insert_dylib

Command line utility for inserting a dylib load command into a Mach-O binary.

Does the following (to each arch if the binary is fat):

(Removes LC_CODE_SIGNATURE load command if present)
Adds a LC_LOAD_DYLIB load command to the end of the load commands
Increments the mach header's ncmds and adjusts its sizeofcmds

Usage

Usage: insert_dylib dylib_path binary_path [new_binary_path]
Option flags: --inplace --weak --overwrite --strip-codesig --no-strip-codesig

insert_dylib inserts a load command to load the dylib_path in binary_path.

Unless --inplace option is specified, insert_dylib will produce a new binary at new_binary_path.
If neither --inplace nor new_binary_path is specified, the output binary will be located at the same location as the input binary with _patched prepended to the name.

If the --weak option is specified, insert_dylib will insert a LC_LOAD_WEAK_DYLIB load command instead of LC_LOAD_DYLIB.

Example

$ cat > test.c
int main(void) {
	printf("Testing\n");
	return 0;
}
^D
$ clang test.c -o test &> /dev/null
$ insert_dylib /usr/lib/libfoo.dylib test
The provided dylib path doesn't exist. Continue anyway? [y/n] y
Added LC_LOAD_DYLIB to test_patched
$ ./test
Testing
$ ./test_patched
dyld: Library not loaded: /usr/lib/libfoo.dylib
  Referenced from: /Users/Tyilo/./test_patched
  Reason: image not found
Trace/BPT trap: 5

`otool` `diff` between original and patched binary

$ diff -u <(otool -hl test) <(otool -hl test_patched)
--- /dev/fd/63	2014-07-30 04:08:40.000000000 +0200
+++ /dev/fd/62	2014-07-30 04:08:40.000000000 +0200
@@ -1,7 +1,7 @@
-test:
+test_patched:
 Mach header
       magic cputype cpusubtype  caps    filetype ncmds sizeofcmds      flags
- 0xfeedfacf 16777223          3  0x80          2    16       1296 0x00200085
+ 0xfeedfacf 16777223          3  0x80          2    17       1344 0x00200085
 Load command 0
       cmd LC_SEGMENT_64
   cmdsize 72
@@ -231,3 +231,10 @@
   cmdsize 16
   dataoff 8296
  datasize 64
+Load command 16
+          cmd LC_LOAD_DYLIB
+      cmdsize 48
+         name /usr/lib/libfoo.dylib (offset 24)
+   time stamp 0 Thu Jan  1 01:00:00 1970
+      current version 0.0.0
+compatibility version 0.0.0

`--weak` option

$ insert_dylib --weak /usr/lib/libfoo.dylib test test_patched2
The provided dylib path doesn't exist. Continue anyway? [y/n] y
Added LC_LOAD_WEAK_DYLIB to test_patched2
$ ./test_patched2
Testing

Todo

Improved checking for free space to insert the new load command
Allow removal of LC_CODE_SIGNATURE if it isn't the last load command
Remove __RESTRICT,__restrict if not enough space (suggesion by dirkg)

gwerz/insert_dylib