cmd/cgo: link failure when referencing standard COM GUID (non-function external symbol in a DLL) #9916
Comments
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The same/a similar thing happens if the reference to package main
import "fmt"
// #cgo LDFLAGS: -luuid
// extern void *getIUnknown(void);
import "C"
func main() {
fmt.Printf("IID_IUnknown is at %p", C.getIUnknown())
}#define CINTERFACE
#include <windows.h>
void *getIUnknown(void)
{
return (void *) (&IID_IUnknown);
} |
mikioh
changed the title
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You need to set INITGUID before include. package main
import "fmt"
// #define INITGUID
// #include <objidl.h>
// #cgo LDFLAGS: -luuid
import "C"
func main() {
fmt.Printf("IID_IUnknown is at %p", &C.IID_IUnknown)
}Btw, If you want to call COM/OLE from go, see also https://github.com/mattn/go-ole |
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Well that fixed the build; thanks. What exactly does I don't need to use COM from Go; I wrote a new Table control for package ui and its accessibility code uses COM (as that's how accessibility is exposed on Windows) but that's all on the C side. |
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Wait, so is this really the only scenario in which the above error will happen? |
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@andlabs when you use gcc, you have to play by its rules. If you have a problem will reopen this issue. Alex |
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IID_IUnknown is imported from dll. So it shouldn't be specified as cgo_import_static. |
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Anyone, could you please re-open this? |
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Sorry, I updated CL. |
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@alexbrainman I'm sorry, could you explain what you mean? @mattn ah, thanks for the clarification :) |
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@andlabs gcc is not part of Go. gcc is another big world. If you want to go there, you need to understand how it works. I don't know how it works. Your original issue was about IID_IUnknown structure. You don't really need to use gcc to access IID_IUnknown. |
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I know that; I don't know how my question was about gcc, as this happens with cgo and it clearly happens at the 8l step, not at gcc... |
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I think #4069 should fix also fix this. Please try again after that issue
is closed.
(Should be soon, as I just need to address one last comment in the CL
series.)
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I'm not sure, but if you didn't fix link phase for external library to use |
package main
/*
#include <stdio.h>
#include <objbase.h>
#cgo LDFLAGS: -luuid
int ccc = 3;
*/
import "C"
import "log"
import "os"
func test9916(t *log.Logger) {
v := C.IID_IUnknown
log.Println(v)
if v.Data1 != 0 {
t.Fatalf("Data1 %v", v)
}
if v.Data2 != 0 {
t.Fatalf("Data2 %v", v)
}
if v.Data3 != 0 {
t.Fatalf("Data3 %v", v)
}
if v.Data4[0] != 192 {
t.Fatalf("Data4[0] %v", v)
}
if v.Data4[7] != 70 {
t.Fatalf("Data4[7] %v", v)
}
println(C.ccc)
}
func main() {
test9916(log.New(os.Stdout, "", 0))
}See https://go-review.googlesource.com/#/c/5253/3/src/cmd/go/build.go On windows, |
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#4069 has been fixed on tip, please retry this.
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Thanks for confirmation! |
IID_IUnknownis a GUID that COM uses to refer to theIUnknowninterface (IUnknownis to COM asinterface{}is to Go). These GUIDs are defined in uuid.dll, a system DLL that you link against programs that want to use COM. This confuses Go's linker:I'm not sure if this specifically happens for these UUIDs or for any symbol in a DLL (or other shared object) hat isn't a function.
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