cmd/compile: invalid memory address or nil pointer dereference in gc.convlit1

[zikaeroh]

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

Installing tip at 3bea90d (can't use gotip version because it failed to build).

Does this issue reproduce with the latest release?

N/A

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/jake/.cache/go-build"
GOENV="/home/jake/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/jake/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/lib/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
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 -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build095132304=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Ran gotip download to build the latest tip.

What did you expect to see?

A successful build.

What did you see instead?

$ gotip download
Updating the go development tree...
remote: Counting objects: 58, done
remote: Finding sources: 100% (38/38)
remote: Total 38 (delta 9), reused 27 (delta 9)
Unpacking objects: 100% (38/38), done.
From https://go.googlesource.com/go
   498eaee4..3bea90d8  master     -> origin/master
Previous HEAD position was 498eaee4 cmd/internal/obj/x86: mark 2-instruction TLS access nonpreemptible
HEAD is now at 3bea90d8 cmd/go: allow a fork with path […]/vN to replace gopkg.in/[…].vN
Building Go cmd/dist using /usr/lib/go. (go1.13.4 linux/amd64)
Building Go toolchain1 using /usr/lib/go.
Building Go bootstrap cmd/go (go_bootstrap) using Go toolchain1.
Building Go toolchain2 using go_bootstrap and Go toolchain1.
Building Go toolchain3 using go_bootstrap and Go toolchain2.
Building packages and commands for linux/amd64.
# crypto/des
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x54 pc=0xc0d48b]

goroutine 1 [running]:
cmd/compile/internal/gc.convlit1(0xc0004bda80, 0xc000100a80, 0xc0003bfa00, 0xc0003bf780, 0xc0004dff01)
	/home/jake/sdk/gotip/src/cmd/compile/internal/gc/const.go:246 +0xfb
cmd/compile/internal/gc.assignconvfn(0xc0004bda80, 0xc000100a80, 0xc0003bf780, 0xc0004dff80)
	/home/jake/sdk/gotip/src/cmd/compile/internal/gc/subr.go:805 +0x9e
cmd/compile/internal/gc.assignconv(0xc0004bda80, 0xc000100a80, 0xe4f344, 0xd, 0xc0004dff80)
	/home/jake/sdk/gotip/src/cmd/compile/internal/gc/subr.go:792 +0x70
cmd/compile/internal/gc.typecheckarraylit(0xc000100a80, 0x10, 0xc0004bd380, 0x10, 0x10, 0xe4f344, 0xd, 0x10)
	/home/jake/sdk/gotip/src/cmd/compile/internal/gc/typecheck.go:2999 +0x16a
cmd/compile/internal/gc.typecheckcomplit(0xc0004bd300, 0x0)
	/home/jake/sdk/gotip/src/cmd/compile/internal/gc/typecheck.go:2807 +0x1cb8
cmd/compile/internal/gc.typecheck1(0xc0004bd300, 0x2, 0x0)
	/home/jake/sdk/gotip/src/cmd/compile/internal/gc/typecheck.go:860 +0x44f9
cmd/compile/internal/gc.typecheck(0xc0004bd300, 0x2, 0x0)
	/home/jake/sdk/gotip/src/cmd/compile/internal/gc/typecheck.go:300 +0x704
cmd/compile/internal/gc.typecheckarraylit(0xc0004c3ec0, 0x4, 0xc0004b8e00, 0x4, 0x4, 0xe4f344, 0xd, 0x4)
	/home/jake/sdk/gotip/src/cmd/compile/internal/gc/typecheck.go:2998 +0x135
cmd/compile/internal/gc.typecheckcomplit(0xc0004bc080, 0x0)
	/home/jake/sdk/gotip/src/cmd/compile/internal/gc/typecheck.go:2807 +0x1cb8
cmd/compile/internal/gc.typecheck1(0xc0004bc080, 0x2, 0x0)
	/home/jake/sdk/gotip/src/cmd/compile/internal/gc/typecheck.go:860 +0x44f9
cmd/compile/internal/gc.typecheck(0xc0004bc080, 0x2, 0x0)
	/home/jake/sdk/gotip/src/cmd/compile/internal/gc/typecheck.go:300 +0x704
cmd/compile/internal/gc.typecheckarraylit(0xc0004c3f20, 0x8, 0xc000468500, 0x8, 0x8, 0xe4f344, 0xd, 0x30)
	/home/jake/sdk/gotip/src/cmd/compile/internal/gc/typecheck.go:2998 +0x135
cmd/compile/internal/gc.typecheckcomplit(0xc0004a1d00, 0x0)
	/home/jake/sdk/gotip/src/cmd/compile/internal/gc/typecheck.go:2807 +0x1cb8
cmd/compile/internal/gc.typecheck1(0xc0004a1d00, 0x12, 0x0)
	/home/jake/sdk/gotip/src/cmd/compile/internal/gc/typecheck.go:860 +0x44f9
cmd/compile/internal/gc.typecheck(0xc0004a1d00, 0x12, 0x0)
	/home/jake/sdk/gotip/src/cmd/compile/internal/gc/typecheck.go:300 +0x704
cmd/compile/internal/gc.typecheckas(0xc0004c0500)
	/home/jake/sdk/gotip/src/cmd/compile/internal/gc/typecheck.go:3172 +0xa1
cmd/compile/internal/gc.typecheck1(0xc0004c0500, 0x1, 0x0)
	/home/jake/sdk/gotip/src/cmd/compile/internal/gc/typecheck.go:1900 +0x2fcc
cmd/compile/internal/gc.typecheck(0xc0004c0500, 0x1, 0x0)
	/home/jake/sdk/gotip/src/cmd/compile/internal/gc/typecheck.go:300 +0x704
cmd/compile/internal/gc.Main(0xe6ebd0)
	/home/jake/sdk/gotip/src/cmd/compile/internal/gc/main.go:580 +0x2a6c
main.main()
	/home/jake/sdk/gotip/src/cmd/compile/main.go:50 +0xac
go tool dist: FAILED: /home/jake/sdk/gotip/pkg/tool/linux_amd64/go_bootstrap install -gcflags=all= -ldflags=all= std cmd: exit status 2
gotip: failed to build go: exit status 2

