linux-kernel - [PATCH] kbuild: Reject unexpected values for LLVM=

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Message-Id: <20260112-kbuild-llvm-arg-v1-1-8e9bbdae996f@weissschuh.net>
Date: Mon, 12 Jan 2026 07:43:52 +0100
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nsc@...nel.org>, 
 Nick Desaulniers <nick.desaulniers+lkml@...il.com>, 
 Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>
Cc: linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, 
 llvm@...ts.linux.dev, 
 Thomas Weißschuh <linux@...ssschuh.net>
Subject: [PATCH] kbuild: Reject unexpected values for LLVM=

The LLVM argument is documented to accept one of three forms:
* a literal '1' to use the default 'clang',
* a toolchain prefix path, ending in a trailing '/',
* a version suffix.

All other values are silently treated as '1'. If for example
the user accidentally forgets the trailing '/' of a toolchain prefix,
kbuild will unexpectedly and silently fall back to the system toolchain.

Instead report an error if the user specified an invalid value for LLVM.

Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
---
 Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Makefile b/Makefile
index e404e4767944..2a085a1b6875 100644
--- a/Makefile
+++ b/Makefile
@@ -447,6 +447,8 @@ ifneq ($(filter %/,$(LLVM)),)
 LLVM_PREFIX := $(LLVM)
 else ifneq ($(filter -%,$(LLVM)),)
 LLVM_SUFFIX := $(LLVM)
+else ifneq ($(LLVM),1)
+$(error Invalid value for LLVM=)
 endif
 
 HOSTCC	= $(LLVM_PREFIX)clang$(LLVM_SUFFIX)

---
base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
change-id: 20260111-kbuild-llvm-arg-c7346a4f2b3a

Best regards,
-- 
Thomas Weißschuh <linux@...ssschuh.net>