Checkptr=0

[stephen.t....@gmail.com]

Hello,

I'm following the latest changes on the development tree and have noticed that the compiler flag "checkptr=0" is currently not having any effect. Has this flag been deprecated or is this just a temporary problem?

Currently, this flag is required when race checking software that uses go-gl. https://github.com/go-gl/gl/issues/124

Regards

Stephen Illingworth

[Ian Lance Taylor]

I don't think anything has intentionally changed in this area. Can
you give an example of how the behavior has changed? Thanks.

Ian

[stephen.t....@gmail.com]

On Tuesday, March 23, 2021 at 6:54:42 PM UTC Ian Lance Taylor wrote:

 

I don't think anything has intentionally changed in this area. Can
you give an example of how the behavior has changed? Thanks.

Running the race detector will turn on the checkptr check. Which is good but will result in a

panic in projects that convert uintptr to unsafe.Pointer in a suspicious manner. An example

of such a project is go-gl.

If we still want to run the race check  we can get around the problem by turning off checkptr:

    go run -race -gcflags=all=-d=checkptr=0 .

If we don't turn it off, we see a panic:

    fatal error: checkptr: pointer arithmetic computed bad pointer value

We see this in every version of Go since checkptr was introduced. This is fine and exactly

the behaviour we would expect.

However, in the current development tree. Setting checkptr=0 has no effect and we see the same panic as we

would if we didn't turn off the check. In other words,

    go run -race .

is the same as

    go run -race -gcflags=all=-d=checkptr=0 .

The simplest reproducible example I know of is the imgui-go-examples project:

    https://github.com/inkyblackness/imgui-go-examples

From the "cmd/example_sdl_opengl3" directory:

    go run -race -gcflags=all=-d=checkptr=0 -tags='sdl' .

will cause the panic when using the development compiler but not when using 1.16 etc.

Stephen

[Ian Lance Taylor]

Thanks. I sent https://golang.org/cl/304253 to fix this.

Ian