Re: [PATCH 05/14] objtool/klp: Add .klp.symid for sympos disambiguation
From: Josh Poimboeuf <jpoimboe@kernel.org>
Date: 2026-08-12 20:22:55
Also in:
live-patching
On Wed, Aug 12, 2026 at 02:13:00PM +0100, Puranjay Mohan wrote:
Applying the patch below fixes it:
-- >8 --
From 93c99313870d7375ab07e494c2d0d971758578eb Mon Sep 17 00:00:00 2001
From: Puranjay Mohan <puranjay@kernel.org>
Date: Fri, 7 Aug 2026 11:16:29 -0700
Subject: [PATCH] objtool/klp: Fix vmlinux .klp.symid link error for
.exitcall.exit symbols
Building a kernel via klp-build fails to link:
`__exitcall_aes_mod_exit' referenced in section `.klp.symid' of vmlinux.o: defined in discarded section `.exitcall.exit' of vmlinux.o
`__exitcall_dax_exit' referenced in section `.klp.symid' of vmlinux.o: defined in discarded section `.exitcall.exit' of vmlinux.o
`__exitcall_hid_exit' referenced in section `.klp.symid' of vmlinux.o: defined in discarded section `.exitcall.exit' of vmlinux.o
`__exitcall_usb_serial_module_exit' referenced in section `.klp.symid' of vmlinux.o: defined in discarded section `.exitcall.exit' of vmlinux.o
module_exit() on a built-in emits a static __exitcall_$fn pointer into
.exitcall.exit, which vmlinux.lds.h discards unconditionally via
EXIT_CALL. When two built-in translation units define a module_exit()
function of the same name, the resulting local symbols collide,
symid_needed() sees a duplicate and emits a .klp.symid entry for each,
referencing symbols the linker then throws away.
Same-named module_exit() functions are not rare:
dax_exit drivers/dax/device.c, drivers/dax/fsdev.c
hid_exit drivers/hid/hid-core.c, drivers/hid/usbhid/hid-core.c
aes_mod_exit arch/arm64/crypto/aes-ce-ccm-glue.c, lib/crypto/aes.c
usb_serial_module_exit module_usb_serial_driver() expands to this fixed
name in each of its ~49 users
The last one makes the collision structural rather than accidental: any
kernel with two built-in USB serial drivers has it. This is not arch
specific either; it only requires the objects to be built in rather than
modular, which is why a monolithic config trips it while a typical
distro config does not.
Add .exitcall.exit to the discarded section list so its symbols don't get
symids.
This is the same failure mode as "objtool/klp: Fix vmlinux .klp.symid
link error for .no_trim_symbol symbols", for another unconditionally
discarded allocated section.
Fixes: 029223d30162 ("objtool/klp: Add .klp.symid for sympos disambiguation")
Signed-off-by: Puranjay Mohan <puranjay@kernel.org>Indeed, I'll add it to the queue, thanks! -- Josh