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

Alan Modra amodra@gmail.com
Mon Feb 3 00:05:51 GMT 2025 
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.

> > >  The linker created sections are excluded when estimating
> > > output section layout as sizing dynamic sections may change linker
> > > created sections.
> >
> > This logic also ought to go in the x86 backend to handle whatever
> > peculiarities are necessary for x86 linker created sections.
> 
> I will drop this change.
> 
> > --
> > Alan Modra
> 
> 
> 
> -- 
> H.J.

-- 
Alan Modra
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