On Tue, Jun 23, 2020 at 11:47 AM Borislav Petkov <b...@alien8.de> wrote: > > 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.
Yeah, IIRC, this was fixed in GCC 7.1. See also c868868f6b6a5272350781f9a19b3a5ba1c00b02 00db297106e81770e7c4319014a67896053b5a22 (this one for details about GCC 7.1) e8a170ff9a3576730e43c0dbdd27b7cd3dc56848 > > 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. You already have a conditional below for CC_IS_GCC; just add an else and unconditionally add -msse2. You *should* use -msse2 for GCC 7.1+ IMO. Note that Clang has -mstack-alignment=8 whereas GCC has -mpreferred-stack-boundary=3. (Clang is a value in bytes, GCC is 2^X bytes) I recommend a version check for GCC < 7.1, or simply disabling the self test if the version of GCC used is older than 7.1. Mixing stack alignments is a recipe for GPF with SSE when the caller has a smaller stack alignment than the callee and is also unspecified behavior. It might work today, but as soon as someone perturbs the stack of the call chain, you'll likely see a GPF due to non-16B aligned stack when using SSE with stack operands in the caller. > > 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). ^ looks familiar ;) > # 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 -- Thanks, ~Nick Desaulniers
