I am new to MacOS & MacOS programming. I would like to know how an application is working (by simply having a glimpse of the binary's imported system APIs for learning).
I tried otool, printed the help message, I saw the message says -L prints the shared libraries used. Then I ran otool -L <binary-file>, but it only printed the names of the used libraries, without any imported symbols.
Maybe I missed something in otool, or is there any other tool that can help get import symbols in a mach-o binary?
You can get a simple list of imported symbols with nm -u:
% nm -u /bin/echo
___mb_cur_max
___stdoutp
_err
_exit
_fflush
_getenv
_mbtowc
_putchar
_putwchar
_strcmp
_strlen
dyld_stub_binder
For more detailed information, including the library that each symbol is expected to come from, you can use dyldinfo. This requires Xcode though, and has to be invoked as xcrun dyldinfo. You'll want the union of -bind, -weak_bind and -lazy_bind:
% xcrun dyldinfo -bind /bin/echo
bind information:
segment section address type addend dylib symbol
__DATA_CONST __got 0x100004000 pointer 0 libSystem ___mb_cur_max
__DATA_CONST __got 0x100004008 pointer 0 libSystem ___stdoutp
__DATA_CONST __got 0x100004010 pointer 0 libSystem dyld_stub_binder
% xcrun dyldinfo -weak_bind /bin/echo
no weak binding
% xcrun dyldinfo -lazy_bind /bin/echo
lazy binding information (from lazy_bind part of dyld info):
segment section address index dylib symbol
__DATA __la_symbol_ptr 0x100008000 0x0000 libSystem _err
__DATA __la_symbol_ptr 0x100008008 0x000B libSystem _exit
__DATA __la_symbol_ptr 0x100008010 0x0017 libSystem _fflush
__DATA __la_symbol_ptr 0x100008018 0x0025 libSystem _getenv
__DATA __la_symbol_ptr 0x100008020 0x0033 libSystem _mbtowc
__DATA __la_symbol_ptr 0x100008028 0x0041 libSystem _putchar
__DATA __la_symbol_ptr 0x100008030 0x0050 libSystem _putwchar
__DATA __la_symbol_ptr 0x100008038 0x0060 libSystem _strcmp
__DATA __la_symbol_ptr 0x100008040 0x006E libSystem _strlen