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https://github.com/golang/go
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f582778ee9
Currently, the compiler will emit any const that doesn't fit in an
int64 to go_asm.h like
#define const_stackPreempt constant.intVal{val:(*big.Int)(0xc000c06c40)}
This happens because dumpasmhdr formats the constant.Value using the
verb "%#v". Since constant.Value doesn't implement the GoString()
method, this just prints the Go-syntax representation of the value.
This happens to work for small integer constants, which go/constant
represents directly as an int64, but not for integer constants that
don't fit in an int64, which go/constant represents as a big.Int.
Make these constants usable by changing the formatting verb to "%v",
which will call the String() method, giving a reasonable result in all
cases.
Change-Id: I365eeb88c8acfc43ff377cc873432269bde3f541
Reviewed-on: https://go-review.googlesource.com/c/go/+/359954
Trust: Austin Clements <austin@google.com>
Run-TryBot: Austin Clements <austin@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
67 lines
1.5 KiB
Go
67 lines
1.5 KiB
Go
// Copyright 2021 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package main
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import "unsafe"
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const (
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smallInt = 42
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// For bigInt, we use a value that's too big for an int64, but still
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// fits in uint64. go/constant uses a different representation for
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// values larger than int64, but the cmd/asm parser can't parse
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// anything bigger than a uint64.
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bigInt = 0xffffffffffffffff
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stringVal = "test"
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)
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var (
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smallIntAsm int64
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bigIntAsm uint64
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stringAsm [len(stringVal)]byte
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)
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type typ struct {
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a uint64
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b [100]uint8
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c uint8
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}
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var (
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typSize uint64
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typA, typB, typC uint64
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)
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func main() {
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if smallInt != smallIntAsm {
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println("smallInt", smallInt, "!=", smallIntAsm)
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}
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if bigInt != bigIntAsm {
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println("bigInt", uint64(bigInt), "!=", bigIntAsm)
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}
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if stringVal != string(stringAsm[:]) {
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println("stringVal", stringVal, "!=", string(stringAsm[:]))
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}
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// We also include boolean consts in go_asm.h, but they're
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// defined to be "true" or "false", and it's not clear how to
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// use that in assembly.
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if want := unsafe.Sizeof(typ{}); want != uintptr(typSize) {
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println("typSize", want, "!=", typSize)
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}
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if want := unsafe.Offsetof(typ{}.a); want != uintptr(typA) {
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println("typA", want, "!=", typA)
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}
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if want := unsafe.Offsetof(typ{}.b); want != uintptr(typB) {
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println("typB", want, "!=", typB)
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}
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if want := unsafe.Offsetof(typ{}.c); want != uintptr(typC) {
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println("typC", want, "!=", typC)
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}
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}
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