Validating application of -bind_at_load on OS X

Question

I have a binary that I have linked with the -bind_at_load argument to ld. On an ELF system, I'd use -Wl,-z,now and then readelf to verify that the DT_BIND_NOW flag was enabled on the binary. On OS X, how can I verify that the the appropriate flag in the mach header has been ste to honor -bind_at_load? What is the name of the flag, and what value should it be set to?

Answer 1

You can use otool -l /path/to/binary and inspect the LC_DYLD_INFO_ONLY load command. If the binary was linked with -bind_at_load, then the lazy bind offset/size are equal to 0: dyld won’t lazily bind symbols and all symbols are bound when the binary is loaded.

Sample output:

• With -bind_at_load

  Load command 4
              cmd LC_DYLD_INFO_ONLY
          cmdsize 48
       rebase_off 8192
      rebase_size 8
         bind_off 8200
        bind_size 224
    weak_bind_off 0
   weak_bind_size 0
    lazy_bind_off 0
   lazy_bind_size 0
       export_off 8424
      export_size 48
  

• Without -bind_at_load

  Load command 4
              cmd LC_DYLD_INFO_ONLY
          cmdsize 48
       rebase_off 8192
      rebase_size 8
         bind_off 8200
        bind_size 128
    weak_bind_off 0
   weak_bind_size 0
    lazy_bind_off 8328
   lazy_bind_size 104
       export_off 8432
      export_size 48