cmd/link: -buildmode=pie -linkshared panic at runtime

[kiap]

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

$ go version

go version go1.17 linux/amd64

Does this issue reproduce with the latest release?

Yes

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

Linux x86_64 both CentOS 7.9 and RHEL 8.4

go env Output

$ go env
GO111MODULE=""

GOARCH="amd64"

GOBIN=""

GOCACHE="/usr/src/.cache"

GOENV="/root/.config/go/env"

GOEXE=""

GOEXPERIMENT=""

GOFLAGS=""

GOHOSTARCH="amd64"

GOHOSTOS="linux"

GOINSECURE=""

GOMODCACHE="/usr/src/dev/pkg/mod"

GONOPROXY=""

GONOSUMDB=""

GOOS="linux"

GOPATH="/usr/src/dev"

GOPRIVATE=""

GOPROXY="https://proxy.golang.org,direct"

GOROOT="/usr/src/dev"

GOSUMDB="sum.golang.org"

GOTMPDIR=""

GOTOOLDIR="/usr/src/dev/pkg/tool/linux_amd64"

GOVCS=""

GOVERSION="go1.17"

GCCGO="gccgo"

AR="ar"

CC="gcc"

CXX="g++"

CGO_ENABLED="1"

GOMOD="/usr/src/dev/src/hello/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-build919601769=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Building a simple hello program with shared library

go install -v -ldflags '-s -w' -buildmode=shared -linkshared -pkgdir /usr/src/lib std
go install -v -ldflags '-s -w' -buildmode=pie -linkshared -pkgdir /usr/src/lib hello

package main

import  (
              "fmt"
)
func main() {
           fmt.Printf("Hello, World!\n")
}

What did you expect to see?

Hello, World!

What did you see instead?

fatal error: unreachable method called. linker bug?

goroutine 1 [running]:
runtime.throw({0x7f77de5db273, 0xc00034c708})
/usr/src/dev/src/runtime/panic.go:1198 +0x71 fp=0xc00035aeb8 sp=0xc00035ae88 pc=0x7f77ddead251
runtime.unreachableMethod()
/usr/src/dev/src/runtime/iface.go:561 +0x25 fp=0xc00035aed8 sp=0xc00035aeb8 pc=0x7f77dde77ea5
fmt.Fprintf({0x5616a7877b48, 0xc0003ae008}, {0x5616a76771e0, 0xe}, {0x0, 0x0, 0x0})
/usr/src/dev/src/fmt/print.go:205 +0x9b fp=0xc00035af38 sp=0xc00035aed8 pc=0x7f77ddfc0ddb
fmt.Printf(...)
/usr/src/dev/src/fmt/print.go:213
()
src/hello/hello.go:10 +0x3e fp=0xc00035af80 sp=0xc00035af38 pc=0x5616a767711e
runtime.main()
/usr/src/dev/src/runtime/proc.go:255 +0x282 fp=0xc00035afe0 sp=0xc00035af80 pc=0x7f77ddeb0902
runtime.goexit()
/usr/src/dev/src/runtime/asm_amd64.s:1581 +0x1 fp=0xc00035afe8 sp=0xc00035afe0 pc=0x7f77ddee93a1

[toothrot]

Possibly related: #25970

@ianlancetaylor @cherrymui

[zhouguangyuan0718]

Function fmt.Printf is inlined. The actually called function is fmt.Fprintf, and the first arg is an ifcae, the data of it is os.Stdout. the tab of it is go.itab.*os.File,io.Writer.
I add flag "-dumpdep" to linker:

_ -> main.main
_ -> main..inittask
_ -> runtime.unreachableMethod
main.main -> os.Stdout
main.main -> go.itab.*os.File,io.Writer
main.main -> go.string."Hello, World!\n"
main.main -> fmt.Fprintf
main.main -> runtime.morestack_noctxt
main.main -> gclocals·33cdeccccebe80329f1fdbee7f5874cb
 -> go.info.fmt.Printf$abstract
go.itab.*os.File,io.Writer -> type.io.Writer
go.itab.*os.File,io.Writer -> type.*os.File 
main..inittask -> fmt..inittask
go.info.fmt.Printf$abstract -> go.info.string
go.info.fmt.Printf$abstract -> go.info.[]interface {}
go.info.fmt.Printf$abstract -> go.info.int
go.info.fmt.Printf$abstract -> go.info.error

It shows that type.*os.File is marked as "UsedInIface" in deadcode. But the symbol "type.*os.File" is in libstd.so. the method 'Write' of type.*os.File don't be marked as reachable. So the field fun of 'go.itab.*os.File,io.Writer' will be a weak reference. In function relocsym, the fun of 'go.itab.*os.File,io.Writer' will be reloced to "runtime.unreachableMethod"
It seems like this appears after https://go-review.googlesource.com/c/go/+/268479

[gopherbot]

Change https://golang.org/cl/350189 mentions this issue: cmd/link: disable weak reference in itab if build with "-linkshared"

[zhouguangyuan0718]

Can you review this CL when you're free?
This cl is blocking our project. If this cl can be approved, we will cherry-pick this to our own golang-1.17.
@ianlancetaylor @cherrymui

[zhouguangyuan0718]

@gopherbot please consider this for backport to 1.17, maybe we need fix it for 1.17.

[gopherbot]

Backport issue(s) opened: #49086 (for 1.17).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://golang.org/wiki/MinorReleases.