Hiding instantiated templates in shared library created with g++
I have a file that contains the following:
#include When comp
-
In C++, if a template argument has limited visibility, this restriction is implicitly propagated to the template instantiation.
#include <map> class __attribute__((visibility ("hidden"))) A {}; void doSomething() { std::map<int, A> m; }should do the job.
-- edit --
One more thing, `#pragma GCC visibility' affects only namespace-scope declarations. Class members and template specializations are not affected (Visibility pragmas)讨论(0) -
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36022:
The std::namespace is supposed to be exposed and is marked as such in the libstdc++ headers.As for
#undef _GLIBCXX_VISIBILITY_ATTRhere is another quote:
If you were to hack in support for allowing namespace std to have hidden visibility, and run the testsuite with -fvisibility=hidden (see attached patch) you would notice the breakdown in testresults, with mass failures.讨论(0) -
Maybe you could use objcopy with the --strip-symbol option?
The option is described in the objcopy man page
This might get tedious though...
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Disclaimer: I am not a GCC developer, and therefore this is a complete WAG (wild-ass guess):
My guess would be that GCC always exports template definitions, in order to allow the linker to remove duplicate copies of templates. If it were not exported and more than once source file used that template, the entire source for the
std::map<k, v>class would be duplicated within the two files.I think you're really paying more attention to this than it deserves. Exports are an implementation detail in C++. In C, it makes sense to not export internal functions, so that clients don't come to rely on them. But in C++, the exported functions never have to have anything to do with the source code. One version of GCC's
std::map<k, v>might be completely different from another versions' and as a result the two binaries will not be link-compatible.If you absolutely need portability, export a C interface and ignore the C++ specifics that get exported. Any client of your library trying to call such exports or do anything with them deserves to crash and burn for calling obvious internal implementation details.
EDIT: Made CW because I'm not 100% positive.
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From GCC bug report #36022, which was marked INVALID, Benjamin Kosnik remarked:
[A]n exception class that will be thrown between DSOs must be explicitly marked with default visibility so that the `type_info' nodes will be unified between the DSOs. Thus, the rationale for libstdc++ having namespace std have visibility "default."
Also, looking through the libstdc++ source for
