feat: app

bin/add_dylib.py

@@ -0,0 +1,98 @@
+#!/usr/bin/env python3
+"""add_dylib.py — Add an LC_LOAD_DYLIB load command to a Mach-O 64-bit binary.
+
+Usage: python3 add_dylib.py <binary> <dylib_path> [--weak]
+
+Inserts the new load command right after the existing load commands, before
+the first section data.  Requires enough free space in the __TEXT header
+region (checked automatically).
+
+The binary is modified in-place; a .orig backup is created first.
+"""
+import struct, sys, shutil, os
+
+LC_LOAD_DYLIB     = 0x0c
+LC_LOAD_WEAK_DYLIB = 0x80000018  # LC_LOAD_WEAK_DYLIB with LC_REQ_DYLD
+
+def main():
+    args = sys.argv[1:]
+    weak = False
+    if '--weak' in args:
+        weak = True
+        args.remove('--weak')
+    if len(args) != 2:
+        sys.exit("Usage: add_dylib.py <binary> <dylib_path> [--weak]")
+    path, dylib = args
+
+    with open(path, 'rb') as f:
+        data = bytearray(f.read())
+
+    # Parse Mach-O 64-bit header
+    magic = struct.unpack_from('<I', data, 0)[0]
+    if magic != 0xfeedfacf:
+        sys.exit(f"Not a 64-bit Mach-O (magic={hex(magic)})")
+
+    cputype, cpusub, filetype, ncmds, sizeofcmds, flags, reserved = \
+        struct.unpack_from('<i i I I I I I', data, 4)
+
+    HEADER_SIZE = 32  # mach_header_64
+    hdr_end = HEADER_SIZE + sizeofcmds
+
+    # Find the earliest section offset (file offset) to know our free space
+    off = HEADER_SIZE
+    min_section_off = len(data)
+    for _ in range(ncmds):
+        cmd, cmdsize = struct.unpack_from('<II', data, off)
+        if cmd == 0x19:  # LC_SEGMENT_64
+            # segment_command_64: cmd(4) cmdsize(4) segname(16) vmaddr(8) vmsize(8) fileoff(8) filesize(8) maxprot(4) initprot(4) nsects(4) flags(4)
+            fileoff = struct.unpack_from('<Q', data, off + 40)[0]   # fileoff at offset 40
+            nsects  = struct.unpack_from('<I', data, off + 64)[0]    # nsects at offset 64
+            sect_off = off + 72  # section_64 array starts at segment + 72
+            for s in range(nsects):
+                sect_fileoff = struct.unpack_from('<I', data, sect_off + s * 80 + 48)[0]
+                if sect_fileoff > 0 and sect_fileoff < min_section_off:
+                    min_section_off = sect_fileoff
+        off += cmdsize
+
+    # Build the LC_LOAD_DYLIB command
+    name = dylib.encode() + b'\0'
+    # name_offset = 24 (cmd + cmdsize + 4*4 for dylib struct)
+    name_offset = 24
+    cmdsize = name_offset + len(name)
+    # align to 8 bytes
+    cmdsize = (cmdsize + 7) & ~7
+
+    needed = cmdsize
+    free = min_section_off - hdr_end
+    if free < needed:
+        sys.exit(f"Not enough free space: need {needed}, have {free} "
+                 f"(hdr_end={hdr_end}, first_section={min_section_off})")
+
+    # Build the command bytes
+    cmd_id = LC_LOAD_WEAK_DYLIB if weak else LC_LOAD_DYLIB
+    cmd = struct.pack('<II', cmd_id, cmdsize)
+    cmd += struct.pack('<IIII', name_offset, 2, 0x10000, 0x10000)  # dylib struct
+    cmd += name
+    cmd += b'\0' * (cmdsize - len(cmd))  # pad to cmdsize
+
+    # Write the new command into existing free space (NO insertion —
+    # the space between sizeofcmds and first section is zero padding).
+    # Inserting bytes would shift all section file offsets and break the binary.
+    data[hdr_end:hdr_end + cmdsize] = cmd
+
+    # Update ncmds and sizeofcmds (in-place, no shift)
+    struct.pack_into('<I', data, 16, ncmds + 1)
+    struct.pack_into('<I', data, 20, sizeofcmds + cmdsize)
+
+    # Backup and write
+    shutil.copy2(path, path + '.orig')
+    with open(path, 'wb') as f:
+        f.write(data)
+
+    print(f"Added {'weak ' if weak else ''}LC_LOAD_DYLIB: {dylib}")
+    print(f"  cmdsize={cmdsize}, ncmds={ncmds}->{ncmds+1}, "
+          f"sizeofcmds={sizeofcmds}->{sizeofcmds+cmdsize}")
+    print(f"  free space was {free} bytes, backup saved as {path}.orig")
+
+if __name__ == '__main__':
+    main()