linux-kernel - [PATCH] compiler-clang.h: Require LLVM 19.1.0 or higher for __typeof_unqual_

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Message-Id: <20260116-require-llvm-19-1-for-typeof_unqual-v1-1-3b9a4a4b212b@kernel.org>
Date: Fri, 16 Jan 2026 16:26:27 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Nick Desaulniers <nick.desaulniers+lkml@...il.com>, 
 Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
 Uros Bizjak <ubizjak@...il.com>, llvm@...ts.linux.dev, 
 linux-kernel@...r.kernel.org, Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH] compiler-clang.h: Require LLVM 19.1.0 or higher for
 __typeof_unqual__

When building the kernel using a version of LLVM between llvmorg-19-init
(the first commit of the LLVM 19 development cycle) and the change in
LLVM that actually added __typeof_unqual__ for all C modes [1], which
might happen during a bisect of LLVM, there is a build failure:

  In file included from arch/x86/kernel/asm-offsets.c:9:
  In file included from include/linux/crypto.h:15:
  In file included from include/linux/completion.h:12:
  In file included from include/linux/swait.h:7:
  In file included from include/linux/spinlock.h:56:
  In file included from include/linux/preempt.h:79:
  arch/x86/include/asm/preempt.h:61:2: error: call to undeclared function '__typeof_unqual__'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
     61 |         raw_cpu_and_4(__preempt_count, ~PREEMPT_NEED_RESCHED);
        |         ^
  arch/x86/include/asm/percpu.h:478:36: note: expanded from macro 'raw_cpu_and_4'
    478 | #define raw_cpu_and_4(pcp, val)                         percpu_binary_op(4, , "and", (pcp), val)
        |                                                         ^
  arch/x86/include/asm/percpu.h:210:3: note: expanded from macro 'percpu_binary_op'
    210 |                 TYPEOF_UNQUAL(_var) pto_tmp__;                          \
        |                 ^
  include/linux/compiler.h:248:29: note: expanded from macro 'TYPEOF_UNQUAL'
    248 | # define TYPEOF_UNQUAL(exp) __typeof_unqual__(exp)
        |                             ^

The current logic of CC_HAS_TYPEOF_UNQUAL just checks for a major
version of 19 but half of the 19 development cycle did not have support
for __typeof_unqual__.

Harden the logic of CC_HAS_TYPEOF_UNQUAL to avoid this error by only
using __typeof_unqual__ with a released version of LLVM 19, which is
greater than or equal to 19.1.0 with LLVM's versioning scheme that
matches GCC's [2].

Link: https://github.com/llvm/llvm-project/commit/cc308f60d41744b5920ec2e2e5b25e1273c8704b [1]
Link: https://github.com/llvm/llvm-project/commit/4532617ae420056bf32f6403dde07fb99d276a49 [2]
Fixes: ac053946f5c4 ("compiler.h: introduce TYPEOF_UNQUAL() macro")
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---
 include/linux/compiler-clang.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/compiler-clang.h b/include/linux/compiler-clang.h
index 107ce05bd16e..cccc72fd336b 100644
--- a/include/linux/compiler-clang.h
+++ b/include/linux/compiler-clang.h
@@ -152,4 +152,4 @@
  * Bindgen uses LLVM even if our C compiler is GCC, so we cannot
  * rely on the auto-detected CONFIG_CC_HAS_TYPEOF_UNQUAL.
  */
-#define CC_HAS_TYPEOF_UNQUAL (__clang_major__ >= 19)
+#define CC_HAS_TYPEOF_UNQUAL (__clang_major__ > 19 || (__clang_major__ == 19 && __clang_minor__ > 0))

---
base-commit: e9a6fb0bcdd7609be6969112f3fbfcce3b1d4a7c
change-id: 20260116-require-llvm-19-1-for-typeof_unqual-5a5ac3e7dfac

Best regards,
--  
Nathan Chancellor <nathan@...nel.org>