[PATCH] bfd: Fix 64-bit relocation handling for a.out

[Gunther Nikl]

[This is a slightly edited version of the previous mail which was blocked
by sourceware]

Hello Nick,

> Hi Gunther,
> 
> > I have an update which ensures only supported sizes are permitted. 
> > Thoughts?
> 
> I like it.  I only have one comment:
> 
> > +  switch (bfd_get_reloc_size (g->howto))
> > +    {
> > +      default:
> > +	_bfd_error_handler (_("%pB: unsupported relocation size"), abfd);
> 
> vs...
> 
> > +	switch (bfd_get_reloc_size (howto))
> > +	  {
> > +	    default:
> > +	      abort ();
> 
> I far prefer error messages (and error return codes, if available) to 
> calling abort.  As a user I find having an error message telling me at
> least something about what is wrong to be much more useful than an a
> abort referring to source code that I may not even have available.

I agree that an error message is nicer than an abort. I have chosen
abort in the second case since other places in the modified function do
the same.

However, I now believe that this hunk can be dropped. The used bfd
object is an a.out type as the aout_backend_data is used all over the
place with that bfd object in this function. Thus the howto is from
howto_table_std and no unsupported size is possible at this time.

Attached is an updated patch there the aout_link_reloc_link_order change
is removed.

Regards,
Gunther

---
2020-05-XX  Gunther Nikl  <gnikl@justmail.de>

	* aoutx.h (NAME (aout, swap_std_reloc_out)): Reject an unsupported
	relocation size.

diff --git a/bfd/aoutx.h b/bfd/aoutx.h
index d5457461ab..09d61b1c2d 100644
--- a/bfd/aoutx.h
+++ b/bfd/aoutx.h
@@ -1946,10 +1946,19 @@ NAME (aout, swap_std_reloc_out) (bfd *abfd,
 
   BFD_ASSERT (g->howto != NULL);
 
-  if (bfd_get_reloc_size (g->howto) != 8)
-    r_length = g->howto->size;	/* Size as a power of two.  */
-  else
-    r_length = 3;
+  switch (bfd_get_reloc_size (g->howto))
+    {
+      default:
+	_bfd_error_handler (_("%pB: unsupported relocation size"), abfd);
+	bfd_set_error (bfd_error_bad_value);
+	return;
+      case 1: case 2: case 4:
+	r_length = g->howto->size;	/* Size as a power of two.  */
+	break;
+      case 8:
+	r_length = 3;
+	break;
+    }
 
   r_pcrel  = (int) g->howto->pc_relative; /* Relative to PC?  */
   /* XXX This relies on relocs coming from a.out files.  */
---