compatibility.rst revision 1.1.1.1 
1.. Copyright (C) 2015 Free Software Foundation, Inc.
2   Originally contributed by David Malcolm <dmalcolm@redhat.com>
3
4   This is free software: you can redistribute it and/or modify it
5   under the terms of the GNU General Public License as published by
6   the Free Software Foundation, either version 3 of the License, or
7   (at your option) any later version.
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9   This program is distributed in the hope that it will be useful, but
10   WITHOUT ANY WARRANTY; without even the implied warranty of
11   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
12   General Public License for more details.
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14   You should have received a copy of the GNU General Public License
15   along with this program.  If not, see
16   <http://www.gnu.org/licenses/>.
17
18.. default-domain:: c
19
20ABI and API compatibility
21=========================
22
23The libgccjit developers strive for ABI and API backward-compatibility:
24programs built against libgccjit.so stand a good chance of running
25without recompilation against newer versions of libgccjit.so, and
26ought to recompile without modification against newer versions of
27libgccjit.h.
28
29.. note:: The libgccjit++.h C++ API is more experimental, and less
30          locked-down at this time.
31
32API compatibility is achieved by extending the API rather than changing
33it.  For ABI compatiblity, we avoid bumping the SONAME, and instead use
34symbol versioning to tag each symbol, so that a binary linked against
35libgccjit.so is tagged according to the symbols that it uses.
36
37For example, :func:`gcc_jit_context_add_command_line_option` was added in
38``LIBGCCJIT_ABI_1``.  If a client program uses it, this can be detected
39from metadata by using ``objdump``:
40
41.. code-block:: bash
42
43   $ objdump -p testsuite/jit/test-extra-options.c.exe | tail -n 8
44
45   Version References:
46     required from libgccjit.so.0:
47       0x00824161 0x00 04 LIBGCCJIT_ABI_1
48       0x00824160 0x00 03 LIBGCCJIT_ABI_0
49     required from libc.so.6:
50
51You can see the symbol tags provided by libgccjit.so using ``objdump``:
52
53.. code-block:: bash
54
55   $ objdump -p libgccjit.so | less
56   [...snip...]
57   Version definitions:
58   1 0x01 0x0ff81f20 libgccjit.so.0
59   2 0x00 0x00824160 LIBGCCJIT_ABI_0
60   3 0x00 0x00824161 LIBGCCJIT_ABI_1
61           LIBGCCJIT_ABI_0
62   [...snip...]
63
64ABI symbol tags
65***************
66
67The initial release of libgccjit (in gcc 5.1) did not use symbol versioning.
68
69Newer releases use the following tags.
70
71.. _LIBGCCJIT_ABI_0:
72
73``LIBGCCJIT_ABI_0``
74-------------------
75
76All entrypoints in the initial release of libgccjit are tagged with
77``LIBGCCJIT_ABI_0``, to signify the transition to symbol versioning.
78
79Binaries built against older copies of ``libgccjit.so`` should
80continue to work, with this being handled transparently by the linker
81(see `this post
82<https://gcc.gnu.org/ml/gcc-patches/2015-06/msg02126.html>`_)
83
84.. _LIBGCCJIT_ABI_1:
85
86``LIBGCCJIT_ABI_1``
87-------------------
88``LIBGCCJIT_ABI_1`` covers the addition of
89:func:`gcc_jit_context_add_command_line_option`
90
91.. _LIBGCCJIT_ABI_2:
92
93``LIBGCCJIT_ABI_2``
94-------------------
95``LIBGCCJIT_ABI_2`` covers the addition of
96:func:`gcc_jit_context_set_bool_allow_unreachable_blocks`
97
98.. _LIBGCCJIT_ABI_3:
99
100``LIBGCCJIT_ABI_3``
101-------------------
102``LIBGCCJIT_ABI_3`` covers the addition of switch statements via API
103entrypoints:
104
105  * :func:`gcc_jit_block_end_with_switch`
106
107  * :func:`gcc_jit_case_as_object`
108
109  * :func:`gcc_jit_context_new_case`
110