Re: Reviving SH FDPIC target

[Rich Felker <dalias@libc.org>]

On Thu, Sep 10, 2015 at 11:49:19PM -0400, Rich Felker wrote:
> On Fri, Sep 04, 2015 at 04:16:40PM -0400, Rich Felker wrote:
> > On Thu, Sep 03, 2015 at 11:53:45AM -0400, Rich Felker wrote:
> > > On Thu, Sep 03, 2015 at 02:58:39PM +0000, Joseph Myers wrote:
> > > > On Wed, 2 Sep 2015, Rich Felker wrote:
> > > > 
> > > > > So if __fpscr_values was the only reason for patch 1/3 in the FDPIC
> > > > > patchset, I think we can safely drop it. And patch 2/3 was already
> > > > > committed, so 3/3, the one I was originally looking at, seems to be
> > > > > all we need. It was approved at the time, so I'll proceed with merging
> > > > > it with 5.2.0.
> > > > 
> > > > Well, obviously if trying dropping patch 1/3 you need to remove everything 
> > > > related to use_initial_val (the feature added in patch 1/3) from patch 
> > > > 3/3.
> > > 
> > > As far as I can tell, the only "use" of use_initial_val is defining
> > > the pseudo-instruction in the md file, which causes the code in patch
> > > 1/3 to use it. I see no other references to it. As I understand, the
> > > breakage from not having it (in the original 4.5-era patch) would be
> > > when introducing references to __fpscr_values later, and no longer
> > > having the GOT pointer, but that code is gone now.
> > 
> > I have this basically working -- obviously no heavy testing yet, and
> > the specs glue is not sufficient to make it practical for others to
> > try it yet, so it'll be a little longer til I have something to post.
> 
> I'm running into a problem with crtstuff.c: the references to
> __TMC_END__, etc. end up using @GOTOFF relocations which the linker
> then rejects. Is this a linker bug or something I need to fix in the
> target code to avoid generating @GOTOFF relocations? Since crtbegin.o
> has no information about what section __TMC_END__ will be in when it's
> defined, I don't see a lot of options except to avoid using @GOTOFF
> entirely for symbols that aren't defined in the same TU.

Well, that was easier than I thought, at least for a quick hack: I
added:

  SYMBOL_REF_EXTERNAL_P(orig) || DECL_SECTION_NAME(SYMBOL_REF_DECL(orig))

to the list of conditions for using @GOT instead of @GOTOFF. This may
actually be optimal under the constraints we have...

Rich