2 * Copyright 2017 Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
23 #include <folly/Portability.h>
24 #include <folly/Preprocessor.h>
27 * Check if the currently loaded version of a library is what you expect.
29 * It is possible for multiple versions of the same shared library to end up
30 * being loaded simultaneously in the same address space, usually with
33 * For example, let's say you have a shared library (foo) that doesn't keep
34 * binary compatbility between releases, and so each version is distributed as
35 * a SO with different SONAME. Let's say you build another shared library, bar
36 * that depends on version 1 of foo: libbar.so depends on libfoo1.so.
37 * Your main executable now (baz) depends on version 2 of foo, and also
38 * depends on bar: baz depends on libfoo2.so and libbar.so.
40 * At load time, baz loads libfoo2.so first, then libbar.so; libbar.so will
41 * load libfoo1.so, but, as this is normal dynamic loading (and not explicit
42 * dlopen calls with RTLD_DEEPBIND), any symbols from libfoo1.so that are
43 * also present in libfoo2.so will be satisfied from the (already loaded)
46 * But foo does not preserve binary compatibility between versions, so all
47 * hell breaks loose (the symbols from libfoo2.so are not necessarily direct
48 * replacements of the identically-named symbols in libfoo1.so).
50 * It is better to crash with a helpful error message instead, which is what
51 * this macro provides. FOLLY_VERSION_CHECK verifies at load time that
52 * the compiled-in version is the same as the currently loaded version.
54 * Usage: use this macro at namespace scope in a .cpp file (IMPORTANT: NOT
55 * in the unnamed namespace):
57 * FOLLY_VERSION_CHECK(mylib, "1")
59 * The first argument identifies your library; the second argument is a
60 * string literal containing the desired version string.
62 * In order to avoid changing the file for each version, the version string
63 * could be provided on the compiler command line with -D:
65 * FOLLY_VERSION_CHECK(mylib, MYLIB_VERSION)
67 * ... and then commpile your file with -DMYLIB_VERSION=\"1\"
71 // MSVC doesn't support constructor priorities. Just pray it works, I guess.
72 // We could implement a link-time mechanism for MSVC,
73 // via #pragma detect_mismatch but that would only handle
74 // static library linking.
75 # define FOLLY_VERSION_CHECK_PRIORITY(Ret, name) \
76 __pragma(section(".CRT$XCU",read)) \
77 static Ret __cdecl name(void); \
78 __declspec(allocate(".CRT$XCU")) \
79 Ret (__cdecl*name##_)(void) = name; \
82 #elif defined(__APPLE__)
83 // OS X doesn't support constructor priorities. Just pray it works, I guess.
84 # define FOLLY_VERSION_CHECK_PRIORITY(Ret, name) \
85 __attribute__((__constructor__)) Ret name()
88 # define FOLLY_VERSION_CHECK_PRIORITY(Ret, name) \
89 __attribute__((__constructor__(101))) Ret name()
92 // Note that this is carefully crafted: PRODUCT##Version must have external
93 // linkage (so it collides among versions), versionCheck must have internal
94 // linkage (so it does NOT collide between versions); if we're trying to have
95 // multiple versions loaded at the same time, they must each run their copy
96 // of versionCheck, but share the PRODUCT##Version variable.
97 #define FOLLY_VERSION_CHECK(PRODUCT, VERSION) \
98 const char* PRODUCT##Version = VERSION; \
100 FOLLY_VERSION_CHECK_PRIORITY(void, versionCheck) { \
101 if (strcmp(PRODUCT##Version, VERSION)) { \
103 "Invalid %s version: desired [%s], currently loaded [%s]\n", \
104 FB_STRINGIZE(PRODUCT), PRODUCT##Version, VERSION); \