On Wed, Jul 26, 2023 at 12:34:15PM +0200, Jan Beulich wrote: > --- a/xen/arch/x86/Kconfig > +++ b/xen/arch/x86/Kconfig > @@ -118,6 +118,36 @@ config HVM > > If unsure, say Y. > > +choice > + prompt "base psABI level" > + default X86_64_BASELINE > + help > + The psABI defines 4 levels of ISA extension sets as a coarse granular > + way of identifying advanced functionality that would be uniformly > + available in respectively newer hardware. While v4 is not really of > + interest for Xen, the others can be selected here, making the > + resulting Xen no longer work on older hardware. This option won't > + have any effect if the toolchain doesn't support the distinction. > + > + If unsure, stick to the default. > + > +config X86_64_BASELINE > + bool "baseline" > + > +config X86_64_V2 > + bool "v2" > + help > + This enables POPCNT and CX16, besides other extensions which are of > + no interest here. > + > +config X86_64_V3 > + bool "v3" > + help > + This enables BMI, BMI2, LZCNT, MOVBE, and XSAVE, besides other > + extensions which are of no interest here. > + > +endchoice > + > config XEN_SHSTK > bool "Supervisor Shadow Stacks" > depends on HAS_AS_CET_SS > --- a/xen/arch/x86/arch.mk > +++ b/xen/arch/x86/arch.mk > @@ -36,6 +36,29 @@ CFLAGS += -mno-red-zone -fpic > # the SSE setup for variadic function calls. > CFLAGS += -mno-mmx -mno-sse $(call cc-option,$(CC),-mskip-rax-setup) > > +# Enable the selected baseline ABI, if supported by the compiler. > +x86-64-$(CONFIG_X86_64_BASELINE) := > +x86-64-$(CONFIG_X86_64_V2) := x86-64-v2 > +x86-64-$(CONFIG_X86_64_V3) := x86-64-v3 > + > +ifneq ($(x86-64-y),) > +CFLAGS-psabi := $(call cc-option,$(CC),-march=$(x86-64-y)) > + > +ifeq ($(CFLAGS-psabi),) > +# Fall back to using the subset of -m... options that are of interest. > +x86-64-v2 := -mpopcnt -mcx16 > +x86-64-v3 := $(x86-64-v2) -mbmi -mbmi2 -mlzcnt -mmovbe -mxsave > +$(call cc-options-add,CFLAGS-psabi,CC,$($(x86-64-y))) > + > +ifneq ($(strip $(CFLAGS-psabi)),$($(x86-64-y))) > +$(warning Options not recognized by $(CC): $(filter-out > $(CFLAGS-psabi),$($(x86-64-y)))) > +XEN_CONFIG_UNSATISFIED += X86_64_Vn
I think I understand Andrew's point on the previous version of this patch. Here, we barely just print a warning if the compiler isn't capable to do what we ask, then do the build and maybe print something after the fact. So we can end up with a build of Xen with an embedded .config which says X86_64_V3 where in fact it's only a build with the baseline ABI. Can't we just fail the build right here instead? I don't see any need to let Kconfig know if the compiler can do x86-64-vX or not, beside only presenting actual available options in `make *config`, and it would override options selected by editing .config directly. > +endif > +endif # CFLAGS-psabi > + > +CFLAGS += $(CFLAGS-psabi) > +endif # x86-64-y Cheers, -- Anthony PERARD
