package main
func gwrite(b []byte) {
        n := copy(gp.writebuf[len(gp.writebuf):cap(gp.writebuf)], b)
}

 ~/install/bin/gccgo testcase.go 
testcase.go:5:12: error: reference to undefined name ‘gp’
  n := copy(gp.writebuf[len(gp.writebuf):cap(gp.writebuf)], b)
            ^
testcase.go:5:28: error: reference to undefined name ‘gp’
  n := copy(gp.writebuf[len(gp.writebuf):cap(gp.writebuf)], b)
                            ^
testcase.go:5:45: error: reference to undefined name ‘gp’
  n := copy(gp.writebuf[len(gp.writebuf):cap(gp.writebuf)], b)
                                             ^
testcase.go:5:2: error: ‘n’ declared and not used
  n := copy(gp.writebuf[len(gp.writebuf):cap(gp.writebuf)], b)
  ^
go1: internal compiler error: Segmentation fault
0x107f0433 crash_signal
        ../../gcc/toplev.c:383
0x1026bf80 Array_type::get_value_pointer(Gogo*, Expression*) const
        ../../gcc/go/gofrontend/types.cc:6163
0x101d4ddf Builtin_call_expression::do_get_backend(Translate_context*)
        ../../gcc/go/gofrontend/expressions.cc:8353
0x101c2c47 Expression::get_backend(Translate_context*)
        ../../gcc/go/gofrontend/expressions.cc:411
0x101d846b Type_conversion_expression::do_get_backend(Translate_context*)
        ../../gcc/go/gofrontend/expressions.cc:3340
0x101c2c47 Expression::get_backend(Translate_context*)
        ../../gcc/go/gofrontend/expressions.cc:411
0x1020aebb Variable::get_init(Gogo*, Named_object*)
        ../../gcc/go/gofrontend/gogo.cc:6195
0x1025ec8f Variable_declaration_statement::do_get_backend(Translate_context*)
        ../../gcc/go/gofrontend/statements.cc:267
0x10253797 Statement::get_backend(Translate_context*)
        ../../gcc/go/gofrontend/statements.cc:141
0x10216e4f Block::get_backend(Translate_context*)
        ../../gcc/go/gofrontend/gogo.cc:5648
0x10217bd7 Function::build(Gogo*, Named_object*)
        ../../gcc/go/gofrontend/gogo.cc:5254
0x10218503 Named_object::get_backend(Gogo*, std::vector<Bexpression*, std::allocator<Bexpression*> >&, std::vector<Btype*, std::allocator<Btype*> >&, std::vector\
<Bfunction*, std::allocator<Bfunction*> >&)
        ../../gcc/go/gofrontend/gogo.cc:6973
0x1022058f Gogo::write_globals()
        ../../gcc/go/gofrontend/gogo.cc:1289
0x102045bf go_write_globals()
        ../../gcc/go/gofrontend/go.cc:147
0x101fe727 go_langhook_write_globals
        ../../gcc/go/go-lang.c:463
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <http://gcc.gnu.org/bugs.html> for instructions.