Re: The trouble with __weak and objtool got worse

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

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:
> > [ huge snip ]
> > 
> > > This seems to happen when objtool cannot find a section symbol, in which
> > > case it falls back to any other symbol to key off of, however in this
> > > case that goes terribly wrong!
> > 
> > That is an objtool problem then.  Fix objtool so it looks at symbols
> > directly?
> 
> I'm not sure what you're saying.

So sorry.  "So that it looks at *sections* directly", I meant to say.

> > > 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?

> I ran into that when I violated that contraint at some point and
> the various elf tools screamed at me.

Huh.  Can you show anything that reproduces that?


Segher