[PATCH v2] kbuild: Reject unexpected values for LLVM=

[Thomas Weißschuh]

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@xxxxxxxxxxxxxx>
---
Changes in v2:
- Add pointer to the documentation.
- Link to v1: https://patch.msgid.link/20260112-kbuild-llvm-arg-v1-1-8e9bbdae996f@xxxxxxxxxxxxxx
---
 Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/Makefile b/Makefile
index e404e4767944..4cf187f70171 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, see Documentation/kbuild/llvm.rst)
 endif
 
 HOSTCC	= $(LLVM_PREFIX)clang$(LLVM_SUFFIX)

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

Best regards,
-- 
Thomas Weißschuh <linux@xxxxxxxxxxxxxx>