runtime: darwin using -buildmode=c-shared so got runtime: unexpected return pc for runtime.sigpanic called from 0x41e745a

[wangzz719]

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

$ go version
go version go1.14.4 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/wangzhizhao/Library/Caches/go-build"
GOENV="/Users/wangzhizhao/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GONOPROXY="*.byted.org,*.everphoto.cn"
GONOSUMDB="*.byted.org,*.everphoto.cn"
GOOS="darwin"
GOPATH="/Users/wangzhizhao/go"
GOPRIVATE="*.byted.org,*.everphoto.cn"
GOPROXY="https://go-mod-proxy.byted.org,https://goproxy.cn,https://proxy.golang.org,direct"
GOROOT="/usr/local/go"
GOSUMDB="sum.golang.google.cn"
GOTMPDIR=""
GOTOOLDIR="/usr/local/go/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/wangzhizhao/go/src/goscripts/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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/c5/gc9h916j1578f82zvg1hgxf40000gp/T/go-build852002820=/tmp/go-build -gno-record-gcc-switches -fno-common"

uname -a Output

$uname -a
Darwin wangzhizhaodeMacBook-Pro.local 18.7.0 Darwin Kernel Version 18.7.0: Mon Apr 27 20:09:39 PDT 2020; root:xnu-4903.278.35~1/RELEASE_X86_64 x86_64

What did you do?

1. source code is the following two files:
   verify.go

package main

// #include <stdlib.h>
import "C"

import (
	"encoding/hex"
	"strings"

	"verify/sec"
)

//export Verify
func Verify(serviceNameC *C.char, keyC *C.char) *C.char {
	serviceName := C.GoString(serviceNameC)

	key := []byte(C.GoString(keyC))
	sec.InitWithKey(key)

	res := "res"
	return C.CString(strings.Join([]string{serviceName, res, hex.EncodeToString(key)}, "-"))
}

func main() {

}

sec/key.go

package sec

import (
	"encoding/hex"
	"fmt"
)

var CryptoKey []byte

func InitWithKey(key []byte) {
	CryptoKey = key
	fmt.Println(hex.EncodeToString(key))
}

2. go build genrate c-shared .so
   go build -buildmode=c-shared -a -o libverify.so verify.go

3. using libverify.so

package main

// #cgo LDFLAGS: -lverify
// #include </usr/local/lib/verify.h>
import "C"
import (
	"fmt"
	"unsafe"
)

func freeCString(cString *C.char) {
	C.free(unsafe.Pointer(cString))
}

func Init(serviceName string) {
	cServiceName := C.CString(serviceName)
	defer freeCString(cServiceName)
	key := C.CString("test")
	defer freeCString(key)

	cRes := C.Verify(cServiceName, key)
	defer freeCString(cRes)

	fmt.Println(C.GoString(cRes))
}

func main() {
	Init("my-service")
}

What did you expect to see?

no panic, and print out a string.

What did you see instead?

fatal error: unexpected signal during runtime execution
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x41e745a]

