Re: [PATCH v2 03/14] x86/shstk: Introduce Supervisor Shadow Stack support

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Fri, May 29, 2020 at 01:59:55PM +0200, Jan Beulich wrote:
> On 28.05.2020 20:10, Andrew Cooper wrote:
> > On 28/05/2020 11:25, Jan Beulich wrote:
> >> On 27.05.2020 21:18, Andrew Cooper wrote:
> >>> --- a/xen/scripts/Kconfig.include
> >>> +++ b/xen/scripts/Kconfig.include
> >>> @@ -31,6 +31,10 @@ cc-option = $(success,$(CC) -Werror $(CLANG_FLAGS) 
> >>> $(1) -E -x c /dev/null -o /de
> >>>  # Return y if the linker supports <flag>, n otherwise
> >>>  ld-option = $(success,$(LD) -v $(1))
> >>>  
> >>> +# $(as-instr,<instr>)
> >>> +# Return y if the assembler supports <instr>, n otherwise
> >>> +as-instr = $(success,printf "%b\n" "$(1)" | $(CC) $(CLANG_FLAGS) -c -x 
> >>> assembler -o /dev/null -)
> >> Is this actually checking the right thing in the clang case?
> > 
> > Appears to work correctly for me.  (Again, its either fine, or need
> > bugfixing anyway for 4.14, and raising with Linux as this is unmodified
> > upstream code like the rest of Kconfig.include).
> 
> This answer made me try it out: On a system with clang 5 and
> binutils 2.32 "incsspd        %eax" translates fine with
> -no-integrated-as but doesn't without. The previously mentioned
> odd use of CLANG_FLAGS, perhaps together with the disconnect
> from where we establish whether to use -no-integrated-as in the
> first place (arch.mk; I have no idea whether the CFLAGS
> determined would be usable by the kconfig invocation, nor how
> to solve the chicken-and-egg problem there if this is meant to
> work that way), may be the reason for this. Cc-ing Anthony once
> again ...

I've just prepare/sent a patch which should fix this CLANG_FLAGS issue
and allows to tests the assembler in Kconfig.

See: [XEN PATCH] xen/build: introduce CLANG_FLAGS for testing other CFLAGS

-- 
Anthony PERARD