On Wed, 2020-09-09 at 13:21 +0200, Jan Mercl wrote:
>
>
> On Wed, Sep 9, 2020 at 1:09 PM 'Dan Kortschak' via golang-nuts <
> [email protected]> wrote:
>
> > What does cgo -godefs give you? On my amd64 and arm64 I get this:
> >
> > ```
> > ~/cznic $ cat main.go
> > package main
> >
> > /*
> > struct s {
> > long long i;
> > } x;
> > */
> > import "C"
> >
> > type S struct {
> > i int64
> > }
> >
> > type C_s C.struct_s
> >
> > ~/cznic $ go tool cgo -godefs main.go
> > // Code generated by cmd/cgo -godefs; DO NOT EDIT.
> > // cgo -godefs main.go
> >
> > package main
> >
> > type S struct {
> > i int64
> > }
> >
> > type C_s struct {
> > I int64
> > }
> > ```
>
> amd64
> =====================================================================
> ====
>
> jnml@e5-1650:~/tmp$ go version
> go version go1.15.1 linux/amd64
> jnml@e5-1650:~/tmp$ cat main.go
> package main
>
> /*
> struct s {
> long long i;
> } x;
> */
> import "C"
>
> type S struct {
> i int64
> }
>
> type C_s C.struct_s
> jnml@e5-1650:~/tmp$ go tool cgo -godefs main.go
> // Code generated by cmd/cgo -godefs; DO NOT EDIT.
> // cgo -godefs main.go
>
> package main
>
> type S struct {
> i int64
> }
>
> type C_s struct {
> I int64
> }
> jnml@e5-1650:~/tmp$
>
> arm
> =====================================================================
> ======
>
> pi@raspberrypi:~/src/tmp.tmp $ go version
> go version go1.15.1 linux/arm
> pi@raspberrypi:~/src/tmp.tmp $ cat main.go
> package main
>
> /*
> struct s {
> long long i;
> } x;
> */
> import "C"
>
> type S struct {
> i int64
> }
>
> type C_s C.struct_s
> pi@raspberrypi:~/src/tmp.tmp $ go tool cgo -godefs main.go
> // Code generated by cmd/cgo -godefs; DO NOT EDIT.
> // cgo -godefs main.go
>
> package main
>
> type S struct {
> i int64
> }
>
> type C_s struct {
> I int64
> }
> pi@raspberrypi:~/src/tmp.tmp $
>
> No difference between the outputs AFAICT. Seems good to me.
>
>
I think it comes down to these lines in src/cmd/internal/sys/arch.go
[1]
```
var ArchARM = &Arch{
Name: "arm",
Family: ARM,
ByteOrder: binary.LittleEndian,
PtrSize: 4,
RegSize: 4,
MinLC: 4,
}
var ArchARM64 = &Arch{
Name: "arm64",
Family: ARM64,
ByteOrder: binary.LittleEndian,
PtrSize: 8,
RegSize: 8,
MinLC: 4,
}
```
this line in src/cmd/compile/internal/gc/main.go [2]
```
Widthreg = thearch.LinkArch.RegSize
```
and these lines in src/cmd/compile/internal/gc/align.go [3]
```
case TINT64, TUINT64, TFLOAT64:
w = 8
t.Align = uint8(Widthreg)
```
[1]https://golang.org/src/cmd/internal/sys/arch.go
[2]https://golang.org/src/cmd/compile/internal/gc/main.go
[3]https://golang.org/src/cmd/compile/internal/gc/align.go
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