On 11.08.2023 16:59, Anthony PERARD wrote: > On Wed, Jul 26, 2023 at 12:34:15PM +0200, Jan Beulich wrote: >> --- 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.
Which isn't really a problem, is it? Even if passed the respective option, the compiler may equally choose to use none of the thus available insns. (It won't typically, but it still could.) > Can't we just fail the build right here instead? Whether to do so is not the user's choice (see patch 2). See also both post-commit-message remarks there. > 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. I'm afraid I don't understand what you're suggesting here that I do differently. Jan
