objdump's `--macho` option makes `-M no-aliases` have no effect?

[verhovsky]

I cloned the repo, did cd HelloSilicon/Chapter\ 02, ran make then ran these commands:

objdump -d movexamps
objdump -d -M no-aliases movexamps

objdump -d --macho movexamps
objdump -d --macho -M no-aliases movexamps

These 3

objdump -d movexamps
objdump -d --macho movexamps
objdump -d --macho -M no-aliases movexamps

produce the same disassembly:

$ objdump -d movexamps

movexamps:	file format mach-o arm64

Disassembly of section __TEXT,__text:

0000000100003f7c <_start>:
100003f7c: 42 c7 8d d2 	mov	x2, #28218
100003f80: a2 eb a9 f2 	movk	x2, #20317, lsl #16
100003f84: 82 db df f2 	movk	x2, #65244, lsl #32
100003f88: 82 46 e2 f2 	movk	x2, #4660, lsl #48
100003f8c: e1 03 02 2a 	mov	w1, w2
100003f90: 41 f8 7f d3 	lsl	x1, x2, #1
100003f94: 41 fc 41 d3 	lsr	x1, x2, #1
100003f98: 41 fc 41 93 	asr	x1, x2, #1
100003f9c: 41 04 c2 93 	ror	x1, x2, #1
100003fa0: 01 60 b5 d2 	mov	x1, #2868903936
100003fa4: a1 05 80 12 	mov	w1, #-46
100003fa8: 21 00 80 12 	mov	w1, #-2
100003fac: 00 00 80 d2 	mov	x0, #0
100003fb0: 30 00 80 d2 	mov	x16, #1
100003fb4: 01 10 00 d4 	svc	#0x80
$ objdump -d --macho movexamps
movexamps:
(__TEXT,__text) section
_start:
100003f7c:	42 c7 8d d2	mov	x2, #28218
100003f80:	a2 eb a9 f2	movk	x2, #20317, lsl #16
100003f84:	82 db df f2	movk	x2, #65244, lsl #32
100003f88:	82 46 e2 f2	movk	x2, #4660, lsl #48
100003f8c:	e1 03 02 2a	mov	w1, w2
100003f90:	41 f8 7f d3	lsl	x1, x2, #1
100003f94:	41 fc 41 d3	lsr	x1, x2, #1
100003f98:	41 fc 41 93	asr	x1, x2, #1
100003f9c:	41 04 c2 93	ror	x1, x2, #1
100003fa0:	01 60 b5 d2	mov	x1, #2868903936
100003fa4:	a1 05 80 12	mov	w1, #-46
100003fa8:	21 00 80 12	mov	w1, #-2
100003fac:	00 00 80 d2	mov	x0, #0
100003fb0:	30 00 80 d2	mov	x16, #1
100003fb4:	01 10 00 d4	svc	#0x80
$ objdump -d --macho -M no-aliases movexamps
movexamps:
(__TEXT,__text) section
_start:
100003f7c:	42 c7 8d d2	mov	x2, #28218
100003f80:	a2 eb a9 f2	movk	x2, #20317, lsl #16
100003f84:	82 db df f2	movk	x2, #65244, lsl #32
100003f88:	82 46 e2 f2	movk	x2, #4660, lsl #48
100003f8c:	e1 03 02 2a	mov	w1, w2
100003f90:	41 f8 7f d3	lsl	x1, x2, #1
100003f94:	41 fc 41 d3	lsr	x1, x2, #1
100003f98:	41 fc 41 93	asr	x1, x2, #1
100003f9c:	41 04 c2 93	ror	x1, x2, #1
100003fa0:	01 60 b5 d2	mov	x1, #2868903936
100003fa4:	a1 05 80 12	mov	w1, #-46
100003fa8:	21 00 80 12	mov	w1, #-2
100003fac:	00 00 80 d2	mov	x0, #0
100003fb0:	30 00 80 d2	mov	x16, #1
100003fb4:	01 10 00 d4	svc	#0x80
$ 

Only -M no-aliases without --macho changes any instructions

$ objdump -d -M no-aliases movexamps

movexamps:	file format mach-o arm64

Disassembly of section __TEXT,__text:

0000000100003f7c <_start>:
100003f7c: 42 c7 8d d2 	mov	x2, #28218
100003f80: a2 eb a9 f2 	movk	x2, #20317, lsl #16
100003f84: 82 db df f2 	movk	x2, #65244, lsl #32
100003f88: 82 46 e2 f2 	movk	x2, #4660, lsl #48
100003f8c: e1 03 02 2a 	orr	w1, wzr, w2
100003f90: 41 f8 7f d3 	lsl	x1, x2, #1
100003f94: 41 fc 41 d3 	lsr	x1, x2, #1
100003f98: 41 fc 41 93 	asr	x1, x2, #1
100003f9c: 41 04 c2 93 	extr	x1, x2, x2, #1
100003fa0: 01 60 b5 d2 	mov	x1, #2868903936
100003fa4: a1 05 80 12 	mov	w1, #-46
100003fa8: 21 00 80 12 	mov	w1, #-2
100003fac: 00 00 80 d2 	mov	x0, #0
100003fb0: 30 00 80 d2 	mov	x16, #1
100003fb4: 01 10 00 d4 	svc	#0x80

Although it only changes mov w1, w2 -> orr w1, wzr, w2 and ror x1, x2, #1 -> extr x1, x2, x2, #1. I was promised that

HelloSilicon/Chapter 02/movexamps.s

Lines 37 to 41 in 9fc970d

	// Example of MVN
	MOVN W1, #45
	// Example of a MOV that the Assembler will change to MVN
	MOV W1, #0xFFFFFFFE // (-2)

but it stays the same

100003fa4: a1 05 80 12 	mov	w1, #-46
100003fa8: 21 00 80 12 	mov	w1, #-2

I'm on an M1 Macbook Air, macOS 13.2.1, Xcode version 14.1 (14B47b)

$ as --version
Apple clang version 14.0.0 (clang-1400.0.29.202)
Target: arm64-apple-darwin22.3.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
$ objdump --version
Apple LLVM version 14.0.0 (clang-1400.0.29.202)
  Optimized build.
  Default target: arm64-apple-darwin22.3.0
  Host CPU: apple-a12
[...]
$ softwareupdate --list
Software Update Tool

Finding available software
No new software available.