runtime: cgoCheckPointer fatal error: can't happen

[004helix]

Go version

go version go1.23.2 linux/amd64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/user/.cache/go-build'
GOENV='/home/user/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/user/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/user/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go1.23'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go1.23/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.23.2'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/user/.config/go/telemetry'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/home/user/git/vsis_bridge/src/bridge/go.mod'
GOWORK='/home/user/git/vsis_bridge/src/bridge/go.work'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build1230936848=/tmp/go-build -gno-record-gcc-switches'

What did you do?

main.go

package main

// void test(void *a) {}
import "C"
import "unsafe"

func errBufPtr(buf *[256]byte) unsafe.Pointer {
	return unsafe.Pointer(&buf[0])
}

func main() {
	buf := new([256]byte)

	// run ok
	C.test(errBufPtr(buf))

	// panic: fatal error: can't happen
	C.test(unsafe.Pointer(&buf[0]))
}

What did you see happen?

$ go run main.go

fatal error: can't happen

goroutine 1 gp=0xc0000061c0 m=0 mp=0x4fbe40 [running]:
runtime.throw({0x47efcd?, 0x4fbe40?})
        /usr/local/go1.23/src/runtime/panic.go:1067 +0x48 fp=0xc000080ea8 sp=0xc000080e78 pc=0x460048
runtime.cgoCheckPointer({0x4718a0, 0xc00010e200}, {0x470a20, 0xc00010e200})
        /usr/local/go1.23/src/runtime/cgocall.go:567 +0x185 fp=0xc000080ef0 sp=0xc000080ea8 pc=0x45d6a5
main.main.func2(0x4f9b20?)
        /home/user/tmp/main.go:18 +0x2e fp=0xc000080f28 sp=0xc000080ef0 pc=0x46aa6e
main.main()
        /home/user/tmp/main.go:18 +0x33 fp=0xc000080f50 sp=0xc000080f28 pc=0x46aa13
runtime.main()
        /usr/local/go1.23/src/runtime/proc.go:272 +0x28b fp=0xc000080fe0 sp=0xc000080f50 pc=0x43370b
runtime.goexit({})
        /usr/local/go1.23/src/runtime/asm_amd64.s:1700 +0x1 fp=0xc000080fe8 sp=0xc000080fe0 pc=0x4664a1

goroutine 2 gp=0xc000006c40 m=nil [force gc (idle)]:
runtime.gopark(0x0?, 0x0?, 0x0?, 0x0?, 0x0?)
        /usr/local/go1.23/src/runtime/proc.go:424 +0xce fp=0xc000068fa8 sp=0xc000068f88 pc=0x46012e
runtime.goparkunlock(...)
        /usr/local/go1.23/src/runtime/proc.go:430
runtime.forcegchelper()
        /usr/local/go1.23/src/runtime/proc.go:337 +0xb3 fp=0xc000068fe0 sp=0xc000068fa8 pc=0x433a53
runtime.goexit({})
        /usr/local/go1.23/src/runtime/asm_amd64.s:1700 +0x1 fp=0xc000068fe8 sp=0xc000068fe0 pc=0x4664a1
created by runtime.init.7 in goroutine 1
        /usr/local/go1.23/src/runtime/proc.go:325 +0x1a

goroutine 3 gp=0xc000007180 m=nil [GC sweep wait]:
runtime.gopark(0x0?, 0x0?, 0x0?, 0x0?, 0x0?)
        /usr/local/go1.23/src/runtime/proc.go:424 +0xce fp=0xc000069780 sp=0xc000069760 pc=0x46012e
runtime.goparkunlock(...)
        /usr/local/go1.23/src/runtime/proc.go:430
runtime.bgsweep(0xc00001e200)
        /usr/local/go1.23/src/runtime/mgcsweep.go:277 +0x94 fp=0xc0000697c8 sp=0xc000069780 pc=0x41fa34
runtime.gcenable.gowrap1()
        /usr/local/go1.23/src/runtime/mgc.go:203 +0x25 fp=0xc0000697e0 sp=0xc0000697c8 pc=0x4143c5
runtime.goexit({})
        /usr/local/go1.23/src/runtime/asm_amd64.s:1700 +0x1 fp=0xc0000697e8 sp=0xc0000697e0 pc=0x4664a1
created by runtime.gcenable in goroutine 1
        /usr/local/go1.23/src/runtime/mgc.go:203 +0x66

goroutine 4 gp=0xc000007340 m=nil [GC scavenge wait]:
runtime.gopark(0xc00001e200?, 0x49bc20?, 0x1?, 0x0?, 0xc000007340?)
        /usr/local/go1.23/src/runtime/proc.go:424 +0xce fp=0xc000069f78 sp=0xc000069f58 pc=0x46012e
runtime.goparkunlock(...)
        /usr/local/go1.23/src/runtime/proc.go:430
runtime.(*scavengerState).park(0x4fb0a0)
        /usr/local/go1.23/src/runtime/mgcscavenge.go:425 +0x49 fp=0xc000069fa8 sp=0xc000069f78 pc=0x41d469
runtime.bgscavenge(0xc00001e200)
        /usr/local/go1.23/src/runtime/mgcscavenge.go:653 +0x3c fp=0xc000069fc8 sp=0xc000069fa8 pc=0x41d9dc
runtime.gcenable.gowrap2()
        /usr/local/go1.23/src/runtime/mgc.go:204 +0x25 fp=0xc000069fe0 sp=0xc000069fc8 pc=0x414365
runtime.goexit({})
        /usr/local/go1.23/src/runtime/asm_amd64.s:1700 +0x1 fp=0xc000069fe8 sp=0xc000069fe0 pc=0x4664a1
created by runtime.gcenable in goroutine 1
        /usr/local/go1.23/src/runtime/mgc.go:204 +0xa5
exit status 2

What did you expect to see?

run without error

[gabyhelp]

Related Issues and Documentation

• go build use -asan it panic. #69225 (closed)
• runtime: write of Go pointer 0xc0000b2330 to non-Go memory 0x7f0f9772f080 #28458 (closed)
• runtime: getArgInfo nil dereference #17471 (closed)
• cmd/compile: unsafe.{SliceData,StringData} possible memory corruption in escape analysis #57823 (closed)
• runtime,misc/cgo/test: timeout in TestSetgidStress on linux-amd64 #54787 (closed)
• runtime: runtime.Breakpoint() generates illegal instruction on windows/arm64 #53837 (closed)
• runtime: spurious SIGSEGV in systemstack() #68632
• runtime: crash when trying go run or go build #37638 (closed)
• runtime: panic issues with go get #16634 (closed)
• runtime: runtime crashes, reproducer same as #20427 #36371 (closed)

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[randall77]

I can reproduce at tip on Darwin.

@ianlancetaylor The runtime is not expecting a *[256]byte typed second argument to cgoCheckPointer.

[ianlancetaylor]

Thanks for providing a simple standalone test case.

Sent https://go.dev/cl/621576 to fix this.

[gopherbot]

Change https://go.dev/cl/621576 mentions this issue: runtime: support cgo index into pointer-to-array