elf/dl-tunables.h

   1 /* The tunable framework.  See the README to know how to use the tunable in
   2    a glibc module.
   3
   4    Copyright (C) 2016-2020 Free Software Foundation, Inc.
   5    This file is part of the GNU C Library.
   6
   7    The GNU C Library is free software; you can redistribute it and/or
   8    modify it under the terms of the GNU Lesser General Public
   9    License as published by the Free Software Foundation; either
  10    version 2.1 of the License, or (at your option) any later version.
  11
  12    The GNU C Library is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15    Lesser General Public License for more details.
  16
  17    You should have received a copy of the GNU Lesser General Public
  18    License along with the GNU C Library; if not, see
  19    <https://www.gnu.org/licenses/>.  */
  20
  21 #ifndef _TUNABLES_H_
  22 #define _TUNABLES_H_
  23
  24 #include <stdbool.h>
  25
  26 #if !HAVE_TUNABLES
  27 static inline void
  28 __always_inline
  29 __tunables_init (char **unused __attribute__ ((unused)))
  30 {
  31   /* This is optimized out if tunables are not enabled.  */
  32 }
  33 #else
  34
  35 # include <stddef.h>
  36 # include "dl-tunable-types.h"
  37
  38 /* A tunable.  */
  39 struct _tunable
  40 {
  41   const char *name;                     /* Internal name of the tunable.  */
  42   tunable_type_t type;                  /* Data type of the tunable.  */
  43   tunable_val_t val;                    /* The value.  */
  44   bool initialized;                     /* Flag to indicate that the tunable is
  45                                            initialized.  */
  46   tunable_seclevel_t security_level;    /* Specify the security level for the
  47                                            tunable with respect to AT_SECURE
  48                                            programs.  See description of
  49                                            tunable_seclevel_t to see a
  50                                            description of the values.
  51
  52                                            Note that even if the tunable is
  53                                            read, it may not get used by the
  54                                            target module if the value is
  55                                            considered unsafe.  */
  56   /* Compatibility elements.  */
  57   const char *env_alias;                /* The compatibility environment
  58                                            variable name.  */
  59 };
  60
  61 typedef struct _tunable tunable_t;
  62
  63 /* Full name for a tunable is top_ns.tunable_ns.id.  */
  64 # define TUNABLE_NAME_S(top,ns,id) #top "." #ns "." #id
  65
  66 # define TUNABLE_ENUM_NAME(__top,__ns,__id) TUNABLE_ENUM_NAME1 (__top,__ns,__id)
  67 # define TUNABLE_ENUM_NAME1(__top,__ns,__id) __top ## _ ## __ns ## _ ## __id
  68
  69 # include "dl-tunable-list.h"
  70
  71 extern void __tunables_init (char **);
  72 extern void __tunable_get_val (tunable_id_t, void *, tunable_callback_t);
  73 extern void __tunable_set_val (tunable_id_t, void *);
  74 rtld_hidden_proto (__tunables_init)
  75 rtld_hidden_proto (__tunable_get_val)
  76
  77 /* Define TUNABLE_GET and TUNABLE_SET in short form if TOP_NAMESPACE and
  78    TUNABLE_NAMESPACE are defined.  This is useful shorthand to get and set
  79    tunables within a module.  */
  80 #if defined TOP_NAMESPACE && defined TUNABLE_NAMESPACE
  81 # define TUNABLE_GET(__id, __type, __cb) \
  82   TUNABLE_GET_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, __type, __cb)
  83 # define TUNABLE_SET(__id, __type, __val) \
  84   TUNABLE_SET_FULL (TOP_NAMESPACE, TUNABLE_NAMESPACE, __id, __type, __val)
  85 #else
  86 # define TUNABLE_GET(__top, __ns, __id, __type, __cb) \
  87   TUNABLE_GET_FULL (__top, __ns, __id, __type, __cb)
  88 # define TUNABLE_SET(__top, __ns, __id, __type, __val) \
  89   TUNABLE_SET_FULL (__top, __ns, __id, __type, __val)
  90 #endif
  91
  92 /* Get and return a tunable value.  If the tunable was set externally and __CB
  93    is defined then call __CB before returning the value.  */
  94 # define TUNABLE_GET_FULL(__top, __ns, __id, __type, __cb) \
  95 ({                                                                            \
  96   tunable_id_t id = TUNABLE_ENUM_NAME (__top, __ns, __id);                    \
  97   __type ret;                                                                 \
  98   __tunable_get_val (id, &ret, __cb);                                         \
  99   ret;                                                                        \
 100 })
 101
 102 /* Set a tunable value.  */
 103 # define TUNABLE_SET_FULL(__top, __ns, __id, __type, __val) \
 104 ({                                                                            \
 105   __tunable_set_val (TUNABLE_ENUM_NAME (__top, __ns, __id),                   \
 106                         & (__type) {__val});                                  \
 107 })
 108
 109 /* Namespace sanity for callback functions.  Use this macro to keep the
 110    namespace of the modules clean.  */
 111 # define TUNABLE_CALLBACK(__name) _dl_tunable_ ## __name
 112
 113 # define TUNABLES_FRONTEND_valstring 1
 114 /* The default value for TUNABLES_FRONTEND.  */
 115 # define TUNABLES_FRONTEND_yes TUNABLES_FRONTEND_valstring
 116
 117 /* Compare two name strings, bounded by the name hardcoded in glibc.  */
 118 static __always_inline bool
 119 tunable_is_name (const char *orig, const char *envname)
 120 {
 121   for (;*orig != '\0' && *envname != '\0'; envname++, orig++)
 122     if (*orig != *envname)
 123       break;
 124
 125   /* The ENVNAME is immediately followed by a value.  */
 126   if (*orig == '\0' && *envname == '=')
 127     return true;
 128   else
 129     return false;
 130 }
 131
 132 #endif
 133 #endif