Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

x/arch: incorrect disassembly for x86 FMA instruction #41043

Open
zhangyoufu opened this issue Aug 26, 2020 · 1 comment
Open

x/arch: incorrect disassembly for x86 FMA instruction #41043

zhangyoufu opened this issue Aug 26, 2020 · 1 comment
Labels
NeedsInvestigation
Milestone

Comments

@zhangyoufu
Copy link
Contributor

@zhangyoufu zhangyoufu commented Aug 26, 2020

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

$ go version
go version go1.15 darwin/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
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/zhangyoufu/Library/Caches/go-build"
GOENV="/Users/zhangyoufu/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/zhangyoufu/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/zhangyoufu/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/Cellar/go/1.15/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.15/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/vf/10556_c97vj8qmvw000tgh5w0000gn/T/go-build228934958=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Sample:

package main

import (
	"log"
	"math"
)

func main() {
	log.Print(math.FMA(0, 0, 0))
}
$ go tool compile -S a.go | head -n 20
"".main STEXT size=183 args=0x0 locals=0x38
	0x0000 00000 (a.go:8)	TEXT	"".main(SB), ABIInternal, $56-0
	0x0000 00000 (a.go:8)	MOVQ	(TLS), CX
	0x0009 00009 (a.go:8)	CMPQ	SP, 16(CX)
	0x000d 00013 (a.go:8)	PCDATA	$0, $-2
	0x000d 00013 (a.go:8)	JLS	173
	0x0013 00019 (a.go:8)	PCDATA	$0, $-1
	0x0013 00019 (a.go:8)	SUBQ	$56, SP
	0x0017 00023 (a.go:8)	MOVQ	BP, 48(SP)
	0x001c 00028 (a.go:8)	LEAQ	48(SP), BP
	0x0021 00033 (a.go:8)	FUNCDATA	$0, gclocals·69c1753bd5f81501d95132d08af04464(SB)
	0x0021 00033 (a.go:8)	FUNCDATA	$1, gclocals·568470801006e5c0dc3947ea998fe279(SB)
	0x0021 00033 (a.go:8)	FUNCDATA	$3, "".main.stkobj(SB)
	0x0021 00033 (a.go:8)	MOVBQZX	runtime.x86HasFMA(SB), AX
	0x0029 00041 (a.go:8)	TESTQ	AX, AX
	0x002c 00044 (a.go:9)	JEQ	136
	0x002e 00046 (a.go:9)	XORPS	X0, X0
	0x0031 00049 (a.go:9)	VFMADD231SD	X0, X0, X0
	0x0036 00054 (a.go:9)	XORPS	X1, X1
	0x0039 00057 (a.go:9)	MOVUPS	X1, ""..autotmp_1+32(SP)
go tool compile: signal: broken pipe
$ go build a.go
$ go tool objdump -s main.main a | head -n13
TEXT main.main(SB) /Users/zhangyoufu/a.go
  a.go:8		0x10a8760		65488b0c2530000000	MOVQ GS:0x30, CX
  a.go:8		0x10a8769		483b6110		CMPQ 0x10(CX), SP
  a.go:8		0x10a876d		0f869a000000		JBE 0x10a880d
  a.go:8		0x10a8773		4883ec38		SUBQ $0x38, SP
  a.go:8		0x10a8777		48896c2430		MOVQ BP, 0x30(SP)
  a.go:8		0x10a877c		488d6c2430		LEAQ 0x30(SP), BP
  a.go:8		0x10a8781		480fb6054b710f00	MOVZX runtime.x86HasFMA(SB), AX
  a.go:8		0x10a8789		4885c0			TESTQ AX, AX
  a.go:9		0x10a878c		745a			JE 0x10a87e8
  a.go:9		0x10a878e		0f57c0			XORPS X0, X0
  a.go:9		0x10a8791		c4e2f9b9c00f57c9	MOVL $-0x36a8f040, CX
  a.go:9		0x10a8799		0f114c2420		MOVUPS X1, 0x20(SP)

What did you expect to see?

objdump shows FMA instruction VFMADD231SD X0, X0, X0.

What did you see instead?

objdump shows MOVL $-0x36a8f040, CX

@cagedmantis cagedmantis added this to the Backlog milestone Aug 26, 2020
@cagedmantis cagedmantis added the NeedsInvestigation label Aug 26, 2020
@cagedmantis
Copy link
Contributor

@cagedmantis cagedmantis commented Aug 26, 2020

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Labels
NeedsInvestigation
Projects
None yet
Development

No branches or pull requests

2 participants