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When GOARCH is set to mipsle, sync/atomic.Loadint64 will prompt "invalid memory address or nil pointer dereference" when sync.WaitGroup exists in the structure #41970

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ssoor opened this issue Oct 14, 2020 · 2 comments

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@ssoor
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@ssoor ssoor commented Oct 14, 2020

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

$ go version
go version go1.15 linux/amd64

yum package(Repository: epel):

golang-src-1.15.2-1.el7.noarch
golang-bin-1.15.2-1.el7.x86_64
golang-1.15.2-1.el7.x86_64
golang-misc-1.15.2-1.el7.noarch

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="on"
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/core/.cache/go-build"
GOENV="/home/core/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/mnt/source_code/golang/pkg/mod"
GOOS="linux"
GOPATH="/mnt/source_code/golang/"
GOPROXY="https://goproxy.cn,direct"
GOROOT="/home/core/.go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/core/.go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/mnt/source_code/golang/src/github.com/ssoor/test/go.mod"
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 -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build294050133=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Build(x86):

$GOOS=linux GOARCH=mipsle GOMIPS=softfloat go build-o testRun
$scp testRun root@xxxxxx:~/gogs/testRun

Run(mips):

$ ./testRun
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x11b30]

goroutine 1 [running]:
runtime/internal/atomic.lockAndCheck(...)
        /home/core/.go/src/runtime/internal/atomic/atomic_mipsx.go:40
runtime/internal/atomic.Load64(0x81404c, 0x814040, 0x15060)
        /home/core/.go/src/runtime/internal/atomic/atomic_mipsx.go:93 +0x20
main.main()
        /mnt/source_code/golang/src/github.com/ssoor/test/main.go:23 +0x54

Source:

package main

import (
	"fmt"
	"sync"
	"sync/atomic"
)

type TestStruct struct {
	wgClose        sync.WaitGroup // When it exists, it will report an error, comment out it is normal
	requestTimeout int64
}

func main() {
	testV := TestStruct{}
	fmt.Println(atomic.LoadInt64(&testV.requestTimeout))
}

What did you expect to see?

0

What did you see instead?

panic: runtime error: invalid memory address or nil pointer dereference
@davecheney
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@davecheney davecheney commented Oct 14, 2020

Switch the order of the fields in the struct. See #599

@rsc
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@rsc rsc commented Oct 14, 2020

https://golang.org/pkg/sync/atomic/#pkg-note-BUG explains:

On ARM, x86-32, and 32-bit MIPS, it is the caller's responsibility to arrange for 64-bit alignment of 64-bit words accessed atomically. The first word in a variable or in an allocated struct, array, or slice can be relied upon to be 64-bit aligned.

We are working to fix this (#36606) but for now the solution is to put atomically accessed 64-bit fields at the start of the struct to guarantee 64-bit alignment.

@rsc rsc closed this Oct 14, 2020
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