[Bug other/82352] New: link error 'defined in discarded section'

[holger.hopp at sap dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82352

            Bug ID: 82352
           Summary: link error 'defined in discarded section'
           Product: gcc
           Version: 7.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: other
          Assignee: unassigned at gcc dot gnu.org
          Reporter: holger.hopp at sap dot com
  Target Milestone: ---

I'm getting linker error
`...' referenced in section `...' of ..: defined in discarded section `...' of
...
with gcc-7 compiled code, that do not appear with gcc-5 or gcc-6.

Source:

typedef long unsigned int size_t;

class A
{
public :
  typedef enum { Zero = 0, One = 1 } tA;
  A(tA a) { m_a = a; }

private :
  tA m_a;
};

class B
{
public :
  void *operator new(size_t t) { return (void*)(42); };
};

class C
{
public:
  virtual void ffff () = 0;
};

class D
{
 public :
  virtual void g() = 0;
  virtual void h() = 0;
};

template<class T> class IIII: public T, public D
{
public:
 void ffff()
 {
   if (!m_i2) throw A(A::One);
 };

 void h()
 {
  if (m_i2) throw A(A::Zero);
 }

protected:
 virtual void g()
 {
  if (m_i1 !=0) throw A(A::Zero);
 };

private :
 int m_i1;
 void *m_i2;
};

class E
{
private:
    size_t m_e;
    static const size_t Max;

public:
    E& i(size_t a, size_t b, size_t c)
    {
        if ((a > Max) || (c > Max)) throw A(A::Zero );
        if (a + b > m_e) throw A(A::One );
        return (*this);
    }

  inline E& j(const E &s)
    {
      return i(0,0,s.m_e);
    }
};

class F : public C { };
class G : public C { };
class HHHH : public B, public F, public G { };

void k()
{
    HHHH *p = new IIII<HHHH>();
}

void l()
{
  E e1, e2;
  e1.j(e2);
}



Reproduce:

$ g++ -O2 -o t1.o -c t1.cpp && echo ok && objdump -t t1.o | grep ffffEv.part
ok
0000000000000000 l    d  .text.unlikely._ZN4IIIII4HHHHE4ffffEv.part.2  
0000000000000000 .text.unlikely._ZN4IIIII4HHHHE4ffffEv.part.2
0000000000000000 l     F .text.unlikely._ZN4IIIII4HHHHE4ffffEv.part.2  
0000000000000023 _ZN4IIIII4HHHHE4ffffEv.part.2

This symbol is causing the linker problem. Maybe this is already sufficient for
you.
You may get the final linker error as follows:

Slightly change source t1.cpp to t2.cpp:
- remove function g() (twice!)
- rename k() and l() by k2() and l2(2), respectively.

$ g++ -O2 -o t2.o -c t2.cpp && echo ok && objdump -t t2.o | grep ffffEv.part
ok
0000000000000000 l    d  .text.unlikely._ZN4IIIII4HHHHE4ffffEv.part.1  
0000000000000000 .text.unlikely._ZN4IIIII4HHHHE4ffffEv.part.1
0000000000000000 l     F .text.unlikely._ZN4IIIII4HHHHE4ffffEv.part.1  
0000000000000023 _ZN4IIIII4HHHHE4ffffEv.part.1

Symbol is named ...part.1 instead of ...part.2 in this case.

$ echo "int main() { return 0; }" | gcc -x c -c - -o main.o
$ g++ -o main main.o t1.o t2.o
`_ZN4IIIII4HHHHE4ffffEv.part.1' referenced in section `.text.unlikely' of t2.o:
defined in discarded section
`.text.unlikely._ZN4IIIII4HHHHE4ffffEv.part.1[_ZN4IIIII4HHHHE4ffffEv]' of t2.o
collect2: error: ld returned 1 exit status



Following works:
(1) gcc-5 and gcc-6
(2) gcc-7 with -O1
(3) marking ffff() with __attribute__((used))
    (found in https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65199)
(4) patch binutils in file bfd/elflink.c, function
_bfd_elf_default_action_discarded:
    remove the COMPLAIN flag


Nevertheless, it is probably a bug on gcc side, as in similar old bug 49665
with same linker error.