[Bug go/67976] New: Cgo + Gccgo not working like Cgo + Golang?

[Bug go/67976] New: Cgo + Gccgo not working like Cgo + Golang?

[vogt at linux dot vnet.ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67976

            Bug ID: 67976
           Summary: Cgo + Gccgo not working like Cgo + Golang?
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: go
          Assignee: ian at airs dot com
          Reporter: vogt at linux dot vnet.ibm.com
                CC: cmang at google dot com
  Target Milestone: ---

The authors of the Ethereum project seem to assume that cgo can handle the code
below in a sensible way, but when using the -gccgo option that is not the case.

-- snip --
package foo 

/* 
int foo_cgo(unsigned); 
*/ 
import "C" 
import "unsafe" 

//export foo 
func foo(x C.unsigned) C.int { 
        return 0 
} 

func () bar() { 
        _ = unsafe.Pointer(C.foo_cgo) 
} 
-- snip --

Running this through

  $ mkdir _obj
  $ cgo -objdir _obj -gccgo foo.go

Results in this code in _cgo_main.c:

  extern char foo_cgo[]; 
  void *_cgohack_foo_cgo = foo_cgo; 
  #include "_cgo_export.h"

And this line in _cgo_export.h:

  int foo_cgo(unsigned); 

Redeclaring foo_cgo results in an error message when trying to compile
_cgo_main.c.

Maybe _cgo_export.h should simply be emitted to _cgo_main.c *before* all the
declarations?

[Bug go/67976] Cgo + Gccgo not working like Cgo + Golang?

[vogt at linux dot vnet.ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67976

--- Comment #1 from Dominik Vogt <vogt at linux dot vnet.ibm.com> ---
When cgo encounters the "C.foo_cgo", it determines that it must be a variable,
but finds no C definition, so it generates "extern char foo_cgo[]" (out.go) as
the type.  This conflicts with the declaration in the comment at the beginning
of the file.  Replacing

/* 
int foo_cgo(unsigned); 
*/ 

with

/* 
extern char foo_cgo[];
*/

Makes this code compile for me.  Is this kind of declaration supported by the
cgo version from the golang repository?  (If not, what would the symbol
C.foo_cgo be good for).

[Bug go/67976] Cgo + Gccgo not working like Cgo + Golang?

[ian at airs dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67976

--- Comment #2 from Ian Lance Taylor <ian at airs dot com> ---
This is probably https://golang.org/issue/8945 , which is fixed in the gc
repository but not in the gccgo repository.  That fix should come in when I
merge in the Go 1.5 sources.

[Bug go/67976] Cgo + Gccgo not working like Cgo + Golang?

[vogt at linux dot vnet.ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67976

--- Comment #3 from Dominik Vogt <vogt at linux dot vnet.ibm.com> ---
When do you expect Go 1.5 to be merged?

[Bug go/67976] Cgo + Gccgo not working like Cgo + Golang?

[vogt at linux dot vnet.ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67976

--- Comment #4 from Dominik Vogt <vogt at linux dot vnet.ibm.com> ---
The patch behind the link in comment 2 fixes the problem.