Re: [PATCH v3 14/21] objtool: Prevent kCFI hashes from being decoded as instructions

On Fri, May 15, 2026 at 12:16:51AM +0000, [email protected] wrote:
> Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
> - [High] Build failure due to undeclared mapping symbol functions.
> - [Low] Unused header inclusion.
> --
> 
> commit 4ad78a24a64cd6a2d10b9a2f9c0d306fba3e6d19
> Author: Josh Poimboeuf <[email protected]>
> 
> objtool: Prevent kCFI hashes from being decoded as instructions
> 
> On arm64 with CONFIG_CFI=y, Clang places a 4-byte kCFI type hash immediately
> before each address-taken function entry. This commit uses mapping symbols
> to mark such data as NOP in text sections to prevent objtool from decoding
> them.
> 
> > diff --git a/tools/objtool/check.c b/tools/objtool/check.c
> > index e05dc7a93dc1e..2b03a2d6fc952 100644
> > --- a/tools/objtool/check.c
> > +++ b/tools/objtool/check.c
> > @@ -25,6 +25,7 @@
> >  #include <linux/kernel.h>
> >  #include <linux/static_call_types.h>
> >  #include <linux/string.h>
> > +#include <linux/kconfig.h>
> 
> This isn't a bug, but is this include needed? It doesn't appear that any
> Kconfig configuration macros are being used in the modified code.

Fixed.

> 
> [ ... ]
> 
> > @@ -478,6 +483,16 @@ static int decode_instructions(struct objtool_file *file)
> >  
> >  			prev_len = insn->len;
> >  
> > +			/* Use mapping symbols to skip data in text sections */
> > +			sec_for_each_sym_from(sec, map_sym) {
> > +				if (map_sym->offset > offset)
> > +					break;
> > +				if (is_mapping_sym(map_sym))
> > +					is_data = is_data_mapping_sym(map_sym);
> 
> Could this cause a build failure across architectures here? It appears
> is_mapping_sym() and is_data_mapping_sym() are neither declared nor defined
> anywhere in the codebase at this point in the patch series.
> 
> If these functions are only introduced in a subsequent commit, applying
> this patch independently might result in an implicit declaration of function
> error, breaking git bisectability.

Fixes.

-- 
Josh