goroutine 1 [running, locked to thread]:
runtime.throw(0x40d653d, 0x2a)
	/usr/local/go/src/runtime/panic.go:1116 +0x72 fp=0xc0000439b0 sp=0xc000043980 pc=0x4030dd2
runtime: unexpected return pc for runtime.sigpanic called from 0x41e745a
stack: frame={sp:0xc0000439b0, fp:0xc0000439e0} stack=[0xc000043000,0xc000044000)
000000c0000438b0:  0000000000000000  0000000000000000
000000c0000438c0:  0000000000000000  0000000000000000
000000c0000438d0:  0000000000000000  0000000000000000
000000c0000438e0:  0000000000000000  0000000000000000
000000c0000438f0:  0000000000000000  0000000000000000
000000c000043900:  0000000000000000  0000000000000000
000000c000043910:  0000000000000000  0000000000000000
000000c000043920:  0000000000000000  0000000000000000
000000c000043930:  0000000000000000  0000000000000000
000000c000043940:  0000000004030f97 <runtime.fatalthrow+87>  000000c000043950
000000c000043950:  000000000405a860 <runtime.fatalthrow.func1+0>  000000c000000180
000000c000043960:  0000000004030dd2 <runtime.throw+114>  000000c000043980
000000c000043970:  000000c0000439a0  0000000004030dd2 <runtime.throw+114>
000000c000043980:  000000c000043988  000000000405a7e0 <runtime.throw.func1+0>
000000c000043990:  00000000040d653d  000000000000002a
000000c0000439a0:  000000c0000439d0  0000000004044f2a <runtime.sigpanic+1130>
000000c0000439b0: <00000000040d653d  000000000000002a
000000c0000439c0:  0000000000000000  0000000000000000
000000c0000439d0:  000000c000043aa8 !00000000041e745a
000000c0000439e0: >0000000000000000  0000000000000000
000000c0000439f0:  0000000000000000  0000000000000000
000000c000043a00:  0000000000000000  0000000000000000
000000c000043a10:  0000000000000000  0000000000000000
000000c000043a20:  000802aaaa00aaaa  0000000000000034
000000c000043a30:  0000000000000020  0000000000000000
000000c000043a40:  0000000000000000  0000000000000000
000000c000043a50:  0000000000000000  0000000000203000
000000c000043a60:  0000000000203000  0000000000203000
000000c000043a70:  0000000000000000  0000000000000000
000000c000043a80:  0000000000000008  0000000000000000
000000c000043a90:  0000000000000000  000000c000043b38
000000c000043aa0:  000000000400d726 <runtime.mallocgc+790>  000000c000043b48
000000c000043ab0:  00000000041df53e  000000c000012200
000000c000043ac0:  0000000000000010  0000000000000010
000000c000043ad0:  0000000004281340  0000000000000680
runtime.sigpanic()
	/usr/local/go/src/runtime/signal_unix.go:679 +0x46a fp=0xc0000439e0 sp=0xc0000439b0 pc=0x4044f2a

goroutine 2 [force gc (idle)]:
runtime.gopark(0x40d7b98, 0x417f670, 0x1411, 0x1)
	/usr/local/go/src/runtime/proc.go:304 +0xe0 fp=0xc000030fb0 sp=0xc000030f90 pc=0x40337f0
runtime.goparkunlock(...)
	/usr/local/go/src/runtime/proc.go:310
runtime.forcegchelper()
	/usr/local/go/src/runtime/proc.go:253 +0xb7 fp=0xc000030fe0 sp=0xc000030fb0 pc=0x40336a7
runtime.goexit()
	/usr/local/go/src/runtime/asm_amd64.s:1373 +0x1 fp=0xc000030fe8 sp=0xc000030fe0 pc=0x405da91
created by runtime.init.6
	/usr/local/go/src/runtime/proc.go:242 +0x35

goroutine 18 [GC sweep wait]:
runtime.gopark(0x40d7b98, 0x417f7a0, 0x140c, 0x1)
	/usr/local/go/src/runtime/proc.go:304 +0xe0 fp=0xc00002c7a8 sp=0xc00002c788 pc=0x40337f0
runtime.goparkunlock(...)
	/usr/local/go/src/runtime/proc.go:310
runtime.bgsweep(0xc00008e000)
	/usr/local/go/src/runtime/mgcsweep.go:70 +0x9c fp=0xc00002c7d8 sp=0xc00002c7a8 pc=0x4021a4c
runtime.goexit()
	/usr/local/go/src/runtime/asm_amd64.s:1373 +0x1 fp=0xc00002c7e0 sp=0xc00002c7d8 pc=0x405da91
created by runtime.gcenable
	/usr/local/go/src/runtime/mgc.go:214 +0x5c

