go/compile: Panics involving defer statements do not consistently display line with defer in stack traces

[varungandhi-src]

Go version

go version go1.23.0 darwin/arm64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='arm64'
GOBIN='/Users/varun/.local/share/mise/installs/go/1.23.0/bin'
GOCACHE='/Users/varun/Library/Caches/go-build'
GOENV='/Users/varun/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/varun/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/varun/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/Users/varun/.local/share/mise/installs/go/1.23.0'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/Users/varun/.local/share/mise/installs/go/1.23.0/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.23.0'
GODEBUG=''
GOTELEMETRY='local'
GOTELEMETRYDIR='/Users/varun/Library/Application Support/go/telemetry'
GCCGO='gccgo'
GOARM64='v8.0'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/tr/gylnxkts3bn0gyhhlrv8z9_m0000gn/T/go-build4046955043=/tmp/go-build -gno-record-gcc-switches -fno-common'

What did you do?

When you have defer func() { /* code */ () and there is a nil pointer dereference in the body of func, then the stack trace (correctly) shows the line inside the func() where the nil pointer dereference happened. (Example: https://go.dev/play/p/qjGg11jBLwD)

func main() {
	s := struct{ f func() }{}
	defer func() {
		s.f()
	}()
}

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x4665ae]

goroutine 1 [running]:
main.main.func1()
	/tmp/sandbox2783684081/prog.go:8 +0xe
main.main()
	/tmp/sandbox2783684081/prog.go:10 +0x48

However, if you don't have a func() then the defer line is not shown in the panic (Example: https://go.dev/play/p/1tvIBFvpdss)

import "fmt"

func main() {
	s := struct{ f func() }{}
	defer s.f()
	fmt.Printf("Hello World\n!")
}

main.main()
	/tmp/sandbox3104930147/prog.go:11 +0x5a

This can make debugging quite confusing, as the final line in the stack trace might actually not have any code at all, or it might have some code which can never have a nil pointer exception.

What did you see happen?

Missing entry in the stack trace. See the section above.

What did you expect to see?

There should be an extra entry in the stack trace pointing to the appropriate line in the defer statement where the nil pointer dereference actually happened.

Aside

This issue is based on a confusing stack trace that my colleague @antonsviridov-src debugged earlier today.

[gabyhelp]

Related Issues and Documentation

• runtime: panic reported on wrong line on deferred statements #41180 (closed)
• `bad defer entry in panic` with panic in defer #61059 (closed)
• runtime: confusing stack trace in case of deferring <nil> function #15466 (closed)
• runtime: stack traces do not indicate the caller for deferred calls #46757
• cmd/compile: misleading panic on deferred func #29797
• cmd/compile: "Open defer" of method call miscompiled at tip #45062 (closed)
• runtime: missing deferreturn on linux/ppc64le #39049 (closed)
• runtime: arm64 bt in Delve get endless main.main after nil pointer dereference #63862 (closed)
• runtime: stacktrace for deferred code which panics is too subtle for me #45794
• runtime/trace: segfault in runtime.fpTracebackPCs during deferred call after recovering from panic #61766 (closed)

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[varungandhi-src]

Closing this as a duplicate of #29797