From: Nathan Chancellor Date: Tue, 25 Mar 2025 03:23:00 +0000 (-0700) Subject: x86/kbuild/64: Restrict clang versions that can use '-march=native' X-Git-Tag: v6.16-rc1~191^2 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ad9b861824ac55d81431815fffaaff5e981badc1;p=thirdparty%2Fkernel%2Flinux.git 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: # Link: https://github.com/llvm/llvm-project/issues?q=is%3Aissue%20ip6_rcv_core Stack dump: 0. Program arguments: clang ... -march=native ... net/ipv6/ip6_input.c 1. 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: # Link: https://github.com/llvm/llvm-project/commit/90ba33099cbb17e7c159e9ebc5a512037db99d6d [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'") Signed-off-by: Nathan Chancellor Signed-off-by: Ingo Molnar Cc: Nick Desaulniers Cc: Tor Vic Cc: Andy Lutomirski Cc: Brian Gerst Cc: Juergen Gross Cc: H. Peter Anvin Cc: Kees Cook Cc: Josh Poimboeuf Cc: Linus Torvalds Link: https://lore.kernel.org/r/20250324-x86-march-native-clang-19-and-newer-v1-1-3a05ed32a89e@kernel.org --- diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu index 87bede96e8009..f928cf6e32524 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"