linux-kernel - [PATCH v4 06/17] kbuild: add stamp file for vmlinux BTF data

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Message-Id: <20260113-module-hashes-v4-6-0b932db9b56b@weissschuh.net>
Date: Tue, 13 Jan 2026 13:28:50 +0100
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Nathan Chancellor <nathan@...nel.org>, Arnd Bergmann <arnd@...db.de>, 
 Luis Chamberlain <mcgrof@...nel.org>, Petr Pavlu <petr.pavlu@...e.com>, 
 Sami Tolvanen <samitolvanen@...gle.com>, 
 Daniel Gomez <da.gomez@...sung.com>, Paul Moore <paul@...l-moore.com>, 
 James Morris <jmorris@...ei.org>, "Serge E. Hallyn" <serge@...lyn.com>, 
 Jonathan Corbet <corbet@....net>, Madhavan Srinivasan <maddy@...ux.ibm.com>, 
 Michael Ellerman <mpe@...erman.id.au>, Nicholas Piggin <npiggin@...il.com>, 
 Naveen N Rao <naveen@...nel.org>, Mimi Zohar <zohar@...ux.ibm.com>, 
 Roberto Sassu <roberto.sassu@...wei.com>, 
 Dmitry Kasatkin <dmitry.kasatkin@...il.com>, 
 Eric Snowberg <eric.snowberg@...cle.com>, 
 Nicolas Schier <nicolas.schier@...ux.dev>, 
 Daniel Gomez <da.gomez@...nel.org>, Aaron Tomlin <atomlin@...mlin.com>, 
 "Christophe Leroy (CS GROUP)" <chleroy@...nel.org>, 
 Nicolas Schier <nsc@...nel.org>, 
 Nicolas Bouchinet <nicolas.bouchinet@....cyber.gouv.fr>, 
 Xiu Jianfeng <xiujianfeng@...wei.com>, Nicolas Schier <nsc@...nel.org>, 
 Christophe Leroy <chleroy@...nel.org>
Cc: Fabian Grünbichler <f.gruenbichler@...xmox.com>, 
 Arnout Engelen <arnout@...t.net>, Mattia Rizzolo <mattia@...reri.org>, 
 kpcyrd <kpcyrd@...hlinux.org>, Christian Heusel <christian@...sel.eu>, 
 Câju Mihai-Drosi <mcaju95@...il.com>, 
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>, 
 linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-arch@...r.kernel.org, linux-modules@...r.kernel.org, 
 linux-security-module@...r.kernel.org, linux-doc@...r.kernel.org, 
 linuxppc-dev@...ts.ozlabs.org, linux-integrity@...r.kernel.org, 
 Thomas Weißschuh <linux@...ssschuh.net>
Subject: [PATCH v4 06/17] kbuild: add stamp file for vmlinux BTF data

The upcoming module hashes functionality will build the modules in
between the generation of the BTF data and the final link of vmlinux.
Having a dependency from the modules on vmlinux would make this
impossible as it would mean having a cyclic dependency.
Break this cyclic dependency by introducing a new target.

Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
---
 scripts/Makefile.modfinal | 4 ++--
 scripts/link-vmlinux.sh   | 6 ++++++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/scripts/Makefile.modfinal b/scripts/Makefile.modfinal
index 149e12ff5700..adfef1e002a9 100644
--- a/scripts/Makefile.modfinal
+++ b/scripts/Makefile.modfinal
@@ -56,8 +56,8 @@ if_changed_except = $(if $(call newer_prereqs_except,$(2))$(cmd-check),      \
 	printf '%s\n' 'savedcmd_$@ := $(make-cmd)' > $(dot-target).cmd, @:)

 # Re-generate module BTFs if either module's .ko or vmlinux changed
-%.ko: %.o %.mod.o .module-common.o $(objtree)/scripts/module.lds $(and $(CONFIG_DEBUG_INFO_BTF_MODULES),$(KBUILD_BUILTIN),$(objtree)/vmlinux) FORCE
-	+$(call if_changed_except,ld_ko_o,$(objtree)/vmlinux)
+%.ko: %.o %.mod.o .module-common.o $(objtree)/scripts/module.lds $(and $(CONFIG_DEBUG_INFO_BTF_MODULES),$(KBUILD_BUILTIN),$(objtree)/.tmp_vmlinux_btf.stamp) FORCE
+	+$(call if_changed_except,ld_ko_o,$(objtree)/.tmp_vmlinux_btf.stamp)
 ifdef CONFIG_DEBUG_INFO_BTF_MODULES
 	+$(if $(newer-prereqs),$(call cmd,btf_ko))
 endif
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 4ab44c73da4d..8c98f8645a5c 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -111,6 +111,7 @@ vmlinux_link()
 gen_btf()
 {
 	local btf_data=${1}.btf.o
+	local btf_stamp=.tmp_vmlinux_btf.stamp

 	info BTF "${btf_data}"
 	LLVM_OBJCOPY="${OBJCOPY}" ${PAHOLE} -J ${PAHOLE_FLAGS} ${1}
@@ -131,6 +132,11 @@ gen_btf()
 	fi
 	printf "${et_rel}" | dd of="${btf_data}" conv=notrunc bs=1 seek=16 status=none

+	info STAMP $btf_stamp
+	if ! cmp --silent $btf_data $btf_stamp; then
+		cp $btf_data $btf_stamp
+	fi
+
 	btf_vmlinux_bin_o=${btf_data}
 }

-- 
2.52.0