Re: The trouble with __weak and objtool got worse

[Segher Boessenkool <segher@kernel.crashing.org>]

On Sat, Apr 16, 2022 at 08:20:06AM -0500, Segher Boessenkool wrote:
> On Sat, Apr 16, 2022 at 12:59:05PM +0200, Peter Zijlstra wrote:
> > On Fri, Apr 15, 2022 at 01:22:29PM -0500, Segher Boessenkool wrote:
> > > On Fri, Apr 15, 2022 at 01:19:04PM +0200, Peter Zijlstra wrote:
> > > > The other option seems to be to have objtool add section symbols it
> > > > needs, however due to ELF being a total PITA and requiring all LOCAL
> > > > symbols to be before GLOBAL symbols, this would mean re-ordering the
> > > > whole symbol table (I have the code somewhere :-/).
> > > 
> > > ELF requires no such thing?  Where do you see this?
> > 
> > The first google hit:
> > 
> >   https://docs.oracle.com/cd/E23824_01/html/819-0690/chapter6-79797.html
> > 
> > which has:
> > 
> >   "In each symbol table, all symbols with STB_LOCAL binding precede the
> >   weak symbols and global symbols. As Sections describes, a symbol table
> >   section's sh_info section header member holds the symbol table index for
> >   the first non-local symbol."
> 
> That is not the ELF spec, and it is incorrect afaics.  Do you have any
> authorative reference?

It is on page 1-18 of the ELF specification version 1.1, at the bottom
of the page.  How unfortunate.  It says:
  In each symbol table, all symbols with STB_LOCAL binding preced the
  weak and global symbols.  As ``Sections'' above describes, a symbol
  table section's sh_info section header member holds the symbol table
  index for the first non-local symbol.
so it is an optimisation, assuming that there are significantly fewer
local than global symbols.


Segher