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

[sashiko-bot@kernel.org]

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 <jpoimboe@kernel.org>

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.

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/cover.1785727106.git.jpoimboe@kernel.org?part=5