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x/tools/go/loader: fails to correctly determine integer type size based on GOARCH #26257

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kortschak opened this issue Jul 7, 2018 · 1 comment
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x/tools/go/loader: fails to correctly determine integer type size based on GOARCH #26257

kortschak opened this issue Jul 7, 2018 · 1 comment
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@kortschak
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What version of Go are you using (go version)?

go version go1.10.3 linux/arm

Does this issue reproduce with the latest release?

This is not feasible to test.

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

GOARCH="arm"
GOOS="linux"

What did you do?

Run go/loader to load a package on an arm device.

package main

import (
	"go/token"
	"log"

	"golang.org/x/tools/go/loader"
)

func main() {
	var conf loader.Config
	conf.Fset = token.NewFileSet()
	conf.Import("foo")
	_, err := conf.Load()
	if err != nil {
		log.Fatal(err)
	}
}

The package in foo makes reference to the size of int.

package main

const (
	MaxInt  = 1<<(IntBits-1) - 1
	IntBits = 1 << (^uint(0)>>32&1 + ^uint(0)>>16&1 + ^uint(0)>>8&1 + 3)
)

func main() {
	var u32 uint32
	u32 = MaxInt
	println(u32)
}

This is a valid Go program;

$ go run foo.go 
2147483647

but running the loader program above results in

$ go run loader.go 
/home/pi/src/foo/foo.go:10:8: MaxInt (untyped int constant 9223372036854775807) overflows uint32
2018/07/07 12:09:36 couldn't load packages due to errors: foo
exit status 1

What did you expect to see?

No output.

What did you see instead?

The error above and a non-zero exit status.
@gopherbot gopherbot added this to the Unreleased milestone Jul 7, 2018
@kortschak kortschak mentioned this issue Jul 7, 2018
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@jimmyfrasche
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This is correct.

go/loader uses go/types. go/types is sufficient to reproduce: https://play.golang.org/p/Vy-hXe7A7Q6

There is no error if you instruct it to use sizes for arm explicitly, however: https://play.golang.org/p/tYNZ4VEkCOw (or any other platform with a 4-byte word size).

If you don't set an explicit Size in the typechecker config, go/types uses SizesFor("gc", "amd64") regardless of the platform it's running on, hence the overflow.

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@kortschak @jimmyfrasche @gopherbot