weak: Make panics on pointers to objects not allocated in heap

[grudzinski]

Go version

1.24

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='on'
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/home/roman/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/roman/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build3567574948=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/home/roman/go/src/github.com/grudzinski/tests/go.mod'
GOMODCACHE='/home/roman/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/roman/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/roman/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.24.0'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

package main

import (
	"weak"
)

func main() {
	type nothing [0]int // or struct{}
	p := new(nothing) // special case, points to an addr stub allocated in BSS
	weak.Make[nothing](p)
}

Another case

package main

import (
	"weak"
)

var n int // allocated in BSS
var np = &n 

func main() {
	weak.Make[int](np)
}

What did you see happen?

fatal error: getWeakHandle on invalid pointer

goroutine 1 gp=0xc000002380 m=0 mp=0x4f7d60 [running]:
runtime.throw({0x47fea8?, 0xc000034008?})
	/usr/local/go/src/runtime/panic.go:1096 +0x48 fp=0xc000062668 sp=0xc000062638 pc=0x460e08
runtime.getWeakHandle(0x516970)
	/usr/local/go/src/runtime/mheap.go:2269 +0x113 fp=0xc0000626b0 sp=0xc000062668 pc=0x425e73
runtime.getOrAddWeakHandle(0x516970)
	/usr/local/go/src/runtime/mheap.go:2201 +0x1c fp=0xc000062700 sp=0xc0000626b0 pc=0x425bbc
weak.runtime_registerWeakPointer(0x0?)
	/usr/local/go/src/runtime/mheap.go:2102 +0x13 fp=0xc000062718 sp=0xc000062700 pc=0x460833
weak.Make[...](0x516970?)
	/usr/local/go/src/weak/pointer.go:72 +0x5d fp=0xc000062730 sp=0xc000062718 pc=0x4692fd
main.main()
	/home/roman/go/src/github.com/grudzinski/tests/main.go:11 +0x25 fp=0xc000062750 sp=0xc000062730 pc=0x469285
runtime.main()
	/usr/local/go/src/runtime/proc.go:283 +0x28b fp=0xc0000627e0 sp=0xc000062750 pc=0x4344eb
runtime.goexit({})
	/usr/local/go/src/runtime/asm_amd64.s:1700 +0x1 fp=0xc0000627e8 sp=0xc0000627e0 pc=0x465f41

goroutine 2 gp=0xc0000028c0 m=nil [force gc (idle)]:
runtime.gopark(0x0?, 0x0?, 0x0?, 0x0?, 0x0?)
	/usr/local/go/src/runtime/proc.go:435 +0xce fp=0xc000062fa8 sp=0xc000062f88 pc=0x460eee
runtime.goparkunlock(...)
	/usr/local/go/src/runtime/proc.go:441
runtime.forcegchelper()
	/usr/local/go/src/runtime/proc.go:348 +0xb3 fp=0xc000062fe0 sp=0xc000062fa8 pc=0x434833
runtime.goexit({})
	/usr/local/go/src/runtime/asm_amd64.s:1700 +0x1 fp=0xc000062fe8 sp=0xc000062fe0 pc=0x465f41
created by runtime.init.7 in goroutine 1
	/usr/local/go/src/runtime/proc.go:336 +0x1a

goroutine 3 gp=0xc000002e00 m=nil [GC sweep wait]:
runtime.gopark(0x0?, 0x0?, 0x0?, 0x0?, 0x0?)
	/usr/local/go/src/runtime/proc.go:435 +0xce fp=0xc000063780 sp=0xc000063760 pc=0x460eee
runtime.goparkunlock(...)
	/usr/local/go/src/runtime/proc.go:441
runtime.bgsweep(0xc00007a000)
	/usr/local/go/src/runtime/mgcsweep.go:276 +0x94 fp=0xc0000637c8 sp=0xc000063780 pc=0x420734
runtime.gcenable.gowrap1()
	/usr/local/go/src/runtime/mgc.go:204 +0x25 fp=0xc0000637e0 sp=0xc0000637c8 pc=0x414e65
runtime.goexit({})
	/usr/local/go/src/runtime/asm_amd64.s:1700 +0x1 fp=0xc0000637e8 sp=0xc0000637e0 pc=0x465f41
created by runtime.gcenable in goroutine 1
	/usr/local/go/src/runtime/mgc.go:204 +0x66

goroutine 4 gp=0xc000002fc0 m=nil [GC scavenge wait]:
runtime.gopark(0xc00007a000?, 0x499910?, 0x1?, 0x0?, 0xc000002fc0?)
	/usr/local/go/src/runtime/proc.go:435 +0xce fp=0xc000063f78 sp=0xc000063f58 pc=0x460eee
runtime.goparkunlock(...)
	/usr/local/go/src/runtime/proc.go:441
runtime.(*scavengerState).park(0x4f6f80)
	/usr/local/go/src/runtime/mgcscavenge.go:425 +0x49 fp=0xc000063fa8 sp=0xc000063f78 pc=0x41e1e9
runtime.bgscavenge(0xc00007a000)
	/usr/local/go/src/runtime/mgcscavenge.go:653 +0x3c fp=0xc000063fc8 sp=0xc000063fa8 pc=0x41e75c
runtime.gcenable.gowrap2()
	/usr/local/go/src/runtime/mgc.go:205 +0x25 fp=0xc000063fe0 sp=0xc000063fc8 pc=0x414e05
runtime.goexit({})
	/usr/local/go/src/runtime/asm_amd64.s:1700 +0x1 fp=0xc000063fe8 sp=0xc000063fe0 pc=0x465f41
created by runtime.gcenable in goroutine 1
	/usr/local/go/src/runtime/mgc.go:205 +0xa5

What did you expect to see?

I expect no panics for this cases.

[mknyszek]

Indeed, I think we missed that we have to apply an exception for linker-allocated objects. SetFinalizer and AddCleanup do, so weak.Make should as well, but it's going to be a bit more complex for weak.Make since we still have to produce a weak.Pointer that compares equal.

I'll take a look and hopefully send a fix soon.

[gabyhelp]

Related Issues

• unique: panic for Make(struct{}{}) #69458 (closed)
• weak: Pointer.Value() panics for zero-valued receivers #71153 (closed)
• runtime: cgoCheckPointer fatal error: can't happen #70016 (closed)
• unique: `fatal error: getWeakHandle on invalid pointer` with `sbrk=1` #69729
• go build use -asan it panic. #69225 (closed)
• unique: Fatal errors (found bad pointer in Go heap, found pointer to free object) and memory corruption #69643 (closed)
• cmd/compile: unsafe.{SliceData,StringData} possible memory corruption in escape analysis #57823 (closed)
• runtime: go1.4 "fatal error: bad pointer" #12729 (closed)
• runtime: garbage collector found invalid heap pointer #21432 (closed)
• cmd/compile: value assigned to global fails to escape #29000 (closed)

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[gopherbot]

Change https://go.dev/cl/649460 mentions this issue: weak: accept linker-allocated objects to Make