runtime: netpollinit() incorrectly prints the error from `linux.Eventfd`

[AndersonQ]

Go version

go version go1.25.0 linux/amd64

Output of go env in your module/workspace:

AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE=''
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN='/home/ainsoph/devel/go/bin'
GOCACHE='/home/ainsoph/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/ainsoph/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build179359909=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/home/ainsoph/devel/github.com/elastic/00.0.wip/go-bug/go.mod'
GOMODCACHE='/home/ainsoph/devel/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/ainsoph/devel/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/ainsoph/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.25.0'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

I run a program with a seccomp policy which did not allow eventfd2. The program crashed with:

runtime: eventfd failed with 18446744073709551615
fatal error: runtime: eventfd failed

the following is a minimal version of what I run, with all allowed syscall, just missing eventfd2, which caused the panic:

package main

import (
	"log/slog"
	"os"

	"github.com/elastic/go-seccomp-bpf"
)

func main() {
	filter := seccomp.Filter{
		NoNewPrivs: true,
		Flag:       seccomp.FilterFlagTSync,
		Policy:     policy,
	}

	if err := seccomp.LoadFilter(filter); err != nil {
		slog.Warn("Syscall filter could not be installed", "error", err,
			"seccomp_filter", filter)
		return
	}

	path, err := os.Executable()
	if err != nil {
		panic(err)
	}

	os.Open(path)
}

var policy = seccomp.Policy{
	DefaultAction: seccomp.ActionErrno,
	Syscalls: []seccomp.SyscallGroup{
		{
			Action: seccomp.ActionAllow,
			Names: []string{
				"accept",
				"accept4",
				"access",
				"arch_prctl",
				"bind",
				"brk",
				"capget",
				"chmod",
				"chown",
				"clock_gettime",
				"clock_nanosleep",
				"clone",
				"clone3",
				"close",
				"connect",
				"dup",
				"dup2",
				"dup3",
				"epoll_create",
				"epoll_create1",
				"epoll_ctl",
				"epoll_pwait",
				"epoll_wait",
				"execve",
				"exit",
				"exit_group",
				"faccessat",
				"faccessat2",
				"fchdir",
				"fchmod",
				"fchmodat",
				"fchown",
				"fchownat",
				"fcntl",
				"fdatasync",
				"flock",
				"fstat",
				"fstatfs",
				"fsync",
				"ftruncate",
				"futex",
				"getcwd",
				"getdents",
				"getdents64",
				"geteuid",
				"getgid",
				"getpeername",
				"getpid",
				"getppid",
				"getrandom",
				"getrlimit",
				"getrusage",
				"getsockname",
				"getsockopt",
				"gettid",
				"gettimeofday",
				"getuid",
				"inotify_add_watch",
				"inotify_init1",
				"inotify_rm_watch",
				"ioctl",
				"kill",
				"listen",
				"lseek",
				"lstat",
				"madvise",
				"mincore",
				"mkdirat",
				"mmap",
				"mprotect",
				"munmap",
				"nanosleep",
				"newfstatat",
				"open",
				"openat",
				"pipe",
				"pipe2",
				"poll",
				"ppoll",
				"prctl",
				"pread64",
				"pselect6",
				"pwrite64",
				"read",
				"readlink",
				"readlinkat",
				"recvfrom",
				"recvmmsg",
				"recvmsg",
				"rename",
				"renameat",
				"rseq",
				"rt_sigaction",
				"rt_sigprocmask",
				"rt_sigreturn",
				"sched_getaffinity",
				"sched_yield",
				"sendfile",
				"sendmmsg",
				"sendmsg",
				"sendto",
				"set_robust_list",
				"setitimer",
				"setrlimit",
				"setsockopt",
				"shutdown",
				"sigaltstack",
				"socket",
				"splice",
				"stat",
				"statfs",
				"sysinfo",
				"tgkill",
				"time",
				"tkill",
				"uname",
				"unlink",
				"unlinkat",
				"wait4",
				"waitid",
				"write",
				"writev",
			},
		},
	},
}

What did you see happen?

