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cmd/cgo: `unexpected: 8-byte pointer type` errors with GOARCH=arm #12442

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jacobsa opened this issue Sep 1, 2015 · 4 comments

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@jacobsa
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commented Sep 1, 2015

I'm attempting to regenerate the darwin/arm code for golang.org/x/sys/unix from the latest iOS SDK, but running into a problem with go tool cgo -godefs on that architecture. Here is a file that reproduces the issue:

package blah

/*
typedef struct foo {
    void* a;
} foo_t;
*/
import "C"

type Foo_t C.struct_foo

Put that in foo.go and this happens:

% GOARCH=arm go tool cgo -godefs foo.go
/Users/jacobsa/go/src/golang.org/x/sys/unix/foo.go:10:12: unexpected: 8-byte pointer type - *void

I'm not sure what that message means in this context, since I haven't given cgo any input on the size of that pointer except by setting GOARCH. I wonder if I've misconfigured something, but can't find any relevant documentation so I'm not sure. It may be relevant that this doesn't happen when GOARCH is set to 386.

This happens at tip on OS X:

% go version
go version devel +dd42eff Tue Sep 1 22:13:16 2015 +0000 darwin/amd64

@ianlancetaylor ianlancetaylor added this to the Go1.6 milestone Sep 2, 2015

@ianlancetaylor

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commented Sep 2, 2015

cgo works by building a C file, compiling it, and examining the debug info. In this case it is complaining because it expects pointer types to have the size of a pointer. For GOARCH=386 a pointer is obviously 4 bytes, but the debug info is indicating that the pointer is 8 bytes.

In order to use cgo in a cross-compilation situaiton like this one, you need to set CC tin the environment o a cross-compiler for ARM. Look for "when cross-compiling" in https://golang.org/cmd/cgo .

I'm going to close this on the assumption that you didn't set CC. Please reopen if I've misunderstood.

@jacobsa

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commented Sep 2, 2015

@iant: Thanks. Do you happen to know what an appropriate value of CC is for building arm and arm64 respectively on OS X?

@minux

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commented Sep 2, 2015

@jacobsa

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commented Sep 2, 2015

Whoa, that's exactly what I've been looking for this whole time! Thank you. :-)

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