include/shlib-compat.h

   1 /* Macros for managing ABI-compatibility definitions using ELF symbol versions.
   2    Copyright (C) 2000-2020 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #ifndef _SHLIB_COMPAT_H
  20 #define _SHLIB_COMPAT_H 1
  21
  22 # include <abi-versions.h>
  23
  24 #ifdef SHARED
  25
  26 /* The file abi-versions.h (generated by scripts/abi-versions.awk) defines
  27    symbols like `ABI_libm_GLIBC_2_0' for each version set in the source
  28    code for each library.  For a version set that is subsumed by a later
  29    version set, the definition gives the subsuming set, i.e. if GLIBC_2_0
  30    is subsumed by GLIBC_2_1, then ABI_libm_GLIBC_2_0 == ABI_libm_GLIBC_2_1.
  31    Each version set that is to be distinctly defined in the output has an
  32    unique positive integer value, increasing with newer versions.  Thus,
  33    evaluating two ABI_* symbols reduces to integer values that differ only
  34    when the two version sets named are in fact two different ABIs we are
  35    supporting.  If these do not differ, then there is no need to compile in
  36    extra code to support this version set where it has been superseded by a
  37    newer version.  The compatibility code should be conditionalized with
  38    e.g. `#if SHLIB_COMPAT (libm, GLIBC_2_0, GLIBC_2_2)' for code introduced
  39    in the GLIBC_2.0 version and obsoleted in the GLIBC_2.2 version.  */
  40
  41 # define SHLIB_COMPAT(lib, introduced, obsoleted)                             \
  42   _SHLIB_COMPAT (lib, introduced, obsoleted)
  43 # define _SHLIB_COMPAT(lib, introduced, obsoleted)                            \
  44   (IS_IN (lib)                                                                \
  45    && (!(ABI_##lib##_##obsoleted - 0)                                         \
  46        || ((ABI_##lib##_##introduced - 0) < (ABI_##lib##_##obsoleted - 0))))
  47
  48 /* That header also defines symbols like `VERSION_libm_GLIBC_2_1' to
  49    the version set name to use for e.g. symbols first introduced into
  50    libm in the GLIBC_2.1 version.  Definitions of symbols with explicit
  51    versions should look like:
  52         versioned_symbol (libm, new_foo, foo, GLIBC_2_1);
  53    This will define the symbol `foo' with the appropriate default version,
  54    i.e. either GLIBC_2.1 or the "earliest version" specified in
  55    shlib-versions if that is newer.  */
  56
  57 # define versioned_symbol(lib, local, symbol, version) \
  58   versioned_symbol_1 (lib, local, symbol, version)
  59 # define versioned_symbol_1(lib, local, symbol, version) \
  60   versioned_symbol_2 (local, symbol, VERSION_##lib##_##version)
  61 # define versioned_symbol_2(local, symbol, name) \
  62   default_symbol_version (local, symbol, name)
  63
  64 # define compat_symbol(lib, local, symbol, version) \
  65   compat_symbol_reference (lib, local, symbol, version)
  66
  67 /* This is similar to compat_symbol, but allows versioning the same symbol
  68    to multiple version without having multiple symbol definitions.  For
  69    instance:
  70
  71    #if (SHLIB_COMPAT (libpthread, GLIBC_2_1_2, GLIBC_2_2))
  72    compat_symbol_unique (libc, old_foo, GLIBC_2_1_2)
  73    #endif
  74
  75    #if (SHLIB_COMPAT (libpthread, GLIBC_2_2_6, GLIBC_2_3))
  76    compat_symbol_unique (libc, old_foo, GLIBC_2_2_6)
  77    #endif
  78
  79    Internally it creates a unique strong alias to the input symbol and
  80    creates one compat_symbol on the alias.  Using the above example,
  81    it is similar to:
  82
  83    #if (SHLIB_COMPAT (libpthread, GLIBC_2_1_2, GLIBC_2_2))
  84    strong_alias (old_foo, old_foo__COUNTER__)
  85    compat_symbol (libc, old_foo__COUNTER__, foo, GLIBC_2_2)
  86    #endif.
  87
  88    With __COUNTER__ being a monotonic number generated by the compiler.  */
  89
  90 # define __compat_symbol_unique_concat(x, y) x ## y
  91 # define _compat_symbol_unique_concat(x, y) \
  92   __compat_symbol_unique_concat (x, y)
  93 # define _compat_symbol_unique_alias(name) \
  94   _compat_symbol_unique_concat (name, __COUNTER__)
  95 # define _compat_symbol_unique(lib, orig_name, name, version) \
  96   strong_alias (orig_name, name) \
  97   compat_symbol (lib, name, orig_name, version)
  98 # define compat_symbol_unique(lib, name, version) \
  99   _compat_symbol_unique (lib, name, _compat_symbol_unique_alias (name), \
 100                          version)
 101
 102 #else
 103
 104 /* Not compiling ELF shared libraries at all, so never any old versions.  */
 105 # define SHLIB_COMPAT(lib, introduced, obsoleted)       0
 106
 107 /* No versions to worry about, just make this the global definition.  */
 108 # define versioned_symbol(lib, local, symbol, version) \
 109   weak_alias (local, symbol)
 110
 111 /* This should not appear outside `#if SHLIB_COMPAT (...)'.  */
 112 # define compat_symbol(lib, local, symbol, version) ...
 113 # define compat_symbol_unique(lib, name, version) ...
 114
 115 #endif
 116
 117 /* Use compat_symbol_reference for a reference *or* definition of a
 118    specific version of a symbol.  Definitions are primarily used to
 119    ensure tests reference the exact compat symbol required, or define an
 120    interposing symbol of the right version e.g. __malloc_initialize_hook
 121    in mcheck-init.c.  Use compat_symbol to define such a symbol within
 122    the shared libraries that are built for users.  */
 123 #define compat_symbol_reference(lib, local, symbol, version) \
 124   compat_symbol_reference_1 (lib, local, symbol, version)
 125 #define compat_symbol_reference_1(lib, local, symbol, version) \
 126   compat_symbol_reference_2 (local, symbol, VERSION_##lib##_##version)
 127 #define compat_symbol_reference_2(local, symbol, name) \
 128   symbol_version_reference (local, symbol, name)
 129
 130 # ifdef LINK_OBSOLETE_RPC
 131 /* Export the symbol for both static and dynamic linking.  */
 132 #  define libc_sunrpc_symbol(name, aliasname, version) \
 133   strong_alias (name, aliasname)
 134 # else
 135 /* Export the symbol only for shared-library compatibility.  */
 136 #  define libc_sunrpc_symbol(name, aliasname, version) \
 137   compat_symbol (libc, name, aliasname, version);
 138 # endif
 139
 140 /* The TEST_COMPAT macro acts just like the SHLIB_COMPAT macro except
 141    that it does not check IS_IN.  It is used by tests that are testing
 142    functionality that is only available in specific GLIBC versions.  */
 143
 144 # define TEST_COMPAT(lib, introduced, obsoleted)                              \
 145   _TEST_COMPAT (lib, introduced, obsoleted)
 146 # define _TEST_COMPAT(lib, introduced, obsoleted)                             \
 147    (!(ABI_##lib##_##obsoleted - 0)                                            \
 148        || ((ABI_##lib##_##introduced - 0) < (ABI_##lib##_##obsoleted - 0)))
 149
 150 #endif  /* shlib-compat.h */