Golang runtime: defer recover doesn't handle consistently

Go version

1.24.4

Output of go env in your module/workspace:

AR='ar'
CC='cc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='c++'
GCCGO='gccgo'
GO111MODULE=''
GOARCH='arm64'
GOARM64='v8.0'
GOAUTH='netrc'
GOBIN='$HOME/go/bin'
GOCACHE='$HOME/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='$HOME/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/tmp/go-build=/tmp/go-build -gno-record-gcc-switches -fno-common'
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMOD='$PROJECT_PATH/go.mod'
GOMODCACHE='$HOME/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='$HOME/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='$HOME/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.24.4'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

I tried two code snippets. The first one:

package main

import "fmt"

func main() {
    defer func() {
        recoverHelper()
    }()

    panic("oops")
}

func recoverHelper() {
    if r := recover(); r != nil {
        fmt.Println("Recovered:", r)
    }
}

The second snippet adds an argument to the anonymous function (which forces the compiler to generate a defer wrapper):

package main

import "fmt"

func main() {
    defer func(i int) {
        recoverHelper()
    }(1)

    panic("oops")
}

func recoverHelper() {
    if r := recover(); r != nil {
        fmt.Println("Recovered:", r)
    }
}

What did you see happen?

The first snippet panics, but the second one does not.

---

My suspicion is that the second snippet creates a defer wrapper and changes _panic.argp to point to the wrapper's stack frame itself. The anonymous function is inlined with a large budget (800), making the wrapper think it is calling recoverHelper directly. As a result, recoverHelper has the same argument pointer value as _panic.argp, so when gorecover is called, it successfully recovers.

What did you expect to see?

Both of them panic.

Comment From: zigo101

The second doesn't panic since Go toolchain 1.22.

Comment From: gabyhelp

Related Issues

• cmd/compile: incorrect recover behavior due to defer wrapper #73916
• builtin: recover returns nil in an anonymous function from an variable #56254 (closed)
• `defer recover()` does not recover from panic #53169 (closed)
• affected/package: builtin Inlining causes spec violation in recover() #54119 (closed)
• cmd/compile: yet another incorrect recover behavior due to defer a method wrapper #73920
• go/compile: Panics involving defer statements do not consistently display line with defer in stack traces #69761 (closed)
• builtin: can't "defer recover()" without an anonymous func #20768 (closed)
• `bad defer entry in panic` with panic in defer #61059 (closed)
• runtime: can't recover #50512 (closed)
• Documentation: deferring a recover directly is a no-op (spec) #25815 (closed)

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

Comment From: func25

Closed as duplicate of https://github.com/golang/go/issues/73916.