From: Arnd Bergmann <arnd@xxxxxxxx> 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 or a more recent level, add three separate options for v1, v2 and v3 of the architecture as defined by gcc and clang and make them all turn on CONFIG_GENERIC_CPU. Based on this it should be possible to change runtime feature detection into build-time detection for things like cmpxchg16b, or possibly gate features that are only available on older architectures. Link: https://lists.llvm.org/pipermail/llvm-dev/2020-July/143289.html Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx> --- arch/x86/Kconfig.cpu | 39 ++++++++++++++++++++++++++++++++++----- arch/x86/Makefile | 6 ++++++ 2 files changed, 40 insertions(+), 5 deletions(-) diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu index 139db904e564..1461a739237b 100644 --- a/arch/x86/Kconfig.cpu +++ b/arch/x86/Kconfig.cpu @@ -260,7 +260,7 @@ endchoice choice prompt "x86-64 Processor family" depends on X86_64 - default GENERIC_CPU + default X86_64_V2 help This is the processor type of your CPU. This information is used for optimizing purposes. In order to compile a kernel @@ -314,15 +314,44 @@ config MSILVERMONT early Atom CPUs based on the Bonnell microarchitecture, such as Atom 230/330, D4xx/D5xx, D2xxx, N2xxx or Z2xxx. -config GENERIC_CPU - bool "Generic-x86-64" +config X86_64_V1 + bool "Generic x86-64" depends on X86_64 help - Generic x86-64 CPU. - Run equally well on all x86-64 CPUs. + Generic x86-64-v1 CPU. + Run equally well on all x86-64 CPUs, including early Pentium-4 + variants lacking the sahf and cmpxchg16b instructions as well + as the AMD K8 and Intel Core 2 lacking popcnt. + +config X86_64_V2 + bool "Generic x86-64 v2" + depends on X86_64 + help + Generic x86-64-v2 CPU. + Run equally well on all x86-64 CPUs that meet the x86-64-v2 + definition as well as those that only miss the optional + SSE3/SSSE3/SSE4.1 portions. + Examples of this include Intel Nehalem and Silvermont, + AMD Bulldozer (K10) and Jaguar as well as VIA Nano that + include popcnt, cmpxchg16b and sahf. + +config X86_64_V3 + bool "Generic x86-64 v3" + depends on X86_64 + help + Generic x86-64-v3 CPU. + Run equally well on all x86-64 CPUs that meet the x86-64-v3 + definition as well as those that only miss the optional + AVX/AVX2 portions. + Examples of this include the Intel Haswell and AMD Excavator + microarchitectures that include the bmi1/bmi2, lzncnt, movbe + and xsave instruction set extensions. endchoice +config GENERIC_CPU + def_bool X86_64_V1 || X86_64_V2 || X86_64_V3 + config X86_GENERIC bool "Generic x86 support" depends on X86_32 diff --git a/arch/x86/Makefile b/arch/x86/Makefile index 05887ae282f5..1fdc3fc6a54e 100644 --- a/arch/x86/Makefile +++ b/arch/x86/Makefile @@ -183,6 +183,9 @@ else cflags-$(CONFIG_MPSC) += -march=nocona cflags-$(CONFIG_MCORE2) += -march=core2 cflags-$(CONFIG_MSILVERMONT) += -march=silvermont + cflags-$(CONFIG_MX86_64_V1) += -march=x86-64 + cflags-$(CONFIG_MX86_64_V2) += $(call cc-option,-march=x86-64-v2,-march=x86-64) + cflags-$(CONFIG_MX86_64_V3) += $(call cc-option,-march=x86-64-v3,-march=x86-64) cflags-$(CONFIG_GENERIC_CPU) += -mtune=generic KBUILD_CFLAGS += $(cflags-y) @@ -190,6 +193,9 @@ else rustflags-$(CONFIG_MPSC) += -Ctarget-cpu=nocona rustflags-$(CONFIG_MCORE2) += -Ctarget-cpu=core2 rustflags-$(CONFIG_MSILVERMONT) += -Ctarget-cpu=silvermont + rustflags-$(CONFIG_MX86_64_V1) += -Ctarget-cpu=x86-64 + rustflags-$(CONFIG_MX86_64_V2) += -Ctarget-cpu=x86-64-v2 + rustflags-$(CONFIG_MX86_64_V3) += -Ctarget-cpu=x86-64-v3 rustflags-$(CONFIG_GENERIC_CPU) += -Ztune-cpu=generic KBUILD_RUSTFLAGS += $(rustflags-y) -- 2.39.5
