Re: debugging problem with musl ld and qemu-ppc

[Felix Janda <felix.janda@posteo.de>]

Felix Janda wrote:
> Rich Felker wrote:
[..]
> > What I'm not clear about is the cause for why the linker is forcing
> > you back to the bss-plt model. It might be a matter of the strange
> > relocation type you put in a.s:
> > 
> > 00000000 <.text>:
> >    0:   48 00 00 00     b       0x0
> >                            0: R_PPC_LOCAL24PC      _GLOBAL_OFFSET_TABLE_
> 
> The problem caused a self-compiled native gcc to crash because the file
> "mpn/powerpc32/elf.m4" (used to generate some assembly) in the gmp tree 
> contains a similar instruction.
> 
> I've found the part in binutils emitting the warning and will try to see
> why it forces bss-plt.

This seems to be caused by the part starting from lines 4267 in [1]

	  /* This refers only to functions defined in the shared library.  */
	case R_PPC_LOCAL24PC:
	  if (h != NULL && h == htab->elf.hgot && htab->plt_type == PLT_UNSET)
	    {
	      htab->plt_type = PLT_OLD;
	      htab->old_bfd = abfd;
	    }

I think it was added to be helpful and detect the construction

bl _GLOBAL_OFFSET_TABLE_@local-4
mflr r30

intended to load a pointer to the got into r30, which no longer works
with secure-plt. See [2].

Felix

[1]: http://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;a=blob;f=bfd/elf32-ppc.c;h=04c2d6ad60b4122eb1727e932cfcda035feeac68;hb=HEAD
[2]: http://www.sourceware.org/ml/binutils/2005-05/txt00011.txt