Re: debugging problem with musl ld and qemu-ppc

[Rich Felker <dalias@libc.org>]

On Sat, Nov 01, 2014 at 10:41:28PM +0100, Felix Janda wrote:
> Rich Felker wrote:
> > On Sun, Oct 19, 2014 at 10:29:35PM +0200, Felix Janda wrote:
> [..]
> > > 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].
> > 
> > Nice job tracking this down. If there's not a reason you need this
> > specific construct, I would just avoid it, but really the above hack
> > should be removed from binutils. There are all sorts of asm constructs
> > that are specific to one ABI, and the presence of something that seems
> > to be specific to one ABI is not a justification for ignoring the
> > user's choice of link options.
> 
> The construct is used in a file in gmp and this caused my home-built gcc
> to crash. I'm wondering why other people have not hit this issue. (I
> guess it is because they didn't use dynamic linking.)

Could you give a link to the code where it's used? It would be nice to
see if this is actually something broken that's assuming the
insecure-plt ABI or whether it's just binutils misinterpreting it and
making trouble for us.

Rich