Re: Confusing meaning of --no-undefined

[Nick Clifton <nickc at redhat dot com>]

Hi Alan, Hi H.J.,

  I need your help/advice.  I took a look at the error reported by Jan
  Vroonhof:

    http://sources.redhat.com/ml/binutils/2003-02/msg00024.html

  concerning the fact that:

     ld --share --no-undefined foo.o bar.so

  does not report an undefined symbol in bar.so.

  It seemed to me that the problem was in elf_link_output_extsym()
  in bfd/elflink.h, where there is a test for unresolved symbols:

    /* If we are not creating a shared library and this symbol is
       referenced by a shared library but is not defined anywhere, then
       warn that it is undefined.  If we do not do this, the runtime
       linker will complain that the symbol is undefined when the
       program is run.  We don't have to worry about symbols that are
       referenced by regular files, because we will already have issued
       warnings for them.  */
    if (! finfo->info->relocateable
        && ! finfo->info->allow_shlib_undefined
        && ! finfo->info->shared
        && h->root.type == bfd_link_hash_undefined
        && (h->elf_link_hash_flags & ELF_LINK_HASH_REF_DYNAMIC) != 0
        && (h->elf_link_hash_flags & ELF_LINK_HASH_REF_REGULAR) == 0
        && ! elf_link_check_versioned_symbol (finfo->info, h))
      {

  This seemed wrong to me, since if we *are* creating a shared library
  we should also issue an error message unless allow_shlib_undefined
  is true.  So I changed the test like this:

Index: bfd/elflink.h
===================================================================
RCS file: /cvs/src/src/bfd/elflink.h,v
retrieving revision 1.204
diff -c -3 -p -w -r1.204 elflink.h
*** bfd/elflink.h	4 Feb 2003 12:49:57 -0000	1.204
--- bfd/elflink.h	11 Feb 2003 17:09:10 -0000
*************** elf_link_output_extsym (h, data)
*** 6096,6103 ****
       referenced by regular files, because we will already have issued
       warnings for them.  */
    if (! finfo->info->relocateable
!       && ! finfo->info->allow_shlib_undefined
!       && ! finfo->info->shared
        && h->root.type == bfd_link_hash_undefined
        && (h->elf_link_hash_flags & ELF_LINK_HASH_REF_DYNAMIC) != 0
        && (h->elf_link_hash_flags & ELF_LINK_HASH_REF_REGULAR) == 0
--- 6097,6103 ----
       referenced by regular files, because we will already have issued
       warnings for them.  */
    if (! finfo->info->relocateable
!       && (! finfo->info->shared || ! finfo->info->allow_shlib_undefined)
        && h->root.type == bfd_link_hash_undefined
        && (h->elf_link_hash_flags & ELF_LINK_HASH_REF_DYNAMIC) != 0
        && (h->elf_link_hash_flags & ELF_LINK_HASH_REF_REGULAR) == 0

  and sure enough the error message in Jan's test was now correctly
  generated.  When I ran the linker tests however, I discovered that
  this patch causes the ld-elfweak tests to fail:

     FAIL: ELF weak

  because of errors like this:

    /lib/libc.so.6: undefined reference to `_dl_lookup_versioned_symbol_skip@GLIBC_PRIVATE'

  Now I can patch up the testsuite to add the --allow-shlib-undefined
  switch (see second patch below), but is this the correct thing to
  do ?  You guys are more experienced with this area of the linker, so
  I would appreciate your advice.

Cheers
        Nick

Index: ld/testsuite/ld-elfweak/elfweak.exp
===================================================================
RCS file: /cvs/src/src/ld/testsuite/ld-elfweak/elfweak.exp,v
retrieving revision 1.4
diff -c -3 -p -w -r1.4 elfweak.exp
*** ld/testsuite/ld-elfweak/elfweak.exp	30 Jul 2002 07:41:13 -0000	1.4
--- ld/testsuite/ld-elfweak/elfweak.exp	11 Feb 2003 17:26:25 -0000
*************** proc build_lib {test libname objs dynsym
*** 281,287 ****
        set files "$files $tmpdir/$obj"
      }
  
!     if {![ld_link $ld $tmpdir/$libname.so "$shared $files"]} {
  	fail $test
  	return
      }
--- 281,287 ----
        set files "$files $tmpdir/$obj"
      }
  
!     if {![ld_link $ld $tmpdir/$libname.so "--allow-shlib-undefined $shared $files"]} {
  	fail $test
  	return
      }
*************** if ![ld_compile "$CC $CFLAGS" $srcdir/$s
*** 391,397 ****
      return
  }
  
! if {![ld_link $ld $tmpdir/libbar.so "$shared $tmpdir/bar.o"]} {
      fail "ELF weak"
      return
  }
--- 391,397 ----
      return
  }
  
! if {![ld_link $ld $tmpdir/libbar.so "$shared --allow-shlib-undefined $tmpdir/bar.o"]} {
      fail "ELF weak"
      return
  }
*************** if ![ld_compile "$CC $CFLAGS" $srcdir/$s
*** 426,442 ****
      return
  }
  
! if {![ld_link $ld $tmpdir/libfoo1a.so "$shared $tmpdir/foo1a.o"]} {
      fail "ELF weak"
      return
  }
  
! if {![ld_link $ld $tmpdir/libfoo1b.so "$shared $tmpdir/foo1b.o"]} {
      fail "ELF weak"
      return
  }
  
! if {![ld_link $ld $tmpdir/libbar1a.so "$shared $tmpdir/bar1a.o $tmpdir/libfoo1a.so"]} {
      fail "ELF weak"
      return
  }
--- 426,442 ----
      return
  }
  
! if {![ld_link $ld $tmpdir/libfoo1a.so "$shared --allow-shlib-undefined $tmpdir/foo1a.o"]} {
      fail "ELF weak"
      return
  }
  
! if {![ld_link $ld $tmpdir/libfoo1b.so "$shared --allow-shlib-undefined $tmpdir/foo1b.o"]} {
      fail "ELF weak"
      return
  }
  
! if {![ld_link $ld $tmpdir/libbar1a.so "$shared --allow-shlib-undefined $tmpdir/bar1a.o $tmpdir/libfoo1a.so"]} {
      fail "ELF weak"
      return
  }