std::map(mine is in/usr/include/c++/4.4.4/bits/stl_map.h), it appears that the way libstdc++ enforces default visibility is with the_GLIBCXX_BEGIN_NESTED_NAMESPACEmacro that is used at the top ofstl_map.h:# define _GLIBCXX_VISIBILITY_ATTR(V) __attribute__ ((__visibility__ (#V))) # define _GLIBCXX_BEGIN_NESTED_NAMESPACE(X, Y) _GLIBCXX_BEGIN_NAMESPACE(X) # define _GLIBCXX_BEGIN_NAMESPACE(X) namespace X _GLIBCXX_VISIBILITY_ATTR(default) {Therefore your STL implementation is explicitly overriding
-fvisibility=hiddenand#pragma GCC visibility push(hidden)/#pragma GCC visibility pop.If you really wanted to force the
std::mapmembers to have hidden visibility then I think you could use something like:// ensure that default visibility is used with any class that is used as an exception type #include <memory> #include <new> #include <stdexcept> // now include the definition of `std::map` using hidden visibility #include <bits/c++config.h> #undef _GLIBCXX_VISIBILITY_ATTR #define _GLIBCXX_VISIBILITY_ATTR(V) __attribute__ ((__visibility__ ("hidden"))) #include <map> #undef _GLIBCXX_VISIBILITY_ATTR #define _GLIBCXX_VISIBILITY_ATTR(V) __attribute__ ((__visibility__ (#V))) // restore `_GLIBCXX_VISIBILITY_ATTR`Then, the following series of commands will verify that the
std::map<int, A>members can be stripped from a shared object:g++ -c -fPIC -fvisibility=hidden test.cppg++ -shared -Wl,-soname,libtest.so.1 -o libtest.so.1.0 test.ostrip -x libtest.so.1.0readelf -s libtest.so.1.0
Note that before step 3,
readelf -s libtest.so.1.0printed (for me):Symbol table '.dynsym' contains 23 entries: Num: Value Size Type Bind Vis Ndx Name 0: 00000000 0 NOTYPE LOCAL DEFAULT UND 1: 00000000 0 NOTYPE WEAK DEFAULT UND __gmon_start__ 2: 00000000 0 NOTYPE WEAK DEFAULT UND _Jv_RegisterClasses 3: 00000000 0 FUNC GLOBAL DEFAULT UND _ZdlPv@GLIBCXX_3.4 (2) 4: 00000000 0 FUNC GLOBAL DEFAULT UND __gxx_personality_v0@CXXABI_1.3 (3) 5: 00000000 0 FUNC GLOBAL DEFAULT UND _Unwind_Resume@GCC_3.0 (4) 6: 00000000 0 FUNC WEAK DEFAULT UND __cxa_finalize@GLIBC_2.1.3 (5) 7: 00000d02 5 FUNC WEAK DEFAULT 12 _ZNSt4pairIKi1AED1Ev 8: 00000d6c 35 FUNC WEAK DEFAULT 12 _ZNSaISt4pairIKi1AEEC1ISt 9: 00000d96 35 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 10: 000023bc 0 NOTYPE GLOBAL DEFAULT ABS _end 11: 000023b4 0 NOTYPE GLOBAL DEFAULT ABS _edata 12: 00000d5e 5 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 13: 000023b4 0 NOTYPE GLOBAL DEFAULT ABS __bss_start 14: 00000bac 5 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 15: 00000d08 35 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 16: 000007f4 0 FUNC GLOBAL DEFAULT 10 _init 17: 00000c4a 35 FUNC WEAK DEFAULT 12 _ZNSaISt13_Rb_tree_nodeIS 18: 00000df8 0 FUNC GLOBAL DEFAULT 13 _fini 19: 00000dba 5 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 20: 00000cde 35 FUNC WEAK DEFAULT 12 _ZNSaISt4pairIKi1AEED1Ev 21: 00000d90 5 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 22: 00000ac6 35 FUNC WEAK DEFAULT 12 _ZNSaISt13_Rb_tree_nodeIS Symbol table '.symtab' contains 84 entries: Num: Value Size Type Bind Vis Ndx Name 0: 00000000 0 NOTYPE LOCAL DEFAULT UND 1: 000000f4 0 SECTION LOCAL DEFAULT 1 2: 00000118 0 SECTION LOCAL DEFAULT 2 3: 000001c0 0 SECTION LOCAL DEFAULT 3 4: 0000022c 0 SECTION LOCAL DEFAULT 4 5: 0000039c 0 SECTION LOCAL DEFAULT 5 6: 000006b6 0 SECTION LOCAL DEFAULT 6 7: 000006e4 0 SECTION LOCAL DEFAULT 7 8: 00000754 0 SECTION LOCAL DEFAULT 8 9: 0000077c 0 SECTION LOCAL DEFAULT 9 10: 000007f4 0 SECTION LOCAL DEFAULT 10 11: 00000824 0 SECTION LOCAL DEFAULT 11 12: 00000930 0 SECTION LOCAL DEFAULT 12 13: 00000df8 0 SECTION LOCAL DEFAULT 13 14: 00000e14 0 SECTION LOCAL DEFAULT 14 15: 00000ef8 0 SECTION LOCAL DEFAULT 15 16: 00001240 0 SECTION LOCAL DEFAULT 16 17: 0000225c 0 SECTION LOCAL DEFAULT 17 18: 00002264 0 SECTION LOCAL DEFAULT 18 19: 0000226c 0 SECTION LOCAL DEFAULT 19 20: 00002270 0 SECTION LOCAL DEFAULT 20 21: 00002358 0 SECTION LOCAL DEFAULT 21 22: 00002364 0 SECTION LOCAL DEFAULT 22 23: 000023ac 0 SECTION LOCAL DEFAULT 23 24: 000023b4 0 SECTION LOCAL DEFAULT 24 25: 00000000 0 SECTION LOCAL DEFAULT 25 26: 00000000 0 FILE LOCAL DEFAULT ABS crtstuff.c 27: 0000225c 0 OBJECT LOCAL DEFAULT 17 __CTOR_LIST__ 28: 00002264 0 OBJECT LOCAL DEFAULT 18 __DTOR_LIST__ 29: 0000226c 0 OBJECT LOCAL DEFAULT 19 __JCR_LIST__ 30: 00000930 0 FUNC LOCAL DEFAULT 12 __do_global_dtors_aux 31: 000023b4 1 OBJECT LOCAL DEFAULT 24 completed.5942 32: 000023b8 4 OBJECT LOCAL DEFAULT 24 dtor_idx.5944 33: 000009b0 0 FUNC LOCAL DEFAULT 12 frame_dummy 34: 00000000 0 FILE LOCAL DEFAULT ABS crtstuff.c 35: 00002260 0 OBJECT LOCAL DEFAULT 17 __CTOR_END__ 36: 0000123c 0 OBJECT LOCAL DEFAULT 15 __FRAME_END__ 37: 0000226c 0 OBJECT LOCAL DEFAULT 19 __JCR_END__ 38: 00000dc0 0 FUNC LOCAL DEFAULT 12 __do_global_ctors_aux 39: 00000000 0 FILE LOCAL DEFAULT ABS test.cpp 40: 00000d64 8 FUNC LOCAL HIDDEN 12 _ZNKSt8_Rb_treeIiSt4pairI 41: 000023b0 4 OBJECT LOCAL HIDDEN 23 DW.ref.__gxx_personality_ 42: 00000b40 11 FUNC LOCAL HIDDEN 12 _ZNSt8_Rb_treeIiSt4pairIK 43: 00000bc8 129 FUNC LOCAL HIDDEN 12 _ZNSt8_Rb_treeIiSt4pairIK 44: 00000bb1 11 FUNC LOCAL HIDDEN 12 _ZNSt8_Rb_treeIiSt4pairIK 45: 00000b4c 96 FUNC LOCAL HIDDEN 12 _ZNSt8_Rb_treeIiSt4pairIK 46: 00000ca0 62 FUNC LOCAL HIDDEN 12 _ZNKSt8_Rb_treeIiSt4pairI 47: 00000ab2 19 FUNC LOCAL HIDDEN 12 _ZNSt8_Rb_treeIiSt4pairIK 48: 00002364 0 OBJECT LOCAL HIDDEN ABS _GLOBAL_OFFSET_TABLE_ 49: 00000a56 92 FUNC LOCAL HIDDEN 12 _ZNSt8_Rb_treeIiSt4pairIK 50: 000009ec 30 FUNC LOCAL HIDDEN 12 _Z11doSomethingv 51: 00000c6e 49 FUNC LOCAL HIDDEN 12 _ZNSt8_Rb_treeIiSt4pairIK 52: 00000a32 35 FUNC LOCAL HIDDEN 12 _ZNSt8_Rb_treeIiSt4pairIK 53: 000023ac 0 OBJECT LOCAL HIDDEN 23 __dso_handle 54: 00000a0a 19 FUNC LOCAL HIDDEN 12 _ZNSt3mapIi1ASt4lessIiESa 55: 00002268 0 OBJECT LOCAL HIDDEN 18 __DTOR_END__ 56: 00000bbc 11 FUNC LOCAL HIDDEN 12 _ZNSt8_Rb_treeIiSt4pairIK 