include/shlib-compat.h

   1 /* Macros for managing ABI-compatibility definitions using ELF symbol versions.
   2    Copyright (C) 2000-2021 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 /* The file abi-versions.h (generated by scripts/abi-versions.awk) defines
  25    symbols like `ABI_libm_GLIBC_2_0' for each version set in the source
  26    code for each library.  For a version set that is subsumed by a later
  27    version set, the definition gives the subsuming set, i.e. if GLIBC_2_0
  28    is subsumed by GLIBC_2_1, then ABI_libm_GLIBC_2_0 == ABI_libm_GLIBC_2_1.
  29    Each version set that is to be distinctly defined in the output has an
  30    unique positive integer value, increasing with newer versions.  Thus,
  31    evaluating two ABI_* symbols reduces to integer values that differ only
  32    when the two version sets named are in fact two different ABIs we are
  33    supporting.  If these do not differ, then there is no need to compile in
  34    extra code to support this version set where it has been superseded by a
  35    newer version.  */
  36 #define LIB_COMPAT(lib, introduced, obsoleted)                                \
  37   _LIB_COMPAT (lib, introduced, obsoleted)
  38 #define _LIB_COMPAT(lib, introduced, obsoleted)                               \
  39   (IS_IN (lib)                                                                \
  40    && (!(ABI_##lib##_##obsoleted - 0)                                         \
  41        || ((ABI_##lib##_##introduced - 0) < (ABI_##lib##_##obsoleted - 0))))
  42
  43 #ifdef SHARED
  44
  45 /* Similar to LIB_COMPAT, but evaluate to 0 for static build.  The
  46    compatibility code should be conditionalized with e.g.
  47    `#if SHLIB_COMPAT (libm, GLIBC_2_0, GLIBC_2_2)' for code introduced
  48    in the GLIBC_2.0 version and obsoleted in the GLIBC_2.2 version.  */
  49
  50 # define SHLIB_COMPAT(lib, introduced, obsoleted)                             \
  51   _LIB_COMPAT (lib, introduced, obsoleted)
  52
  53 /* That header also defines symbols like `VERSION_libm_GLIBC_2_1' to
  54    the version set name to use for e.g. symbols first introduced into
  55    libm in the GLIBC_2.1 version.  Definitions of symbols with explicit
  56    versions should look like:
  57         versioned_symbol (libm, new_foo, foo, GLIBC_2_1);
  58    This will define the symbol `foo' with the appropriate default version,
  59    i.e. either GLIBC_2.1 or the "earliest version" specified in
  60    shlib-versions if that is newer.  */
  61
  62 # define versioned_symbol(lib, local, symbol, version) \
  63   versioned_symbol_1 (lib, local, symbol, version)
  64 # define versioned_symbol_1(lib, local, symbol, version) \
  65   versioned_symbol_2 (local, symbol, VERSION_##lib##_##version)
  66 # define versioned_symbol_2(local, symbol, name) \
  67   default_symbol_version (local, symbol, name)
  68
  69 # define compat_symbol(lib, local, symbol, version) \
  70   compat_symbol_reference (lib, local, symbol, version)
  71
  72 /* This is similar to compat_symbol, but allows versioning the same symbol
  73    to multiple version without having multiple symbol definitions.  For
  74    instance:
  75
  76    #if (SHLIB_COMPAT (libpthread, GLIBC_2_1_2, GLIBC_2_2))
  77    compat_symbol_unique (libc, old_foo, GLIBC_2_1_2)
  78    #endif
  79
  80    #if (SHLIB_COMPAT (libpthread, GLIBC_2_2_6, GLIBC_2_3))
  81    compat_symbol_unique (libc, old_foo, GLIBC_2_2_6)
  82    #endif
  83
  84    Internally it creates a unique strong alias to the input symbol and
  85    creates one compat_symbol on the alias.  Using the above example,
  86    it is similar to:
  87
  88    #if (SHLIB_COMPAT (libpthread, GLIBC_2_1_2, GLIBC_2_2))
  89    strong_alias (old_foo, old_foo__COUNTER__)
  90    compat_symbol (libc, old_foo__COUNTER__, foo, GLIBC_2_2)
  91    #endif.
  92
  93    With __COUNTER__ being a monotonic number generated by the compiler.  */
  94
  95 # define __compat_symbol_unique_concat(x, y) x ## y
  96 # define _compat_symbol_unique_concat(x, y) \
  97   __compat_symbol_unique_concat (x, y)
  98 # define _compat_symbol_unique_alias(name) \
  99   _compat_symbol_unique_concat (name, __COUNTER__)
 100 # define _compat_symbol_unique(lib, orig_name, name, version) \
 101   strong_alias (orig_name, name) \
 102   compat_symbol (lib, name, orig_name, version)
 103 # define compat_symbol_unique(lib, name, version) \
 104   _compat_symbol_unique (lib, name, _compat_symbol_unique_alias (name), \
 105                          version)
 106
 107 #else
 108
 109 /* Not compiling ELF shared libraries at all, so never any old versions.  */
 110 # define SHLIB_COMPAT(lib, introduced, obsoleted)       0
 111
 112 /* No versions to worry about, just make this the global definition.  */
 113 # define versioned_symbol(lib, local, symbol, version) \
 114   weak_alias (local, symbol)
 115
 116 /* This should not appear outside `#if SHLIB_COMPAT (...)'.  */
 117 # define compat_symbol(lib, local, symbol, version) ...
 118 # define compat_symbol_unique(lib, name, version) ...
 119
 120 #endif
 121
 122 /* Use compat_symbol_reference for a reference *or* definition of a
 123    specific version of a symbol.  Definitions are primarily used to
 124    ensure tests reference the exact compat symbol required, or define an
 125    interposing symbol of the right version e.g. __malloc_initialize_hook
 126    in mcheck-init.c.  Use compat_symbol to define such a symbol within
 127    the shared libraries that are built for users.  */
 128 #define compat_symbol_reference(lib, local, symbol, version) \
 129   compat_symbol_reference_1 (lib, local, symbol, version)
 130 #define compat_symbol_reference_1(lib, local, symbol, version) \
 131   compat_symbol_reference_2 (local, symbol, VERSION_##lib##_##version)
 132 #define compat_symbol_reference_2(local, symbol, name) \
 133   symbol_version_reference (local, symbol, name)
 134
 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
 139 /* The TEST_COMPAT macro acts just like the SHLIB_COMPAT macro except
 140    that it does not check IS_IN.  It is used by tests that are testing
 141    functionality that is only available in specific GLIBC versions.  */
 142
 143 # define TEST_COMPAT(lib, introduced, obsoleted)                              \
 144   _TEST_COMPAT (lib, introduced, obsoleted)
 145 # define _TEST_COMPAT(lib, introduced, obsoleted)                             \
 146    (!(ABI_##lib##_##obsoleted - 0)                                            \
 147        || ((ABI_##lib##_##introduced - 0) < (ABI_##lib##_##obsoleted - 0)))
 148
 149 #endif  /* shlib-compat.h */