mirror of
https://github.com/golang/go
synced 2024-11-06 00:26:11 -07:00
2d3216f4a8
The offset of an embedded field s.X must be relative to s and not to the implicit s.Field of which X is a direct field. Moreover, no indirections may happen on the path. Fixes #4909. R=nigeltao, ality, daniel.morsing, iant, gri, r CC=golang-dev https://golang.org/cl/8287043
81 lines
1.3 KiB
Go
81 lines
1.3 KiB
Go
// errorcheckoutput
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package main
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import "fmt"
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// We are going to define 256 types T(n),
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// such that T(n) embeds T(2n) and *T(2n+1).
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func main() {
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fmt.Printf("// errorcheck\n\n")
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fmt.Printf("package p\n\n")
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fmt.Println(`import "unsafe"`)
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// Dump types.
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for n := 1; n < 256; n++ {
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writeStruct(n)
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}
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// Dump leaves
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for n := 256; n < 512; n++ {
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fmt.Printf("type T%d int\n", n)
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}
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fmt.Printf("var t T1\n")
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fmt.Printf("var p *T1\n")
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// Simple selectors
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for n := 2; n < 256; n++ {
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writeDot(n)
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}
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// Double selectors
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for n := 128; n < 256; n++ {
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writeDot(n/16, n)
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}
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// Triple selectors
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for n := 128; n < 256; n++ {
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writeDot(n/64, n/8, n)
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}
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}
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const structTpl = `
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type T%d struct {
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A%d int
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T%d
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*T%d
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}
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`
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func writeStruct(n int) {
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fmt.Printf(structTpl, n, n, 2*n, 2*n+1)
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}
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func writeDot(ns ...int) {
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for _, root := range []string{"t", "p"} {
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fmt.Printf("const _ = unsafe.Offsetof(%s", root)
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for _, n := range ns {
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fmt.Printf(".T%d", n)
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}
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// Does it involve an indirection?
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nlast := ns[len(ns)-1]
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nprev := 1
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if len(ns) > 1 {
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nprev = ns[len(ns)-2]
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}
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isIndirect := false
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for n := nlast / 2; n > nprev; n /= 2 {
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if n%2 == 1 {
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isIndirect = true
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break
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}
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}
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fmt.Print(")")
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if isIndirect {
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fmt.Print(` // ERROR "indirection"`)
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}
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fmt.Print("\n")
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}
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}
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