Re: [PATCH 4/8] section-select: Completely rebuild matches

[Michael Matz <matz@suse.de>]

Hey,

On Tue, 29 Nov 2022, Alan Modra wrote:

> > > That's a problem.  The got header is created in the .got of "linker
> > > stubs", and code setting the value of .TOC. assumes that the header
> > > will be located first in the .got output section.  This ties in with
> > > where ld.so expects to find the header too.
> > 
> > I see.  But then why is the testcase (and linker script?) not using
> > 
> >   .got { *(.got) *(.toc) }
> > 
> > ?  The way it's written right now means "for each file, first its .got 
> > then its .toc, intermixed", i.e. file1.got, file1.toc, file2.got, 
> > file2.toc ...
> 
> Yes.  That's the way we want it.  When linking small model code with a
> total GOT/TOC of over 64k, the linker splits the TOC into multiple
> pieces with r2 adjusting stubs inserted on calls between files that
> use different pieces of the TOC.  That scheme wouldn't work if a
> file's .got entries were placed in a different piece of the TOC to the
> file's .toc entries.

Ah, nifty.  Something like that occurred to me yesterday as well, and 
either way, rewriting the linker script like above wouldn't have helped 
this problem anyway, as long as "linker stubs".got would have been created 
late it would always have been placed at the end of the list.

Although one could pedantically argue that those late-created sections 
being placed at the end would indeed conform to "as they are found in the 
linker input", I won't belabor that point.  Complete rebuilding it is, 
performance-wise it's a wash :)


Ciao,
Michael.