[PATCH] ld: Estimate output section layout before sizing dynamic sections

[Alan Modra]

On Mon, Feb 03, 2025 at 08:14:59AM +0800, H.J. Lu wrote:
> On Mon, Feb 3, 2025 at 8:05 AM Alan Modra <amodra@gmail.com> wrote:
> >
> > On Mon, Feb 03, 2025 at 07:34:01AM +0800, H.J. Lu wrote:
> > > On Mon, Feb 3, 2025 at 6:29 AM Alan Modra <amodra@gmail.com> wrote:
> > > >
> > > > On Sat, Feb 01, 2025 at 04:53:30PM +0800, H.J. Lu wrote:
> > > > > When sizing dynamic sections, elf_x86_64_scan_relocs converts GOTPCREL
> > > > > relocations to R_X86_64_PC32, R_X86_64_32S or R_X86_64_32 for local
> > > > > symbols.  But at that time, since the output section layout is unknown,
> > > > > the local symbol values can't be determined.  Later linker issues an
> > > > > error if the converted relocation overflows when resolving relocations
> > > > > against these local symbols.  Update the linker so that an ELF target
> > > > > can opt-in to estimate output section layout before sizing dynamic
> > > > > sections.
> > > >
> > > > I think that is the wrong way to go.  A single backend_data bit
> > > > controlling prelim sizing is likely not flexible enough.  It's far
> > > > better I think to implement an x86 before_allocation override hook
> > > > rather than trying to put the code in ldelf_before_allocation.
> > >
> > > This means that the x86_64 backend needs to duplicate the whole
> > > function so that it can do prelim sizing just before sizing dynamic sections.
> > > It can be easily out of sync when ldelf_before_allocation is changed.
> > > Is there a way to avoid it?
> >
> > Why would you need to duplicate the whole function?  Just call it.
> > See emultemp/ppc64elf.em.
> 
> It doesn't work for x86-64 since prelim sizing must be done just before
> sizing dynamic sections.  How about this

Explain "doesn't work".  How do the very few things that happen in
ldelf_before_allocation before the place you want to add another hook,
affect prelim sizing?

-- 
Alan Modra