go: runtime: missing deferreturn on linux/ppc64le

What version of Go are you using (go version)?

$ go version
go version go1.14.2 linux/ppc64le

Does this issue reproduce with the latest release?

Yes, the same issue exists on tip.

This is a regression between Go 1.13 and Go 1.14, presumably either due to the introduction of open coded defers, or due to a bug that is now being triggered.

What operating system and processor architecture are you using (go env)?

$ go env
GO111MODULE=""
GOARCH="ppc64le"
GOBIN=""
GOCACHE="/home/jsing/.cache/go-build"
GOENV="/home/jsing/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="ppc64le"
GOHOSTOS="linux"
GOINSECURE=""
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/jsing/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/jsing/src/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/jsing/src/go/pkg/tool/linux_ppc64le"
GCCGO="gccgo"
GOPPC64="power8"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build042050806=/tmp/go-build -gno-record-gcc-switches"

What did you do?

This was initially observed when trying to run tests in a large code base on linux/ppc64le. In order to reproduce the issue, a panic() and defer() needs to be run at a high PC - I’ve written a Go program (https://play.golang.org/p/CmKwSyteWhX) that produces a Go program that triggers this issue.

Save https://play.golang.org/p/CmKwSyteWhX as gen.go then run:

$ go run gen.go && go run crash/main.go

What did you expect to see?

$ go run gen.go && go run crash/main.go
panic: blah

goroutine 1 [running]:
main.f2()
        /home/jsing/tmp/crash/crash/main.go:20 +0x7c
main.f1()
        /home/jsing/tmp/crash/crash/main.go:16 +0x3c
main.main()
        /home/jsing/tmp/crash/crash/main.go:27 +0x24
exit status 2

What did you see instead?

$ go run gen.go && go run crash/main.go
fatal error: missing deferreturn
                                                                                      
runtime stack:           
runtime.throw(0x3ddde3d, 0x13)                                                                                                                                               
        /home/jsing/src/go/src/runtime/panic.go:1116 +0x5c   
runtime.addOneOpenDeferFrame.func1.1(0x3fffd6114a10, 0x0, 0x4260c00)
        /home/jsing/src/go/src/runtime/panic.go:753 +0x258
runtime.gentraceback(0x3dbf7ec, 0xc000084ed0, 0x0, 0xc000000180, 0x0, 0x0, 0x7fffffff, 0x3fffd6114ae0, 0x0, 0x0, ...)
        /home/jsing/src/go/src/runtime/traceback.go:334 +0xea0                                                                                                               
runtime.addOneOpenDeferFrame.func1()                                                  
        /home/jsing/src/go/src/runtime/panic.go:721 +0x8c
runtime.systemstack(0x0)
        /home/jsing/src/go/src/runtime/asm_ppc64x.s:269 +0x94
runtime.mstart()
        /home/jsing/src/go/src/runtime/proc.go:1041

goroutine 1 [running]:                                                                
runtime.systemstack_switch()                                                          
        /home/jsing/src/go/src/runtime/asm_ppc64x.s:216 +0x10 fp=0xc000084db0 sp=0xc000084d90 pc=0x625b0
runtime.addOneOpenDeferFrame(0xc000000180, 0x3dbf7ec, 0xc000084ed0)
        /home/jsing/src/go/src/runtime/panic.go:720 +0x7c fp=0xc000084e00 sp=0xc000084db0 pc=0x3886c
panic(0x3dc9680, 0x3e0d2c0)                                                           
        /home/jsing/src/go/src/runtime/panic.go:929 +0xdc fp=0xc000084ed0 sp=0xc000084e00 pc=0x38eac
main.f2()
        /home/jsing/tmp/crash/crash/main.go:20 +0x7c fp=0xc000084f00 sp=0xc000084ed0 pc=0x3dbf7ec


main.f1()                             
        /home/jsing/tmp/crash/crash/main.go:16 +0x3c fp=0xc000084f30 sp=0xc000084f00 pc=0x3dbf72c
main.main()
        /home/jsing/tmp/crash/crash/main.go:27 +0x24 fp=0xc000084f50 sp=0xc000084f30 pc=0x3dbf834
runtime.main()   
        /home/jsing/src/go/src/runtime/proc.go:203 +0x248 fp=0xc000084fc0 sp=0xc000084f50 pc=0x3bcd8
runtime.goexit()
        /home/jsing/src/go/src/runtime/asm_ppc64x.s:884 +0x4 fp=0xc000084fc0 sp=0xc000084fc0 pc=0x64b64
exit status 2            

Changing n from 4149 to 4148 in gen.go will reduce the number of instructions prior to the defer() and results in the test succeeding.