57: 00000a1e 19 FUNC LOCAL HIDDEN 12 _ZNSt3mapIi1ASt4lessIiESa 58: 00000d2c 50 FUNC LOCAL HIDDEN 12 _ZNSt8_Rb_treeIiSt4pairIK 59: 00000aea 85 FUNC LOCAL HIDDEN 12 _ZNSt8_Rb_treeIiSt4pairIK 60: 000009e7 0 FUNC LOCAL HIDDEN 12 __i686.get_pc_thunk.bx 61: 00002270 0 OBJECT LOCAL HIDDEN ABS _DYNAMIC 62: 00000d02 5 FUNC WEAK DEFAULT 12 _ZNSt4pairIKi1AED1Ev 63: 00000c4a 35 FUNC WEAK DEFAULT 12 _ZNSaISt13_Rb_tree_nodeIS 64: 00000000 0 NOTYPE WEAK DEFAULT UND __gmon_start__ 65: 00000000 0 NOTYPE WEAK DEFAULT UND _Jv_RegisterClasses 66: 00000000 0 FUNC GLOBAL DEFAULT UND _ZdlPv@@GLIBCXX_3.4 67: 00000df8 0 FUNC GLOBAL DEFAULT 13 _fini 68: 00000d6c 35 FUNC WEAK DEFAULT 12 _ZNSaISt4pairIKi1AEEC1ISt 69: 00000dba 5 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 70: 00000cde 35 FUNC WEAK DEFAULT 12 _ZNSaISt4pairIKi1AEED1Ev 71: 00000d5e 5 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 72: 00000d90 5 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 73: 000023b4 0 NOTYPE GLOBAL DEFAULT ABS __bss_start 74: 00000d96 35 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 75: 00000bac 5 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 76: 000023bc 0 NOTYPE GLOBAL DEFAULT ABS _end 77: 000023b4 0 NOTYPE GLOBAL DEFAULT ABS _edata 78: 00000ac6 35 FUNC WEAK DEFAULT 12 _ZNSaISt13_Rb_tree_nodeIS 79: 00000000 0 FUNC GLOBAL DEFAULT UND __gxx_personality_v0@@CXX 80: 00000000 0 FUNC GLOBAL DEFAULT UND _Unwind_Resume@@GCC_3.0 81: 00000000 0 FUNC WEAK DEFAULT UND __cxa_finalize@@GLIBC_2.1 82: 00000d08 35 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 83: 000007f4 0 FUNC GLOBAL DEFAULT 10 _initAnd afterward:
Symbol table '.dynsym' contains 23 entries: Num: Value Size Type Bind Vis Ndx Name 0: 00000000 0 NOTYPE LOCAL DEFAULT UND 1: 00000000 0 NOTYPE WEAK DEFAULT UND __gmon_start__ 2: 00000000 0 NOTYPE WEAK DEFAULT UND _Jv_RegisterClasses 3: 00000000 0 FUNC GLOBAL DEFAULT UND _ZdlPv@GLIBCXX_3.4 (2) 4: 00000000 0 FUNC GLOBAL DEFAULT UND __gxx_personality_v0@CXXABI_1.3 (3) 5: 00000000 0 FUNC GLOBAL DEFAULT UND _Unwind_Resume@GCC_3.0 (4) 6: 00000000 0 FUNC WEAK DEFAULT UND __cxa_finalize@GLIBC_2.1.3 (5) 7: 00000d02 5 FUNC WEAK DEFAULT 12 _ZNSt4pairIKi1AED1Ev 8: 00000d6c 35 FUNC WEAK DEFAULT 12 _ZNSaISt4pairIKi1AEEC1ISt 9: 00000d96 35 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 10: 000023bc 0 NOTYPE GLOBAL DEFAULT ABS _end 11: 000023b4 0 NOTYPE GLOBAL DEFAULT ABS _edata 12: 00000d5e 5 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 13: 000023b4 0 NOTYPE GLOBAL DEFAULT ABS __bss_start 14: 00000bac 5 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 15: 00000d08 35 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 16: 000007f4 0 FUNC GLOBAL DEFAULT 10 _init 17: 00000c4a 35 FUNC WEAK DEFAULT 12 _ZNSaISt13_Rb_tree_nodeIS 18: 00000df8 0 FUNC GLOBAL DEFAULT 13 _fini 19: 00000dba 5 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 