run the program above

go run main.go 

it panics with:

runtime: eventfd failed with 18446744073709551615
fatal error: runtime: eventfd failed

goroutine 1 gp=0xc000002380 m=0 mp=0x6047e0 [running]:
runtime.throw({0x512dbf?, 0x200000003?})
	/usr/local/go/src/runtime/panic.go:1094 +0x48 fp=0xc000118c90 sp=0xc000118c60 pc=0x46fd08
runtime.netpollinit()
	/usr/local/go/src/runtime/netpoll_epoll.go:31 +0x14e fp=0xc000118d00 sp=0xc000118c90 pc=0x4395ce
runtime.netpollGenericInit()
	/usr/local/go/src/runtime/netpoll.go:224 +0x35 fp=0xc000118d18 sp=0xc000118d00 pc=0x438ed5
internal/poll.runtime_pollServerInit()
	/usr/local/go/src/runtime/netpoll.go:215 +0xf fp=0xc000118d28 sp=0xc000118d18 pc=0x46f24f
sync.(*Once).doSlow(0x0?, 0xc000118db0?)
	/usr/local/go/src/sync/once.go:78 +0xac fp=0xc000118d80 sp=0xc000118d28 pc=0x47ab2c
sync.(*Once).Do(...)
	/usr/local/go/src/sync/once.go:69
internal/poll.(*pollDesc).init(0xc00007e200, 0xc00007e1e0)
	/usr/local/go/src/internal/poll/fd_poll_runtime.go:39 +0x3c fp=0xc000118da0 sp=0xc000118d80 pc=0x4a2a1c
internal/poll.(*FD).Init(0xc00007e1e0, {0x50df51?, 0xc000018270?}, 0x80?)
	/usr/local/go/src/internal/poll/fd_unix.go:66 +0x45 fp=0xc000118dc0 sp=0xc000118da0 pc=0x4a2da5
os.newFile(0x3, {0xc000018270, 0x25}, 0x1, 0x0)
	/usr/local/go/src/os/file_unix.go:218 +0x15d fp=0xc000118e00 sp=0xc000118dc0 pc=0x4a43bd
os.openFileNolog({0xc000018270, 0x25}, 0x0, 0x0)
	/usr/local/go/src/os/file_unix.go:278 +0x17d fp=0xc000118e58 sp=0xc000118e00 pc=0x4a45dd
os.OpenFile({0xc000018270, 0x25}, 0x0, 0x0)
	/usr/local/go/src/os/file.go:412 +0x3e fp=0xc000118e88 sp=0xc000118e58 pc=0x4a3e7e
os.Open(...)
	/usr/local/go/src/os/file.go:390
main.main()
	/home/ainsoph/devel/github.com/elastic/00.0.wip/go-bug/main.go:28 +0x178 fp=0xc000118f50 sp=0xc000118e88 pc=0x4dd578
runtime.main()
	/usr/local/go/src/runtime/proc.go:285 +0x29d fp=0xc000118fe0 sp=0xc000118f50 pc=0x43ff5d
runtime.goexit({})
	/usr/local/go/src/runtime/asm_amd64.s:1693 +0x1 fp=0xc000118fe8 sp=0xc000118fe0 pc=0x476601

goroutine 2 gp=0xc0000028c0 m=nil [force gc (idle)]:
runtime.gopark(0x0?, 0x0?, 0x0?, 0x0?, 0x0?)
	/usr/local/go/src/runtime/proc.go:460 +0xce fp=0xc00006cfa8 sp=0xc00006cf88 pc=0x46fdee
runtime.goparkunlock(...)
	/usr/local/go/src/runtime/proc.go:466
runtime.forcegchelper()
	/usr/local/go/src/runtime/proc.go:373 +0xb3 fp=0xc00006cfe0 sp=0xc00006cfa8 pc=0x440293
runtime.goexit({})
	/usr/local/go/src/runtime/asm_amd64.s:1693 +0x1 fp=0xc00006cfe8 sp=0xc00006cfe0 pc=0x476601
created by runtime.init.7 in goroutine 1
	/usr/local/go/src/runtime/proc.go:361 +0x1a

goroutine 3 gp=0xc000002e00 m=nil [GC sweep wait]:
runtime.gopark(0x0?, 0x0?, 0x0?, 0x0?, 0x0?)
	/usr/local/go/src/runtime/proc.go:460 +0xce fp=0xc00006d780 sp=0xc00006d760 pc=0x46fdee
runtime.goparkunlock(...)
	/usr/local/go/src/runtime/proc.go:466
runtime.bgsweep(0xc000026080)
	/usr/local/go/src/runtime/mgcsweep.go:279 +0x94 fp=0xc00006d7c8 sp=0xc00006d780 pc=0x42b774
runtime.gcenable.gowrap1()
	/usr/local/go/src/runtime/mgc.go:212 +0x25 fp=0xc00006d7e0 sp=0xc00006d7c8 pc=0x41f9c5
runtime.goexit({})
	/usr/local/go/src/runtime/asm_amd64.s:1693 +0x1 fp=0xc00006d7e8 sp=0xc00006d7e0 pc=0x476601
created by runtime.gcenable in goroutine 1
	/usr/local/go/src/runtime/mgc.go:212 +0x66

