[Bug go/68255] New: cgo-generated constructor not being called

[vogt at linux dot vnet.ibm.com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68255

            Bug ID: 68255
           Summary: cgo-generated constructor not being called
           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: ---
              Host: s390x
            Target: s390x

Created attachment 36669
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36669&action=edit
Test case

With the latest code from the Gcc-6 development branch, constructor functions
in packages may not be called.  (Test code attached, run with

 $ tar xf cgo-ling.tar
 $ cd cgo-link
 $ GOPATH=$(pwd)
 $ cd src/main
 $ go build
 $ ./cgo-link"
==> NULL pointer acces, crash
.)




-- src/main/main.go --
package main 
import "pack" 
func main () { 
        pack.Foo() 
} 
-- END --

-- src/pack/pack.go --
package pack 

/* 
#include "c/c_code.c" 
*/ 
import "C" 

func Foo () { 
        println(C.p_cfunc) 
} 
-- END --

-- src/pack/c/c_code.c --
#include <stdio.h> 

typedef void (*cfunc_t)(void); 

static void cfunc(void) 
{ 
        printf("hallo\n"); 
} 

const cfunc_t p_cfunc = cfunc; 
-- END --

The init function generated by cgo to initialize p_cfunc is not placed into the
executable:

 $ go build -x

-- snip --
...

ar cru $WORK/libpack.a $WORK/pack/_obj/_go_.o $WORK/pack/_obj/_cgo_defun.o
$WOR\
K/pack/_obj/_cgo_export.o $WORK/pack/_obj/pack.cgo2.o

...

.../bin/gccgo -I $WORK -I .../cgo-link/pkg/gccgo_linux_s390x -c -g
-fgo-relativ\
e-import-path=_.../cgo-link/src/main -o $WORK/main/_obj/_go_.o ./main.go 
ar cru $WORK/libmain.a $WORK/main/_obj/_go_.o 

.../bin/gccgo -o $WORK/main/_obj/exe/a.out $WORK/main/_obj/_go_.o -Wl,-(
$WORK/\
libpack.a -Wl,-) -Wl,-E 
cp $WORK/main/_obj/exe/a.out main 
-- snip --

The linker invocation triggered with the final gccgo command disposes of the
init() function generated by cgo, so p_cfund ends up unitinialised.  The
problem goes away if I put _go_.o into the link group with libpack.a.

While it's possible to do the same in C, the specific problem with the go tool
and cgo is that you have no direct control over the linker invocation.  I'm not
sure whether this is a bad invocation of the linker or a bug in the linker, but
it should be possible to fic that in the sources of the go tool in build.go.

--

This is probably the same problem as here:
/show_bug.cgi?id=65134

But the workaround mentioned there won't work because the init function is
generated by cgo.