cmd/asm: amd64: Invalid instruction emits wrong binary without error

[bupjae]

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

$ go version
go version go1.20.3 windows/amd64

Does this issue reproduce with the latest release?

Yes

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

go env Output

$ go env
set GO111MODULE=
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\Bupjae\AppData\Local\go-build
set GOENV=C:\Users\Bupjae\AppData\Roaming\go\env
set GOEXE=.exe
set GOEXPERIMENT=
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOINSECURE=
set GOMODCACHE=C:\Users\Bupjae\go\pkg\mod
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\Bupjae\go
set GOPRIVATE=
set GOPROXY=https://proxy.golang.org,direct
set GOROOT=D:\BupProg\OldGoTest\go\go1.20.3
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLDIR=D:\BupProg\OldGoTest\go\go1.20.3\pkg\tool\windows_amd64
set GOVCS=
set GOVERSION=go1.20.3
set GCCGO=gccgo
set GOAMD64=v1
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=NUL
set GOWORK=
set CGO_CFLAGS=-O2 -g
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-O2 -g
set CGO_FFLAGS=-O2 -g
set CGO_LDFLAGS=-O2 -g
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=C:\Users\Bupjae\AppData\Local\Temp\go-build1676784847=/tmp/go-build -gno-record-gcc-switches

What did you do?

Created demo.s then go build

#include "textflag.h"

TEXT ·foo(SB), NOSPLIT, $0-0
MOVB AH, R8
RET

What did you expect to see?

Build failed with suitable error message. (i.e. asm: "".foo: invalid instruction).

According to Intel® 64 and IA-32 Architectures Software Developer's Manuals, register AH cannot be used if REX prefix is used. Using register R8 needs REX prefix.

What did you see instead?

Build was successful. Disassembling shows following:

000000000045c8a0 <main.foo.abi0>:
  45c8a0:	41 88 e0             	mov    %spl,%r8b
  45c8a3:	c3                   	retq   

[randall77]

Dup of #45511 or #14288 ?

[bupjae]

I agree that this issue is dup of #14288. Closing.