On Mon, 02 May 2011 17:24:53 +0200, Kevin Kofler wrote: > Jan Kratochvil wrote: > > There is the STT_GNU_IFUNC feature implemented for it - the indirect is > > handled by linker without an additional indirect overhead if applied for a > > shared library function. For apps it works in a similar way as normal > > indirect. > > Are there any caveats (initialization order or so) when using this feature? Yes, a bit. STT_GNU_IFUNC relocations are sorted as last in the library to be relocated. But still they are called before any static initializers (static constructors), the sample code below outputs: resolver constructor main func1 destructor > E.g. would one get away with calling something like > http://api.kde.org/4.0-api/kdelibs-apidocs/solid/html/tutorial3.html (i.e. > Solid::Processor::instructionSets) in the ifunc or would trying to call such > C++ classes lead to errors or unpredictable behavior? Unless there are static initializers it should work. > And I presume this is available on ELF glibc targets only, isn't it? It is GNU/Linux feature, unrelated to glibc (glibc is just one of its users). STT_GNU_IFUNC is ELF feature and it is in STT_LOOS..STT_HIOS, therefore it needs ELFOSABI_LINUX. Thanks, Jan ------------------------------------------------------------------------------ #include <stdio.h> #include <time.h> class C { public: C() { puts ("constructor"); } ~C() { puts ("destructor"); } } c; static void func1 (void) { puts ("func1"); } static void func2 (void) { puts ("func2"); } typedef void (*func_t) (void); asm (".type _Z9gnu_ifuncv, @gnu_indirect_function"); func_t gnu_ifunc (void) { puts ("resolver"); return time (NULL) & 1 ? func1 : func2; } int main (void) { puts ("main"); gnu_ifunc (); return 0; } -- devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxxx https://admin.fedoraproject.org/mailman/listinfo/devel
