (min: 0x0, max: 0xffffffffffffffff)
+glibc.cpu.x86_ibt:
+glibc.cpu.hwcaps:
+glibc.elision.skip_lock_internal_abort: 3 (min: -2147483648, max: 2147483647)
+glibc.malloc.arena_max: 0x0 (min: 0x1, max: 0xffffffffffffffff)
+glibc.malloc.mmap_threshold: 0x0 (min: 0x0, max: 0xffffffffffffffff)
+glibc.cpu.x86_data_cache_size: 0x8000 (min: 0x0, max: 0xffffffffffffffff)
+glibc.malloc.tcache_count: 0x0 (min: 0x0, max: 0xffffffffffffffff)
+glibc.malloc.arena_test: 0x0 (min: 0x1, max: 0xffffffffffffffff)
+glibc.pthread.mutex_spin_count: 100 (min: 0, max: 32767)
+glibc.rtld.optional_static_tls: 0x200 (min: 0x0, max: 0xffffffffffffffff)
+glibc.malloc.tcache_max: 0x0 (min: 0x0, max: 0xffffffffffffffff)
+glibc.malloc.check: 0 (min: 0, max: 3)
+@end example
+
 @menu
 * Tunable names::  The structure of a tunable name
 * Memory Allocation Tunables::  Tunables in the memory allocation subsystem