Re: [PATCH 05/14] objtool/klp: Add .klp.symid for sympos disambiguation

On Mon, Aug 03, 2026 at 03:41:15AM +0000, [email protected] wrote:
> Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
> - [Low] Relocations in .klp.symid pointing to discarded sections (.exitcall.exit, .exit.text, etc.) will cause a link-time error when building vmlinux.
> --
> 
> --- Patch [5]: [PATCH 05/14] objtool/klp: Add .klp.symid for sympos disambiguation ---
> commit 09454266fcd41f3c022cac215ab86d1269c37d52
> Author: Josh Poimboeuf <[email protected]>
> 
> objtool/klp: Add .klp.symid for sympos disambiguation
> 
> This commit introduces a new .klp.symid section to vmlinux.o to help
> livepatch reliably determine the sympos of duplicate-named symbols. It
> emits an array of identifiers and relocations that survives the final link,
> allowing klp-diff to correlate symbols between vmlinux.o and vmlinux.
> 
> > diff --git a/tools/objtool/klp-symid.c b/tools/objtool/klp-symid.c
> > new file mode 100644
> > index 0000000000000..cf188cdfa6079
> > --- /dev/null
> > +++ b/tools/objtool/klp-symid.c
> [ ... ]
> > +static const char * const discarded_secs[] = {
> > +	".discard",
> > +	".modinfo",
> > +	"__tracepoint_check",
> > +};
> > +
> > +static bool discarded_sec(struct section *sec)
> > +{
> > +	if (!(sec->sh.sh_flags & SHF_ALLOC))
> > +		return true;
> > +
> > +	for (int i = 0; i < ARRAY_SIZE(discarded_secs); i++)
> > +		if (strstarts(sec->name, discarded_secs[i]))
> > +			return true;
> > +
> > +	return false;
> > +}
> 
> [Severity: Low]
> Should the discarded_secs array also include .exitcall.exit and .exit.
> sections?
> 
> Because these exit sections have the SHF_ALLOC flag set, the first check in
> discarded_sec() will not catch them. If they are also omitted from the
> discarded_secs array, klp_create_symid_sections() will mistakenly generate
> relocations pointing to them.
> 
> Since the linker script unconditionally discards .exitcall.exit via the
> DISCARDS macro, generating relocations against it causes a deterministic
> link-time error ("relocation refers to a discarded section") when building
> vmlinux.
> 
> Could this happen in practice? Common driver exit handlers (e.g.,
> module_cleanup used by drivers like cx18 and ivtv) often result in
> duplicate static symbols like __exitcall_module_cleanup in the
> .exitcall.exit section when the modules are built-in.

I'm not convinced this can happen in practice.  Why would somebody be
trying to patch or reference a module exit symbol anyway?

-- 
Josh