Re: [PATCH 4/6] x86_64/entry: Mark all syscalls __noendbr

[David Laight <david.laight.linux@gmail.com>]

On Tue, 3 Nov 2026 09:51:43 +0100
Peter Zijlstra <peterz@infradead.org> wrote:

> On Mon, Nov 02, 2026 at 05:06:30PM +0000, David Laight wrote:
> > > --- a/tools/objtool/check.c
> > > +++ b/tools/objtool/check.c
> > > @@ -4672,8 +4672,15 @@ static int validate_ibt(struct objtool_f
> > >  		    !strcmp(sec->name, "__patchable_function_entries"))
> > >  			continue;
> > >  
> > > -		for_each_reloc(sec->rsec, reloc)
> > > +		for_each_reloc(sec->rsec, reloc) {
> > > +			struct symbol *sym = find_symbol_containing(reloc->sec->base,
> > > +								    reloc_offset(reloc));
> > > +
> > > +			if (sym && !strcmp(sym->name, "sys_call_table"))
> > > +				continue;  
> > 
> > Does that slow things down somewhat?
> > Could you do it the other way around??
> > So remember the bounds of sys_call_table and just check whether the relocation
> > in inside it.  
> 
> 
> --- a/tools/objtool/check.c
> +++ b/tools/objtool/check.c
> @@ -4676,7 +4676,7 @@ static int validate_ibt(struct objtool_f
>  			struct symbol *sym = find_symbol_containing(reloc->sec->base,
>  								    reloc_offset(reloc));
>  
> -			if (sym && !strcmp(sym->name, "sys_call_table"))
> +			if (sym && sym->syscall)
>  				continue;

I meant save the symbol info for sys_call_table (or maybe all of them?)
and just see in the relocation in in that region.
Seems better than checking all the symbols and then seeing is a specific
one matched.

David

>  
>  			warnings += validate_ibt_data_reloc(file, reloc);
> --- a/tools/objtool/elf.c
> +++ b/tools/objtool/elf.c
> @@ -556,6 +556,9 @@ static int elf_add_symbol(struct elf *el
>  	if (strstarts(sym->name, ".klp.sym"))
>  		sym->klp = 1;
>  
> +	if (!strcmp(sym->name, "sys_call_table"))
> +		sym->syscall = 1;
> +
>  	if (!sym->klp && !is_sec_sym(sym) && strstr(sym->name, ".cold")) {
>  		sym->cold = 1;
>  
> --- a/tools/objtool/include/objtool/elf.h
> +++ b/tools/objtool/include/objtool/elf.h
> @@ -85,7 +85,7 @@ struct symbol {
>  	u8 fentry            : 1;
>  	u8 profiling_func    : 1;
>  	u8 warned	     : 1;
> -	u8 embedded_insn     : 1;
> +	u8 embedded_insn     : 1; //  8
>  	u8 local_label       : 1;
>  	u8 frame_pointer     : 1;
>  	u8 ignore	     : 1;
> @@ -93,11 +93,12 @@ struct symbol {
>  	u8 cold		     : 1;
>  	u8 prefix	     : 1;
>  	u8 debug_checksum    : 1;
> -	u8 changed	     : 1;
> +	u8 changed	     : 1; // 16
>  	u8 included	     : 1;
>  	u8 klp		     : 1;
>  	u8 dont_correlate    : 1;
>  	u8 fake		     : 1;
> +	u8 syscall           : 1;
>  	struct list_head pv_target;
>  	struct reloc *relocs;
>  	struct section *group_sec;