linux-kernel - [PATCH 5/5] kbuild: uapi: drop dependency on CC_CAN

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Message-Id: <20251223-uapi-nostdinc-v1-5-d91545d794f7@linutronix.de>
Date: Tue, 23 Dec 2025 08:04:12 +0100
From: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
To: Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nsc@...nel.org>, 
 Brian Cain <bcain@...nel.org>
Cc: linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, 
 bpf@...r.kernel.org, linux-hexagon@...r.kernel.org, 
 Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Subject: [PATCH 5/5] kbuild: uapi: drop dependency on CC_CAN_LINK

The header tests try to compile each header. Some UAPI headers depend on
libc headers so they need a full userspace toolchain to build. This
dependency is expressed in kconfig as a dependency on CC_CAN_LINK.
Many kernel builds do not satisfy CC_CAN_LINK as they only use a
minimal kernel (cross-) compiler. In those configurations the UAPI
headers are not tested at all.

However most UAPI headers do not even depend on any libc headers,
and such dependencies are undesired in any case. Also the static
analysis performed by headers_check.pl does not need CC_CAN_LINK.

Drop the hard dependency on CC_CAN_LINK and instead skip the affected
compilation step for exactly those headers which require libc.

Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
---
 init/Kconfig         | 2 +-
 usr/include/Makefile | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/init/Kconfig b/init/Kconfig
index fa79feb8fe57..4e7ae65683ee 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -247,7 +247,7 @@ config WERROR

 config UAPI_HEADER_TEST
 	bool "Compile test UAPI headers"
-	depends on HEADERS_INSTALL && CC_CAN_LINK
+	depends on HEADERS_INSTALL
 	help
 	  Compile test headers exported to user-space to ensure they are
 	  self-contained, i.e. compilable as standalone units.
diff --git a/usr/include/Makefile b/usr/include/Makefile
index fa01bcda21f5..6d86a53c6f0a 100644
--- a/usr/include/Makefile
+++ b/usr/include/Makefile
@@ -151,7 +151,8 @@ endif
 always-y := $(patsubst $(obj)/%.h,%.hdrtest, $(shell find $(obj) -name '*.h' 2>/dev/null))

 target-no-libc = $(filter-out $(uses-libc), $*.h)
-target-can-compile = $(filter-out $(no-header-test), $*.h)
+target-can-compile = $(and $(filter-out $(no-header-test), $*.h), \
+                           $(or $(CONFIG_CC_CAN_LINK), $(target-no-libc)))

 # Include the header twice to detect missing include guard.
 quiet_cmd_hdrtest = HDRTEST $<

-- 
2.52.0