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SubjectRe: [PATCH 2/2] selftests/fpu: Add an FPU selftest
On Tue, Jun 23, 2020 at 11:22:53AM -0700, Andy Lutomirski wrote:
> See that same atrocious bug report. It's the insane interaction
> between -mno-sse2 and -mpreferred-stack-boundary. So you need to
> cc-option them both? Or just stick with a compiler version check, I
> guess.

Yes, it was the interaction. This below seems to work. Note the "-msse"
in the first argument of cc-option which causes the compiler to error
out with

/dev/null:1:0: error: -mpreferred-stack-boundary=3 is not between 4 and 12

Adding Nick for the clang side.

@Nick: I'm simply going to add -msse2 with cc-option.

Anyway, lemme test this thing a bit more.

Thx.

---

# CFLAGS for compiling floating point code inside the kernel. x86/Makefile turns
# off the generation of FPU/SSE* instructions for kernel proper but FPU_FLAGS
# get appended last to CFLAGS and thus override those previous compiler options.
#
FPU_CFLAGS := -mhard-float -msse
FPU_CFLAGS += $(call cc-option,-msse2,)
ifdef CONFIG_CC_IS_GCC
# Stack alignment mismatch, proceed with caution.
# GCC < 7.1 cannot compile code using `double` and -mpreferred-stack-boundary=3
# (8B stack alignment).
# See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53383
FPU_CFLAGS += $(call cc-option,-msse -mpreferred-stack-boundary=3,-mpreferred-stack-boundary=4)
endif

obj-$(CONFIG_TEST_FPU) += test_fpu.o
CFLAGS_test_fpu.o += $(FPU_CFLAGS)

--
Regards/Gruss,
Boris.

https://people.kernel.org/tglx/notes-about-netiquette

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