Rerunning gotip download was successful, so I'm not sure how reproducible this is.

[andybons]

@randall77 @griesemer
@josharian @mdempsky @martisch

[mdempsky]

Is the failure reproducible or was it one time?

I suspect runtime memory corruption if it doesn't reproduce.

[zikaeroh]

As far as I can tell, it's a one-off or just really rare. I haven't seen it since, but I haven't rebuilt the toolchain all that many times today. (I get the corruption in #35326 way more often and consistently.)

[mdempsky]

Yeah, runtime memory corruption seems most likely to me then.

The nil pointer dereference happened here:

go/src/cmd/compile/internal/gc/const.go

Line 246 in 72f333a

if n.Type.Etype == TNIL {

But just a few lines earlier we have:

go/src/cmd/compile/internal/gc/const.go

Lines 230 to 233 in 72f333a

	if n == nil || n.Type == nil {
	// Allow sloppy callers.
	return n
	}

The only intermediate code that modifies n or n.Type is:

go/src/cmd/compile/internal/gc/const.go

Lines 239 to 243 in 72f333a

	if n.Op == OLITERAL {
	// Can't always set n.Type directly on OLITERAL nodes.
	// See discussion on CL 20813.
	n = n.rawcopy()
	}

but that just calls

go/src/cmd/compile/internal/gc/subr.go

Lines 387 to 390 in 72f333a

	func (n *Node) rawcopy() *Node {
	copy := *n
	return &copy
	}

which is plainly safe.

[aclements]

@zikaeroh, I assume this is on the same 5.3.x kernel as you reported in #35326? If so, this is almost certainly the same issue (though having more data points is useful).

[zikaeroh]

Yep, that's correct. I was just about to comment on your mega issue with a link here.

Feel free to close this in favor of #35777 once you've gotten whatever info you wanted.

[aclements]

Thanks. I've added this to the super-bug. Since this isn't reproducible, closing in favor of the super-bug.