linux-kernel - [PATCH 04/11] ARM: Remove Thumb2 __builtin_thread

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Message-Id: <20240125-bump-min-llvm-ver-to-13-0-1-v1-4-f5ff9bda41c5@kernel.org>
Date: Thu, 25 Jan 2024 15:55:10 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: akpm@...ux-foundation.org, masahiroy@...nel.org
Cc: nicolas@...sle.eu, linux-kbuild@...r.kernel.org, llvm@...ts.linux.dev, 
 patches@...ts.linux.dev, linux-kernel@...r.kernel.org, 
 Nathan Chancellor <nathan@...nel.org>, linux@...linux.org.uk, 
 ardb@...nel.org, linux-arm-kernel@...ts.infradead.org
Subject: [PATCH 04/11] ARM: Remove Thumb2 __builtin_thread_pointer
 workaround for Clang

Now that the minimum supported version of LLVM for building the kernel
has been bumped to 13.0.1, the conditional expression added to
get_current() by commit c1e42efacb9b ("ARM: 9151/1: Thumb2: avoid
__builtin_thread_pointer() on Clang") is always true, as the build will
fail during the configuration stage for older LLVM versions. Remove it,
effectively reverting the aforementioned change.

Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---
Cc: linux@...linux.org.uk
Cc: ardb@...nel.org
Cc: linux-arm-kernel@...ts.infradead.org
---
 arch/arm/include/asm/current.h | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/arch/arm/include/asm/current.h b/arch/arm/include/asm/current.h
index 1e1178bf176d..5225cb1c803b 100644
--- a/arch/arm/include/asm/current.h
+++ b/arch/arm/include/asm/current.h
@@ -18,18 +18,12 @@ static __always_inline __attribute_const__ struct task_struct *get_current(void)
 {
 	struct task_struct *cur;
 
-#if __has_builtin(__builtin_thread_pointer) && \
-    defined(CONFIG_CURRENT_POINTER_IN_TPIDRURO) && \
-    !(defined(CONFIG_THUMB2_KERNEL) && \
-      defined(CONFIG_CC_IS_CLANG) && CONFIG_CLANG_VERSION < 130001)
+#if __has_builtin(__builtin_thread_pointer) && defined(CONFIG_CURRENT_POINTER_IN_TPIDRURO)
 	/*
 	 * Use the __builtin helper when available - this results in better
 	 * code, especially when using GCC in combination with the per-task
 	 * stack protector, as the compiler will recognize that it needs to
 	 * load the TLS register only once in every function.
-	 *
-	 * Clang < 13.0.1 gets this wrong for Thumb2 builds:
-	 * https://github.com/ClangBuiltLinux/linux/issues/1485
 	 */
 	cur = __builtin_thread_pointer();
 #elif defined(CONFIG_CURRENT_POINTER_IN_TPIDRURO) || defined(CONFIG_SMP)

-- 
2.43.0