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Currently I encountered a weak link issue on Mac OS X 10.6.7 with Xcode 4.0.2. $ gcc --version i686-apple-darwin10-gcc-4.2.1 (GCC) 4.2.1 (Apple Inc. build 5666) (dot 3) As the developer document said , we can use gcc attribute ((weak_import)) for weak link symbol. However, the following sample code always throw compile error. As the following: weak.c : #include <stdlib.h> #include <stdio.h> extern int SayHello() __attribute__((weak)); int main() { int result; if (SayHello!=NULL) { printf("SayHello is present!\n"); result=SayHello(); } else printf("SayHello is not present!\n"); } The error message is the following: $ gcc weak.c Undefined symbols for architecture x86_64: "_f", referenced from: _main in cceOf2wN.o (maybe you meant: __dyld_func_lookup) ld: symbol(s) not found for architecture x86_64 collect2: ld returned 1 exit status Even if use option -undefined dynamic_lookup , it still throws error at runtime: $ gcc -undefined dynamic_lookup weak.c $ ./a.out dyld: Symbol not found: _SayHello Referenced from: /private/tmp/o/./a.out Expected in: dynamic lookup Trace/BPT trap The nm -m message of "a.out" is the following: $ nm -m a.out | grep Hello (undefined) external _SayHello (dynamically looked up) Which was expected as the following: (undefined) weak external _SayHello (dynamically looked up) However, when I compile on Ubuntu with gcc (Ubuntu/Linaro 4.4.4-14ubuntu5) 4.4.5, it works as expected: weak.c : <pre class="l

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