Re: Ping: [PATCH] symbols: discard stray file symbols

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

On 9/25/25 9:36 AM, Jan Beulich wrote:

> On 16.04.2025 11:00, Jan Beulich wrote:
> > By observation GNU ld 2.25 may emit file symbols for .data.read_mostly
> > when linking xen.efi. Due to the nature of file symbols in COFF symbol
> > tables (see the code comment) the symbols_offsets[] entries for such
> > symbols would cause assembler warnings regarding value truncation. Of
> > course the resulting entries would also be both meaningless and useless.
> > Add a heuristic to get rid of them, really taking effect only when
> > --all-symbols is specified (otherwise these symbols are discarded
> > anyway).
> >
> > Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> >       
> May I please ask for feedback here, so that hopefully we can have this
> sorted in 4.21?
>     
It is okay for me to have this change in 4.21:
 Release-Acked-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>

~ Oleksii
> Jan
>
> > ---
> > Factor 2 may in principle still be too small: We zap what looks like
> > real file symbols already in read_symbol(), so table_cnt doesn't really
> > reflect the number of symbol table entries encountered. It has proven to
> > work for me in practice though, with still some leeway left.
> >
> > --- a/xen/tools/symbols.c
> > +++ b/xen/tools/symbols.c
> > @@ -213,6 +213,16 @@ static int symbol_valid(struct sym_entry
> >  	if (strstr((char *)s->sym + offset, "_compiled."))
> >  		return 0;
> >  
> > +	/* At least GNU ld 2.25 may emit bogus file symbols referencing a
> > +	 * section name while linking xen.efi. In COFF symbol tables the
> > +	 * "value" of file symbols is a link (symbol table index) to the next
> > +	 * file symbol. Since file (and other) symbols (can) come with one
> > +	 * (or in principle more) auxiliary symbol table entries, the value in
> > +	 * this heuristic is bounded to twice the number of symbols we have
> > +	 * found. See also read_symbol() as to the '?' checked for here. */
> > +	if (s->sym[0] == '?' && s->sym[1] == '.' && s->addr < table_cnt * 2)
> > +		return 0;
> > +
> >  	return 1;
> >  }
> >  
> >       
>