Dumping memory to file with LLDB

Suppose we would like to dump byte buffer managed by Data instance, which is our case is UTF8 encoded string representation.

(lldb) po data
▿ 1278 bytes
  - count : 1278
  ▿ pointer : 0x00007ff5fc861800
    - pointerValue : 140694480361472

The following command will read¹ 1278 bytes starting at 0x00007ff5fc861800 and save command output to file at specified path.

(lldb) memory read --force --count 1278 --outfile /Users/wojtek/data.hexdump 0x00007ff5fc861800

The file format is quite similar to the one used by xxd². The only difference is that xxd hexdump format does not precede address with 0x.

% head -n 4 data.hexdump
0x7ff5fc861800: 4c 6f 72 65 6d 20 69 70 73 75 6d 20 64 6f 6c 6f  Lorem ipsum dolo
0x7ff5fc861810: 72 20 73 69 74 20 61 6d 65 74 2c 20 63 6f 6e 73  r sit amet, cons
0x7ff5fc861820: 65 63 74 65 74 75 72 20 61 64 69 70 69 73 63 69  ectetur adipisci
0x7ff5fc861830: 6e 67 20 65 6c 69 74 2e 20 49 6e 20 61 63 20 63  ng elit. In ac c

Conversion is trivial, we need to remove first two bytes in every line.

% cut -b 3- data.hexdump > data.xxd

% head -n 4 data.xxd
7ff5fc861800: 4c 6f 72 65 6d 20 69 70 73 75 6d 20 64 6f 6c 6f  Lorem ipsum dolo
7ff5fc861810: 72 20 73 69 74 20 61 6d 65 74 2c 20 63 6f 6e 73  r sit amet, cons
7ff5fc861820: 65 63 74 65 74 75 72 20 61 64 69 70 69 73 63 69  ectetur adipisci
7ff5fc861830: 6e 67 20 65 6c 69 74 2e 20 49 6e 20 61 63 20 63  ng elit. In ac c

Finally we can proceed with hexdump to binary conversion. Note that we need to tell xxd not to write 0x7ff5fc861800 bytes of zeros before starting to write the actual data.

% xxd -revert -groupsize 1 --seek -0x7ff5fc861800 data.xxd data.txt