cmd/compile: internal compiler error len larger than cap for OSLICEHEADER

[lmaltsis]

Go version

go version go1.27-devel_b5c2bd7e05 Mon Mar 2 18:43:01 2026 -0800 linux/amd64

Output of go env in your module/workspace:

$ /research/compilers/go env
AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE=''
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/home/user/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/user/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build3429397299=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/dev/null'
GOMODCACHE='/home/user/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/user/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/user/software/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/user/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/home/user/software/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.27-devel_b5c2bd7e05 Mon Mar 2 18:43:01 2026 -0800'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

go.dev/play link: https://go.dev/play/p/8hCTRC1ehCi?v=gotip

on stable

$ go build /tmp/bug.go
# command-line-arguments
/tmp/bug.go:9:16: internal compiler error: len larger than cap for OSLICEHEADER

Please file a bug report including a short program that triggers the error.
https://go.dev/issue/new

$ cat /tmp/bug.go
package main
import (
	"fmt"
)

func main() {
	i := 0
	output := make([]string, 8, i)
	fmt.Println(output)
}

$ go version
go version go1.25.7 linux/amd64

on trunk with stacktrace

$ go build /tmp/bug.go
# command-line-arguments
/tmp/bug.go:9:16: internal compiler error: len larger than cap for OSLICEHEADER

[stacktrace below]

$ go version
go version go1.27-devel_b5c2bd7e05 Mon Mar 2 18:43:01 2026 -0800 linux/amd64

What did you see happen?

goroutine 1 [running]:
runtime/debug.Stack()
        /home/user/software/go/src/runtime/debug/stack.go:26 +0x5e
cmd/compile/internal/base.FatalfAt({0xfc5038?, 0x0?}, {0xf97731, 0x24}, {0x0, 0x0, 0x0})
        /home/user/software/go/src/cmd/compile/internal/base/print.go:232 +0x18b
cmd/compile/internal/base.Fatalf(...)
        /home/user/software/go/src/cmd/compile/internal/base/print.go:197
cmd/compile/internal/typecheck.tcSliceHeader(0x10f06a768120)
        /home/user/software/go/src/cmd/compile/internal/typecheck/expr.go:838 +0x34a
cmd/compile/internal/typecheck.typecheck1({0xfd2e28?, 0x10f06a768120?}, 0x12)
        /home/user/software/go/src/cmd/compile/internal/typecheck/typecheck.go:373 +0x1e16
cmd/compile/internal/typecheck.typecheck({0xfd2e28, 0x10f06a768120}, 0x12)
        /home/user/software/go/src/cmd/compile/internal/typecheck/typecheck.go:179 +0x1ad
cmd/compile/internal/typecheck.assign({0xfd36c0, 0x10f06a7625f0}, {0x10f069d72c88, 0x1, 0x60d7e5?}, {0x10f069d72c78, 0x1, 0x2?})
        /home/user/software/go/src/cmd/compile/internal/typecheck/stmt.go:82 +0xa5
cmd/compile/internal/typecheck.tcAssign(...)
        /home/user/software/go/src/cmd/compile/internal/typecheck/stmt.go:36
cmd/compile/internal/typecheck.typecheck1({0xfd36c0?, 0x10f06a7625f0?}, 0x1)
        /home/user/software/go/src/cmd/compile/internal/typecheck/typecheck.go:509 +0x305
cmd/compile/internal/typecheck.typecheck({0xfd36c0, 0x10f06a7625f0}, 0x1)
        /home/user/software/go/src/cmd/compile/internal/typecheck/typecheck.go:179 +0x1ad
cmd/compile/internal/typecheck.Stmt(...)
        /home/user/software/go/src/cmd/compile/internal/typecheck/typecheck.go:20
cmd/compile/internal/walk.appendWalkStmt(0x10f069d73770, {0xfd36c0, 0x10f06a7625f0})
        /home/user/software/go/src/cmd/compile/internal/walk/walk.go:263 +0x46
cmd/compile/internal/walk.walkMakeSlice(0x10f069d863c0, 0x10f069d73770)
        /home/user/software/go/src/cmd/compile/internal/walk/builtin.go:545 +0x16a9
cmd/compile/internal/walk.walkExpr1({0xfd4728, 0x10f069d863c0}, 0x10f069d73770)
        /home/user/software/go/src/cmd/compile/internal/walk/expr.go:312 +0x89e
cmd/compile/internal/walk.walkExpr({0xfd4728, 0x10f069d863c0}, 0x10f069d73770)
        /home/user/software/go/src/cmd/compile/internal/walk/expr.go:60 +0x328
cmd/compile/internal/walk.walkAssign(0x10f069d73770, {0xfd36c0, 0x10f069d77a90})
        /home/user/software/go/src/cmd/compile/internal/walk/assign.go:73 +0xd2f
cmd/compile/internal/walk.walkExpr1({0xfd36c0, 0x10f069d77a90}, 0x10f069d73770)
        /home/user/software/go/src/cmd/compile/internal/walk/expr.go:204 +0x408
cmd/compile/internal/walk.walkExpr({0xfd36c0, 0x10f069d77a90}, 0x10f069d73770)
        /home/user/software/go/src/cmd/compile/internal/walk/expr.go:60 +0x328
cmd/compile/internal/walk.walkStmt({0xfd36c0, 0x10f069d77a90})
        /home/user/software/go/src/cmd/compile/internal/walk/stmt.go:60 +0x51a
cmd/compile/internal/walk.walkStmtList(...)
        /home/user/software/go/src/cmd/compile/internal/walk/stmt.go:176
cmd/compile/internal/walk.Walk(0x10f069cf1180)
        /home/user/software/go/src/cmd/compile/internal/walk/walk.go:43 +0x27b
cmd/compile/internal/gc.prepareFunc(0x10f069cf1180)
        /home/user/software/go/src/cmd/compile/internal/gc/compile.go:123 +0x105
cmd/compile/internal/gc.enqueueFunc(0x10f069cf1180, 0x10f069d73bb0)
        /home/user/software/go/src/cmd/compile/internal/gc/compile.go:85 +0x351
cmd/compile/internal/gc.Main(0x18fdb50)
        /home/user/software/go/src/cmd/compile/internal/gc/main.go:333 +0x152b
main.main()
        /home/user/software/go/src/cmd/compile/main.go:57 +0xf9

