cmd/go: Tests failing when init accesses a byte slice larger than 65536 with go test -cover

[maxkidd]

Go version

go version go1.24.2 windows/amd64

Output of go env in your module/workspace:

set AR=ar
set CC=gcc
set CGO_CFLAGS=-O2 -g
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-O2 -g
set CGO_ENABLED=0
set CGO_FFLAGS=-O2 -g
set CGO_LDFLAGS=-O2 -g
set CXX=g++
set GCCGO=gccgo
set GO111MODULE=
set GOAMD64=v1
set GOARCH=amd64
set GOAUTH=netrc
set GOBIN=
set GOCACHE=C:\Users\maxki\AppData\Local\go-build
set GOCACHEPROG=
set GODEBUG=
set GOENV=C:\Users\maxki\AppData\Roaming\go\env
set GOEXE=.exe
set GOEXPERIMENT=
set GOFIPS140=off
set GOFLAGS=
set GOGCCFLAGS=-m64 -fno-caret-diagnostics -Qunused-arguments -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=C:\Users\maxki\AppData\Local\Temp\go-build2150697774=/tmp/go-build -gno-record-gcc-switches
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOINSECURE=
set GOMOD=NUL
set GOMODCACHE=C:\Users\maxki\go\pkg\mod
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\maxki\go
set GOPRIVATE=
set GOPROXY=https://proxy.golang.org,direct
set GOROOT=C:\Program Files\Go
set GOSUMDB=sum.golang.org
set GOTELEMETRY=local
set GOTELEMETRYDIR=C:\Users\maxki\AppData\Roaming\go\telemetry
set GOTMPDIR=
set GOTOOLCHAIN=auto
set GOTOOLDIR=C:\Program Files\Go\pkg\tool\windows_amd64
set GOVCS=
set GOVERSION=go1.24.2
set GOWORK=
set PKG_CONFIG=pkg-config

What did you do?

Write a file with a global byte slice larger than 1<16. Access it in the init() func. Also add a test file (can be empty). call 'go test -cover'

package testbed

var (
	indexes [65537]byte
)

func init() {
	indexes[0] = 0x00
}

What did you see happen?

PS C:\Users\maxki\go\src\nbio\testbed> go test -cover
testing: warning: no tests to run
PASS
panic: runtime error: slice bounds out of range [:16777222] with capacity 7

goroutine 1 [running]:
internal/coverage/cfile.(*emitState).VisitFuncs(0xc00006a8c0, 0xc000008330)
        C:/Program Files/Go/src/internal/coverage/cfile/emit.go:478 +0xdb0
internal/coverage/encodecounter.(*CoverageDataWriter).writeCounters(0xc00009a0f0, {0x109ddc0, 0xc00006a8c0}, 0xc00005a700)
        C:/Program Files/Go/src/internal/coverage/encodecounter/encode.go:278 +0x10b
internal/coverage/encodecounter.(*CoverageDataWriter).AppendSegment(0xc00009a0f0, 0xc00001ef30, {0x109ddc0, 0xc00006a8c0})
        C:/Program Files/Go/src/internal/coverage/encodecounter/encode.go:178 +0x4b2
internal/coverage/encodecounter.(*CoverageDataWriter).Write(0xc00009a0f0, {0xca, 0xc4, 0x3b, 0x46, 0xbb, 0xcb, 0xf6, 0x57, 0xfa, ...}, ...)
        C:/Program Files/Go/src/internal/coverage/encodecounter/encode.go:70 +0x54
internal/coverage/cfile.(*emitState).emitCounterDataFile(0xc00006a8c0, {0xca, 0xc4, 0x3b, 0x46, 0xbb, 0xcb, 0xf6, 0x57, 0xfa, ...}, ...)
        C:/Program Files/Go/src/internal/coverage/cfile/emit.go:566 +0x4e
internal/coverage/cfile.emitCounterDataToDirectory({0xc0000180d1, 0x44})
        C:/Program Files/Go/src/internal/coverage/cfile/emit.go:318 +0x165
internal/coverage/cfile.ProcessCoverTestDir({0xc0000180d1, 0x44}, {0x0, 0x0}, {0x1057f03?, 0x0?}, {0x0, 0x0}, {0x109dcb8, 0xc000056070}, ...)
        C:/Program Files/Go/src/internal/coverage/cfile/testsupport.go:46 +0x17e
testing/internal/testdeps.coverTearDown({0x0, 0x0}, {0xc0000180d1?, 0x0?})
        C:/Program Files/Go/src/testing/internal/testdeps/deps.go:236 +0x159
testing.coverReport2()
        C:/Program Files/Go/src/testing/newcover.go:43 +0x3a
testing.coverReport(...)
        C:/Program Files/Go/src/testing/cover.go:86
testing.(*M).writeProfiles(0xc00006a6e0)
        C:/Program Files/Go/src/testing/testing.go:2433 +0x72b
testing.(*M).after.func1()
        C:/Program Files/Go/src/testing/testing.go:2367 +0x17
sync.(*Once).doSlow(0xc00000c3c0?, 0x5?)
        C:/Program Files/Go/src/sync/once.go:78 +0xab
sync.(*Once).Do(...)
        C:/Program Files/Go/src/sync/once.go:69
testing.(*M).after(0xc00006a6e0)
        C:/Program Files/Go/src/testing/testing.go:2366 +0x3b
testing.(*M).Run(0xc00006a6e0)
        C:/Program Files/Go/src/testing/testing.go:2185 +0xb8b
main.main()
        _testmain.go:53 +0x9b
exit status 2

What did you expect to see?

Pass with a coverage percent

[gabyhelp]

Related Issues

• cmd/go: TestScript/cover_pkgall_imports failures #69300
• runtime/coverage: `slice bounds out of range` in `(*emitState).VisitFuncs` #58936
• cmd/go: Stack overflow on running: go test -race with -coverpkg=all #23694 (closed)
• internal/coverage: runtime.(*wbBuf).putFast SEGV in cover-related cmd/go tests on 386 #56044 (closed)
• cmd/go: TestScript/cover_atomic_pkgall failures #70146
• cmd/go: go 1.22.0: go test throws errors when processing folders not listed in coverpkg argument #65653 (closed)
• cmd/go: data race when running test with coverprofile #56006 (closed)
• coverage: [no statements] #42118 (closed)
• cmd/link: Oversize object file (example uses generics) causes confusing "slice bounds out of range" panic #66357
• cmd/compile: crash in make running generic code [1.18 backport] #52311 (closed)

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[JunyangShao]

@matloob