include/shlib-compat.h

   1 /* Macros for managing ABI-compatibility definitions using ELF symbol versions.
   2    Copyright (C) 2000-2016 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    <http://www.gnu.org/licenses/>.  */
  18
  19 #ifndef _SHLIB_COMPAT_H
  20 #define _SHLIB_COMPAT_H 1
  21
  22 #ifdef SHARED
  23
  24 # include <abi-versions.h>
  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  36    extra code to support this version set where it has been superseded by a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_1 (lib, local, symbol, version)
  66 # define compat_symbol_1(lib, local, symbol, version) \
  67   compat_symbol_2 (local, symbol, VERSION_##lib##_##version)
  68 # define compat_symbol_2(local, symbol, name) \
  69   symbol_version (local, symbol, name)
  70
  71 #else
  72
  73 /* Not compiling ELF shared libraries at all, so never any old versions.  */
  74 # define SHLIB_COMPAT(lib, introduced, obsoleted)       0
  75
  76 /* No versions to worry about, just make this the global definition.  */
  77 # define versioned_symbol(lib, local, symbol, version) \
  78   weak_alias (local, symbol)
  79
  80 /* This should not appear outside `#if SHLIB_COMPAT (...)'.  */
  81 # define compat_symbol(lib, local, symbol, version) ...
  82
  83 #endif
  84
  85
  86 # ifdef LINK_OBSOLETE_RPC
  87 /* Export the symbol for both static and dynamic linking.  */
  88 #  define libc_sunrpc_symbol(name, aliasname, version) \
  89   strong_alias (name, aliasname)
  90 # else
  91 /* Export the symbol only for shared-library compatibility.  */
  92 #  define libc_sunrpc_symbol(name, aliasname, version) \
  93   compat_symbol (libc, name, aliasname, version);
  94 # endif
  95
  96 #endif  /* shlib-compat.h */