goroutine 4 gp=0xc000002fc0 m=nil [GC scavenge wait]:
runtime.gopark(0xc000026080?, 0x53dfc8?, 0x1?, 0x0?, 0xc000002fc0?)
	/usr/local/go/src/runtime/proc.go:460 +0xce fp=0xc00006df78 sp=0xc00006df58 pc=0x46fdee
runtime.goparkunlock(...)
	/usr/local/go/src/runtime/proc.go:466
runtime.(*scavengerState).park(0x6038a0)
	/usr/local/go/src/runtime/mgcscavenge.go:425 +0x49 fp=0xc00006dfa8 sp=0xc00006df78 pc=0x429249
runtime.bgscavenge(0xc000026080)
	/usr/local/go/src/runtime/mgcscavenge.go:653 +0x3c fp=0xc00006dfc8 sp=0xc00006dfa8 pc=0x4297dc
runtime.gcenable.gowrap2()
	/usr/local/go/src/runtime/mgc.go:213 +0x25 fp=0xc00006dfe0 sp=0xc00006dfc8 pc=0x41f965
runtime.goexit({})
	/usr/local/go/src/runtime/asm_amd64.s:1693 +0x1 fp=0xc00006dfe8 sp=0xc00006dfe0 pc=0x476601
created by runtime.gcenable in goroutine 1
	/usr/local/go/src/runtime/mgc.go:213 +0xa5

goroutine 5 gp=0xc000003500 m=nil [GOMAXPROCS updater (idle)]:
runtime.gopark(0x0?, 0x0?, 0x0?, 0x0?, 0x0?)
	/usr/local/go/src/runtime/proc.go:460 +0xce fp=0xc00006e788 sp=0xc00006e768 pc=0x46fdee
runtime.goparkunlock(...)
	/usr/local/go/src/runtime/proc.go:466
runtime.updateMaxProcsGoroutine()
	/usr/local/go/src/runtime/proc.go:6706 +0xe7 fp=0xc00006e7e0 sp=0xc00006e788 pc=0x44e087
runtime.goexit({})
	/usr/local/go/src/runtime/asm_amd64.s:1693 +0x1 fp=0xc00006e7e8 sp=0xc00006e7e0 pc=0x476601
created by runtime.defaultGOMAXPROCSUpdateEnable in goroutine 1
	/usr/local/go/src/runtime/proc.go:6694 +0x37

goroutine 6 gp=0xc0000036c0 m=nil [finalizer wait]:
runtime.gopark(0x44f055?, 0x0?, 0x0?, 0x0?, 0x0?)
	/usr/local/go/src/runtime/proc.go:460 +0xce fp=0xc00006c620 sp=0xc00006c600 pc=0x46fdee
runtime.runFinalizers()
	/usr/local/go/src/runtime/mfinal.go:210 +0x107 fp=0xc00006c7e0 sp=0xc00006c620 pc=0x41e967
runtime.goexit({})
	/usr/local/go/src/runtime/asm_amd64.s:1693 +0x1 fp=0xc00006c7e8 sp=0xc00006c7e0 pc=0x476601
created by runtime.createfing in goroutine 1
	/usr/local/go/src/runtime/mfinal.go:172 +0x3d
exit status 2

What did you expect to see?

A panic like:

runtime: eventfd failed with 1
fatal error: runtime: eventfd failed

The printed value should be 1, not 18446744073709551615.
It seems to come from the fact errno, a uintptr is printed as -errno:
https://go.googlesource.com/go/+/refs/heads/master/src/runtime/netpoll_epoll.go#30

[gabyhelp]

Related Issues

• runtime: epollwait on fd 1 failed with 22 #68333 (closed)
• runtime: netpoll: eventfd ready for something unexpected #72900
• runtime: netpoll throw: break fd ready for something unexpected #67056 (closed)
• can't run go run projectname.go #31715 (closed)
• runtime: epollwait failed with ENOSYS on Windows Subsystem for Linux #25384 (closed)
• runtime: kevent on fd 0 failed with 9 fatal error: runtime: netpoll failed #48310 (closed)
• runtime: fatal error: checkdead: runnable g #63761
• runtime: fatal error: checkdead: runnable g #40368 (closed)
• cmd/go: "fatal error: concurrent map writes" during go get #35317 (closed)
• runtime: SIGBUS occurred during slice append #29208 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[mrkfrmn]

cc @golang/runtime

[gopherbot]

Change https://go.dev/cl/701796 mentions this issue: runtime: don't negate eventfd errno