goroutine 19 [GC scavenge wait]:
runtime.gopark(0x40d7b98, 0x417f760, 0x140d, 0x1)
	/usr/local/go/src/runtime/proc.go:304 +0xe0 fp=0xc00002cf78 sp=0xc00002cf58 pc=0x40337f0
runtime.goparkunlock(...)
	/usr/local/go/src/runtime/proc.go:310
runtime.bgscavenge(0xc00008e000)
	/usr/local/go/src/runtime/mgcscavenge.go:237 +0xd0 fp=0xc00002cfd8 sp=0xc00002cf78 pc=0x401ffa0
runtime.goexit()
	/usr/local/go/src/runtime/asm_amd64.s:1373 +0x1 fp=0xc00002cfe0 sp=0xc00002cfd8 pc=0x405da91
created by runtime.gcenable
	/usr/local/go/src/runtime/mgc.go:215 +0x7e

goroutine 3 [finalizer wait]:
runtime.gopark(0x40d7b98, 0x41a8ca8, 0x1410, 0x1)
	/usr/local/go/src/runtime/proc.go:304 +0xe0 fp=0xc000030758 sp=0xc000030738 pc=0x40337f0
runtime.goparkunlock(...)
	/usr/local/go/src/runtime/proc.go:310
runtime.runfinq()
	/usr/local/go/src/runtime/mfinal.go:175 +0xa3 fp=0xc0000307e0 sp=0xc000030758 pc=0x4017773
runtime.goexit()
	/usr/local/go/src/runtime/asm_amd64.s:1373 +0x1 fp=0xc0000307e8 sp=0xc0000307e0 pc=0x405da91
created by runtime.createfing
	/usr/local/go/src/runtime/mfinal.go:156 +0x61
exit status 2

[odeke-em]

Thank you for this report @wangzhione and welcome to the Go project!

I can reproduce this even for Go1.13.12, Go1.12.17, but for Go1.11.13 there are CGO errors.

Kindly paging @ianlancetaylor @cherrymui

[luchsh]

I tried to debug this problem, it crashed at method runtime.heapBitsSetType.
After digging into the assembly,

(lldb) di -f -m
libverify.so`runtime.heapBitsSetType:
....
    0x4327139 <+2361>: cmpl   $0x20, %edi
    0x432713c <+2364>: sbbl   %eax, %eax
    0x432713e <+2366>: sbbl   %edx, %edx
    0x4327140 <+2368>: movzbl (%r10), %ebx
    0x4327144 <+2372>: andl   $0x3, %ebx
    0x4327147 <+2375>: orl    $0x10, %ebx
->  0x432714a <+2378>: movzbl (%rsi), %r8d
    0x432714e <+2382>: movl   %edi, %ecx
    0x4327150 <+2384>: movl   $0x33, %r9d
    0x4327156 <+2390>: shll   %cl, %r9d
    0x4327159 <+2393>: andl   %eax, %r9d

It looks like the heapAreana.bitmap corresponding to this newly allocated memory p is NULL.

I could not find an efficient debugger on Catalina to further dig into this problem;
lldb cannot set breakpoints; dlv and gdb cannot display symbols; Pls let me know if you have a working debugger on Catalina.

Then I tried to add many print statements to the Go runtime and found:

• the initialization code of the shared library got executed.
• but the shared library code was trying to access runtime.mheap_ from the main executable's Go runtime.
  And it could not find any records in mheap_.arenas[0][*] corresponding the memory p allocated via the shared library's runtime.mheap_.

But I still do not know why the shared library was accessing the wrong runtime.mheap_.
I've tried to rewrite the executable and the shared library in C language, and the following scenarios all work well:

• C-calls-Go
• Go-calls-C
• C-calls-C

any thoughts?

[ianlancetaylor]

A shared library built with -buildmode=c-shared is intended to be used with a C program, not a Go program.

I don't know whether the Mach-O symbol visibility rules can support using -buildmode=c-shared with a Go program.

[networkimprov]

Emmanual @odeke-em found that Go 1.11 gave a CGO error, not a segfault.