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

From: Nathan Chancellor
Date: Mon Mar 24 2025 - 23:23:28 EST


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 '@ip6_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@xxxxxxxxxx>
---
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@xxxxxxxxxx>