Ravi Shekhar Jethani <rsjeth...@gmail.com> writes: > To check this I installed the libgit2-dev package which installed: > /usr/include/git2/*.h , /usr/lib/libgit2.so > Now, I exported all symbols using: > $ readelf -s /usr/lib/libgit2.so > and tried to match these with 'externed' prototypes in the Git source > directory..no matches. > I am confused!!!.
libgit2 is an entirely different package from Git. If you look at the libgit2 sources (https://github.com/libgit2/libgit2), look in include/git2/common.h: /** Declare a public function exported for application use. */ #if __GNUC__ >= 4 # define GIT_EXTERN(type) extern \ __attribute__((visibility("default"))) \ type #elif defined(_MSC_VER) # define GIT_EXTERN(type) __declspec(dllexport) type #else # define GIT_EXTERN(type) extern type #endif I have always used __attribute__((visibility("default"))), but the gcc man page says extern declarations are not affected by -fvisibility, so a lot of code can be recompiled with -fvisibility=hidden with no modifications. However, this means that calls to "extern" functions with no explicit visibility use the PLT, so it is more effective to use "__attribute ((visibility))" and/or "#pragma GCC visibility" to tell the compiler which "extern" declarations should be treated as hidden. However, I don't understand what the first statement means (documentation bug?) since -fvisibility=hidden causes functions declared with 'extern' to be hidden. symbols.c: EXTERN int foo(void); int foo(void) {return 1;} $ gcc -fvisibility=hidden -DEXTERN=extern -shared -o libsymbols.so symbols.c $ nm -D libsymbols.so | grep foo $ meanwhile, $ gcc -fvisibility=hidden -DEXTERN='__attribute((visibility("default")))' -shared -o libsymbols.so symbols.c $ nm -D libsymbols.so | grep foo 000000000000055c T foo > Also I checked this: > $ ldd git > There is no 'gitish' .so in the output; it seems everything is packed > inside one executable. > So your second point 'skipping the PLT...' also doesn't seem to apply here. My comment applied to shared libraries in general, not specifically to Git (which isn't a shared library).
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