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| author | Arnd Bergmann <arnd@arndb.de> | 2025-02-27 00:37:07 +0300 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2025-02-27 13:19:05 +0300 |
| commit | fc2d5cbe541032e74a66599ba843803cebbfed0e (patch) | |
| tree | 3fc22577c4787836d888b60b9d4b84787d1fb878 | |
| parent | 0abf508675c0dbbca6a387842f90db60756c4af5 (diff) | |
| download | linux-fc2d5cbe541032e74a66599ba843803cebbfed0e.tar.xz | |
x86/build: Rework CONFIG_GENERIC_CPU compiler flags
Building an x86-64 kernel with CONFIG_GENERIC_CPU is documented to
run on all CPUs, but the Makefile does not actually pass an -march=
argument, instead relying on the default that was used to configure
the toolchain.
In many cases, gcc will be configured to -march=x86-64 or -march=k8
for maximum compatibility, but in other cases a distribution default
may be either raised to a more recent ISA, or set to -march=native
to build for the CPU used for compilation. This still works in the
case of building a custom kernel for the local machine.
The point where it breaks down is building a kernel for another
machine that is older the the default target. Changing the default
to -march=x86-64 would make it work reliable, but possibly produce
worse code on distros that intentionally default to a newer ISA.
To allow reliably building a kernel for either the oldest x86-64
CPUs, pass the -march=x86-64 flag to the compiler. This was not
possible in early versions of x86-64 gcc, but works on all currently
supported versions down to at least gcc-5.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20250226213714.4040853-4-arnd@kernel.org
| -rw-r--r-- | arch/x86/Makefile | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 5b773b34768d..5af3172fd51c 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -183,14 +183,14 @@ else cflags-$(CONFIG_MPSC) += -march=nocona cflags-$(CONFIG_MCORE2) += -march=core2 cflags-$(CONFIG_MATOM) += -march=atom - cflags-$(CONFIG_GENERIC_CPU) += -mtune=generic + cflags-$(CONFIG_GENERIC_CPU) += -march=x86-64 -mtune=generic KBUILD_CFLAGS += $(cflags-y) rustflags-$(CONFIG_MK8) += -Ctarget-cpu=k8 rustflags-$(CONFIG_MPSC) += -Ctarget-cpu=nocona rustflags-$(CONFIG_MCORE2) += -Ctarget-cpu=core2 rustflags-$(CONFIG_MATOM) += -Ctarget-cpu=atom - rustflags-$(CONFIG_GENERIC_CPU) += -Ztune-cpu=generic + rustflags-$(CONFIG_GENERIC_CPU) += -Ctarget-cpu=x86-64 -Ztune-cpu=generic KBUILD_RUSTFLAGS += $(rustflags-y) KBUILD_CFLAGS += -mno-red-zone |