What did you expect to see?

Same behavior as https://go.dev/play/p/63hF9Fibhsy?v=gotip

$ cat /tmp/correct.go
package main
import (
        "fmt"
)

func main() {
        output := make([]string, 8, 0)
        fmt.Println(output)
}

$ go build /tmp/correct.go
./prog.go:8:27: invalid argument: length and capacity swapped

[gabyhelp]

Related Issues

• cmd/compile: internal compiler error: not lowered: v108, Zero SSA PTR SSA #59174 (closed)
• cmd/compile: ICE when using unsafe.Sizeof on generic type #77382 (closed)
• cmd/compile: internal compiler error: assigning to non-1-length array #19671 (closed)
• cmd/compile: runtime error: makeslice: len out of range #20529 (closed)
• cmd/compile: "bad ptr to array in slice" in SSA slice handling #71252
• cmd/compile: bad export data for composite literal with elided type #15572 (closed)
• cmd/compile: internal compiler error: unhandled OCONV ARRAY -> UINT8 #52020 (closed)
• cmd/compile: internal compiler error: panic during prove #68816 (closed)
• cmd/compile: internal compiler error: TempAt called with nil type #49240 (closed)
• cmd/compile: internal compiler error in unaligned pointer write #61187 (closed)

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

[gopherbot]

Change https://go.dev/cl/751040 mentions this issue: cmd/compile/internal/typecheck: simplify tcSliceHeader

[cuonglm]

@gopherbot Please backport this to go1.25 and go1.26 branch.

This causes an ICE when compiling certain programs with non-constant argument to make.

[gopherbot]

Backport issue(s) opened: #77921 (for 1.25), #77922 (for 1.26).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://go.dev/wiki/MinorReleases.

[gopherbot]

Change https://go.dev/cl/751380 mentions this issue: cmd/compile: remove left over constant checking