Add comparator for EFI executables

While investigating why two ostree commits of Endless OS were 120 MB different, despite the only change being an updated Slovenian translation for gnome-control-center, I found that diffoscope cannot compare EFI kernel images. (This was the largest file that different between the two builds.)

file for the EFI kernel image reports:

PE32+ executable (EFI application) x86-64 (stripped to external PDB), for MS Windows

Based on a tip-off on #156, I tried comparing the output of objdump --all-headers --disassemble --line-numbers between the two versions, and this was somewhat informative:

wjt@camille:~$ diff -u <(objdump --all-headers --disassemble --line-numbers old/payg-image.efi) <(objdump --all-headers --disassemble --line-numbers new/payg-image.efi )
--- /dev/fd/63	2020-06-25 13:44:29.736454452 +0100
+++ /dev/fd/62	2020-06-25 13:44:29.736454452 +0100
@@ -1,6 +1,6 @@
 
-old/payg-image.efi:     format de fichier pei-x86-64
-old/payg-image.efi
+new/payg-image.efi:     format de fichier pei-x86-64
+new/payg-image.efi
 architecture: i386:x86-64, fanions 0x00000133:
 HAS_RELOC, EXEC_P, HAS_SYMS, HAS_LOCALS, D_PAGED
 adresse de départ 0x0000000000004000
@@ -15,7 +15,7 @@
 MajorLinkerVersion	2
 MinorLinkerVersion	31
 SizeOfCode		00007800
-SizeOfInitializedData	03cb7000
+SizeOfInitializedData	03cb6c00
 SizeOfUninitializedData	00000000
 AddressOfEntryPoint	0000000000004000
 BaseOfCode		0000000000004000
@@ -31,7 +31,7 @@
 Win32Version		00000000
 SizeOfImage		06153000
 SizeOfHeaders		00000400
-CheckSum		03cc456d
+CheckSum		03cc7d32
 Subsystem		0000000a	(EFI application)
 DllCharacteristics	00000000
 SizeOfStackReserve	0000000000000000
@@ -46,7 +46,7 @@
 Entry 1 0000000000000000 00000000 Import Directory [parts of .idata]
 Entry 2 0000000000000000 00000000 Resource Directory [.rsrc]
 Entry 3 0000000000000000 00000000 Exception Directory [.pdata]
-Entry 4 0000000003cc11a8 000008f8 Security Directory
+Entry 4 0000000003cc0da8 000008f8 Security Directory
 Entry 5 000000000000c000 0000000a Base Relocation Directory [.reloc]
 Entry 6 0000000000000000 00000000 Debug Directory
 Entry 7 0000000000000000 00000000 Description Directory
@@ -85,7 +85,7 @@
                   CONTENTS, ALLOC, LOAD, READONLY, DATA
   8 .linux        00b60830  0000000000040000  0000000000040000  0000ba00  2**2
                   CONTENTS, ALLOC, LOAD, READONLY, DATA
-  9 .initrd       031527c9  0000000003000000  0000000003000000  00b6c400  2**2
+  9 .initrd       03152346  0000000003000000  0000000003000000  00b6c400  2**2
                   CONTENTS, ALLOC, LOAD, READONLY, DATA
 SYMBOL TABLE:
 [  0](sec  1)(fl 0x00)(ty   0)(scl   3) (nx 0) 0x0000000000000028 .exit

The second-largest change between the two images is, indeed, the initramfs, and diffoscope tells me clearly what the problem is:

wjt@camille:~$ docker run --rm -i -w $(pwd) -v $(pwd):$(pwd) registry.salsa.debian.org/reproducible-builds/diffoscope old/initramfs.img new/initramfs.img
--- old/initramfs.img
+++ new/initramfs.img
│┄ comprises of 1 embedded members
├── .cpio file embedded at offset 0
│ ├── file list
│ │ @@ -1,7 +1,7 @@
│ │ -drwxr-xr-x   3        0        0        0 2020-06-23 23:08:12.000000 .
│ │ --rw-r--r--   1        0        0        2 2020-06-23 23:08:12.000000 early_cpio
│ │ -drwxr-xr-x   3        0        0        0 2020-06-23 23:08:12.000000 kernel
│ │ -drwxr-xr-x   3        0        0        0 2020-06-23 23:08:12.000000 kernel/x86
│ │ -drwxr-xr-x   2        0        0        0 2020-06-23 23:08:12.000000 kernel/x86/microcode
│ │ --rw-r--r--   1        0        0    30546 2020-06-23 23:08:12.000000 kernel/x86/microcode/AuthenticAMD.bin
│ │ --rw-r--r--   1        0        0  2860032 2020-06-23 23:08:12.000000 kernel/x86/microcode/GenuineIntel.bin
│ │ +drwxr-xr-x   3        0        0        0 2020-06-24 23:09:16.000000 .
│ │ +-rw-r--r--   1        0        0        2 2020-06-24 23:09:16.000000 early_cpio
│ │ +drwxr-xr-x   3        0        0        0 2020-06-24 23:09:16.000000 kernel
│ │ +drwxr-xr-x   3        0        0        0 2020-06-24 23:09:16.000000 kernel/x86
│ │ +drwxr-xr-x   2        0        0        0 2020-06-24 23:09:16.000000 kernel/x86/microcode
│ │ +-rw-r--r--   1        0        0    30546 2020-06-24 23:09:16.000000 kernel/x86/microcode/AuthenticAMD.bin
│ │ +-rw-r--r--   1        0        0  2860032 2020-06-24 23:09:16.000000 kernel/x86/microcode/GenuineIntel.bin

I believe this is because our dracut is not using --reproducible.

It would be nice if diffoscope could compare EFI executables more neatly than xxd | diff. For extra credit, kernel images with embedded initramfs could be identified and the initramfs compared recursively.