20: 00000cde 35 FUNC WEAK DEFAULT 12 _ZNSaISt4pairIKi1AEED1Ev 21: 00000d90 5 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 22: 00000ac6 35 FUNC WEAK DEFAULT 12 _ZNSaISt13_Rb_tree_nodeIS Symbol table '.symtab' contains 51 entries: Num: Value Size Type Bind Vis Ndx Name 0: 00000000 0 NOTYPE LOCAL DEFAULT UND 1: 000000f4 0 SECTION LOCAL DEFAULT 1 2: 00000118 0 SECTION LOCAL DEFAULT 2 3: 000001c0 0 SECTION LOCAL DEFAULT 3 4: 0000022c 0 SECTION LOCAL DEFAULT 4 5: 0000039c 0 SECTION LOCAL DEFAULT 5 6: 000006b6 0 SECTION LOCAL DEFAULT 6 7: 000006e4 0 SECTION LOCAL DEFAULT 7 8: 00000754 0 SECTION LOCAL DEFAULT 8 9: 0000077c 0 SECTION LOCAL DEFAULT 9 10: 000007f4 0 SECTION LOCAL DEFAULT 10 11: 00000824 0 SECTION LOCAL DEFAULT 11 12: 00000930 0 SECTION LOCAL DEFAULT 12 13: 00000df8 0 SECTION LOCAL DEFAULT 13 14: 00000e14 0 SECTION LOCAL DEFAULT 14 15: 00000ef8 0 SECTION LOCAL DEFAULT 15 16: 00001240 0 SECTION LOCAL DEFAULT 16 17: 0000225c 0 SECTION LOCAL DEFAULT 17 18: 00002264 0 SECTION LOCAL DEFAULT 18 19: 0000226c 0 SECTION LOCAL DEFAULT 19 20: 00002270 0 SECTION LOCAL DEFAULT 20 21: 00002358 0 SECTION LOCAL DEFAULT 21 22: 00002364 0 SECTION LOCAL DEFAULT 22 23: 000023ac 0 SECTION LOCAL DEFAULT 23 24: 000023b4 0 SECTION LOCAL DEFAULT 24 25: 00000000 0 SECTION LOCAL DEFAULT 25 26: 00000000 0 FILE LOCAL DEFAULT ABS crtstuff.c 27: 00000000 0 FILE LOCAL DEFAULT ABS crtstuff.c 28: 00000000 0 FILE LOCAL DEFAULT ABS test.cpp 29: 00000d02 5 FUNC WEAK DEFAULT 12 _ZNSt4pairIKi1AED1Ev 30: 00000c4a 35 FUNC WEAK DEFAULT 12 _ZNSaISt13_Rb_tree_nodeIS 31: 00000000 0 NOTYPE WEAK DEFAULT UND __gmon_start__ 32: 00000000 0 NOTYPE WEAK DEFAULT UND _Jv_RegisterClasses 33: 00000000 0 FUNC GLOBAL DEFAULT UND _ZdlPv@@GLIBCXX_3.4 34: 00000df8 0 FUNC GLOBAL DEFAULT 13 _fini 35: 00000d6c 35 FUNC WEAK DEFAULT 12 _ZNSaISt4pairIKi1AEEC1ISt 36: 00000dba 5 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 37: 00000cde 35 FUNC WEAK DEFAULT 12 _ZNSaISt4pairIKi1AEED1Ev 38: 00000d5e 5 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 39: 00000d90 5 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 40: 000023b4 0 NOTYPE GLOBAL DEFAULT ABS __bss_start 41: 00000d96 35 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 42: 00000bac 5 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 43: 000023bc 0 NOTYPE GLOBAL DEFAULT ABS _end 44: 000023b4 0 NOTYPE GLOBAL DEFAULT ABS _edata 45: 00000ac6 35 FUNC WEAK DEFAULT 12 _ZNSaISt13_Rb_tree_nodeIS 46: 00000000 0 FUNC GLOBAL DEFAULT UND __gxx_personality_v0@@CXX 47: 00000000 0 FUNC GLOBAL DEFAULT UND _Unwind_Resume@@GCC_3.0 48: 00000000 0 FUNC WEAK DEFAULT UND __cxa_finalize@@GLIBC_2.1 49: 00000d08 35 FUNC WEAK DEFAULT 12 _ZN9__gnu_cxx13new_alloca 50: 000007f4 0 FUNC GLOBAL DEFAULT 10 _initSee also:
- Visibility - GCC Wiki
- Controlling Symbol Visibility
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