nm symbol output t vs T in a shared so library

Question

I have added a new function (fuse_lowlevel_notify_inval_directory) in user space fuse library. The compilation and creation of libfuse.so is finished without error. But when my application tries to use this new function, the linker is throwing error: undefined reference to `fuse_lowlevel_notify_inval_directory' collect2: ld returned 1 exit status

When I checked with nm

nm ../libfuse.so | grep inval
00000000000154ed T fuse_invalidate
**000000000001e142 t fuse_lowlevel_notify_inval_directory**
000000000001e26c T fuse_lowlevel_notify_inval_entry
000000000001e1cb T fuse_lowlevel_notify_inval_inode

T/t means the symbol is present in text section. if uppercase, the symbol is global (external). I suspect this is the issue. The new added function is showing lowercase t while other older functions are having upper case T. Any idea about what I might be doing wrong?

Answer 1

Any idea about what I might be doing wrong?

The t function is indeed local to the library. This could happen due to a number or reasons. The most likely ones are:

1. You declared the function static, or
2. You compiled the library with -fvisibility=hidden and did not have __attribute__((visibility("default"))) on the function, or
3. You linked this library with a linker version script (i.e. with --version-script=libfoo.version flag) that hides all functions, except those which are explicitly exported, and you didn't add your function to that list.
   
   See this example of using --version-script to limit symbol visibility.