linux-kernel - [PATCH] x86/kbuild/64: Restrict clang versions that can use '-march=native'

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Message-Id: <20250324-x86-march-native-clang-19-and-newer-v1-1-3a05ed32a89e@kernel.org>
Date: Mon, 24 Mar 2025 20:23:00 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Ingo Molnar <mingo@...hat.com>
Cc: x86@...nel.org, Tor Vic <torvic9@...lbox.org>, 
 linux-kernel@...r.kernel.org, llvm@...ts.linux.dev, 
 Nathan Chancellor <nathan@...nel.org>
Subject: [PATCH] x86/kbuild/64: Restrict clang versions that can use
 '-march=native'

There are two issues that can appear when building with clang and
'-march=native'.

The first issue is a compiler crash in the ipv6 stack with clang-18,
such as when building allmodconfig. This was frequently reported on the
LLVM issue tracker [1].

  Stack dump:
  0.      Program arguments: clang ... -march=native ... net/ipv6/ip6_input.c
  1.      <eof> parser at end of file
  2.      Code generation
  3.      Running pass 'Function Pass Manager' on module 'net/ipv6/ip6_input.c'.
  4.      Running pass 'X86 DAG->DAG Instruction Selection' on function '@..._rcv_core'

The second issue is certain -Wframe-larger-than warnings that appear
with clang versions prior to 19, which introduced an optimization that
produces much better code [2].

clang-18:

  drivers/media/pci/saa7164/saa7164-core.c:605:20: error: stack frame size (2392) exceeds limit (2048) in 'saa7164_irq' [-Werror,-Wframe-larger-than]
    605 | static irqreturn_t saa7164_irq(int irq, void *dev_id)
        |                    ^

clang-19:

  drivers/media/pci/saa7164/saa7164-core.c:605:20: error: stack frame size (216) exceeds limit (128) in 'saa7164_irq' [-Werror,-Wframe-larger-than]
    605 | static irqreturn_t saa7164_irq(int irq, void *dev_id)
        |                    ^

Restrict the testing of the availability of '-march=native' to all
supported GCC versions and clang-19 and newer to avoid these known
resolved issues.

Fixes: 0480bc7e65dc ("x86/kbuild/64: Add the CONFIG_X86_NATIVE_CPU option to locally optimize the kernel with '-march=native'")
Link: https://github.com/llvm/llvm-project/issues?q=is%3Aissue%20ip6_rcv_core [1]
Link: https://github.com/llvm/llvm-project/commit/90ba33099cbb17e7c159e9ebc5a512037db99d6d [2]
Signed-off-by: Nathan Chancellor <nathan@...nel.org>
---
 arch/x86/Kconfig.cpu | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu
index 87bede96e800..f928cf6e3252 100644
--- a/arch/x86/Kconfig.cpu
+++ b/arch/x86/Kconfig.cpu
@@ -248,6 +248,12 @@ endchoice
 config CC_HAS_MARCH_NATIVE
 	# This flag might not be available in cross-compilers:
 	def_bool $(cc-option, -march=native)
+	# LLVM 18 has an easily triggered internal compiler error in core
+	# networking code with '-march=native' on certain systems:
+	# https://github.com/llvm/llvm-project/issues/72026
+	# LLVM 19 introduces an optimization that resolves some high stack
+	# usage warnings that only appear wth '-march=native'.
+	depends on CC_IS_GCC || CLANG_VERSION >= 190100
 
 config X86_NATIVE_CPU
 	bool "Build and optimize for local/native CPU"

---
base-commit: 7c241e07bddf9300af40c0dd44367a83df633f35
change-id: 20250324-x86-march-native-clang-19-and-newer-2425d8524eb9

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