Re: [PATCH 5.18 13/70] objtool: skip non-text sections when adding return-thunk sites

Greg Kroah-Hartman
2022-07-25T08:37:19Z

On Mon, Jul 25, 2022 at 07:44:08AM +0200, Jiri Slaby wrote:
> Hi,
>
> I wonder, why this is needed in stable and not mainline?
>
> Isn't this a different (non-upstream) dup of
> 951ddecf4356 objtool: Treat .text.__x86.* as noinstr
> ? (That is included in this release too.)
>
> On 22. 07. 22, 11:07, Greg Kroah-Hartman wrote:
> > From: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
> >
> > The .discard.text section is added in order to reserve BRK, with a
> > temporary function just so it can give it a size. This adds a relocation to
> > the return thunk, which objtool will add to the .return_sites section.
> > Linking will then fail as there are references to the .discard.text
> > section.
> >
> > Do not add instructions from non-text sections to the list of return thunk
> > calls, avoiding the reference to .discard.text.
> >
> > Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
> > Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > ---
> > tools/objtool/check.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > --- a/tools/objtool/check.c
> > +++ b/tools/objtool/check.c
> > @@ -1308,7 +1308,9 @@ static void add_return_call(struct objto
> > insn->type = INSN_RETURN;
> > insn->retpoline_safe = true;
> > - list_add_tail(&insn->call_node, &file->return_thunk_list);
> > + /* Skip the non-text sections, specially .discard ones */
> > + if (insn->sec->text)
> > + list_add_tail(&insn->call_node, &file->return_thunk_list);
> > }
> > static bool same_function(struct instruction *insn1, struct instruction *insn2)
> >
> >

I'll let Thadeu reply here, as he did this backport series.

thanks,

greg k-h