x/arch/arm64/arm64asm: tests fail with new binutils

[mwhudson]

What version of Go are you using (go version)?

1.10 but it doesn't matter.

Does this issue reproduce with the latest release?

Yes.

What operating system and processor architecture are you using (go env)?

Ubuntu 18.10 on arm64.

What did you do?

$ go test golang.org/x/arch/arm64/arm64asm

What did you expect to see?

tests passing

What did you see instead?

--- FAIL: TestObjdumpARM64TestDecodeGNUSyntaxdata (0.48s)
	ext_test.go:197: decode(9f3003d5) = "dsb #0x00", 4, want "ssbb", 4
		
	ext_test.go:197: decode(9f3403d5) = "dsb #0x04", 4, want "pssbb", 4
		
	ext_test.go:203: 4651 test cases, 933 expected mismatches, 2 failures; 19612 cases/second
	ext_test.go:204: decoder coverage: 96.4%;
	ext_test.go:203: 4651 test cases, 0 expected mismatches, 0 failures; 20158 cases/second
	ext_test.go:204: decoder coverage: 96.4%;
--- FAIL: TestObjdumpARM64TestDecodeGoSyntaxdata (0.47s)
	ext_test.go:197: decode(9f3003d5) = "dsb #0x00", 4, want "ssbb", 4
		
	ext_test.go:197: decode(9f3403d5) = "dsb #0x04", 4, want "pssbb", 4
		
	ext_test.go:203: 4564 test cases, 964 expected mismatches, 2 failures; 19893 cases/second
	ext_test.go:204: decoder coverage: 96.4%;
	ext_test.go:203: 4564 test cases, 0 expected mismatches, 0 failures; 20033 cases/second
	ext_test.go:204: decoder coverage: 96.4%;
FAIL
FAIL	golang.org/x/arch/arm64/arm64asm	5.308s

[mwhudson]

I think what's going on here is that the new binutils in this version of Ubuntu supports some new mnemonics. I presume the fix is to adjust allowedMismatchObjdump to accept both forms, I'll submit a CL to implement this soon but I'm a bit busy today.

[cherrymui]

Yeah, I think this is the cause. Is there some flags to objdump to make it prefer old instruction names? If so, we probably want to use that so the test is more tolerable to new objdump changes.

[mwhudson]

You can pass -M no-aliases to, I think, suppress all mnemonics but that's probably going too far.

[gopherbot]

Change https://golang.org/cl/136455 mentions this issue: arm64/arm64asm: recognise new ssbb/pssbb mnemonics from objdump