Re: [Xen-devel] [PATCH v4 2/4] x86/clang: restore integrated assembler usage with indirect thunks

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Feb 19, 2018 at 08:57:15AM -0700, Jan Beulich wrote:
> >>> On 19.02.18 at 15:16, <roger.pau@xxxxxxxxxx> wrote:
> > --- a/xen/arch/x86/Rules.mk
> > +++ b/xen/arch/x86/Rules.mk
> > @@ -44,3 +44,17 @@ endif
> >  
> >  # Set up the assembler include path properly for older toolchains.
> >  CFLAGS += -Wa,-I$(BASEDIR)/include
> > +
> > +ifeq ($(clang),y)
> > +    # Check whether clang asm()-s support .include.
> > +    ifeq ($(call as-insn,$(CC) $(CFLAGS),".include 
> > \"asm/indirect_thunk_asm.h\"",y,n),n)
> 
> Is there anything keeping you from using the slightly less ugly to use
> as-insn-check here? Oh, it's apparently that you want to use CFLAGS,
> not AFLAGS. I wonder whether the other as-insn-check uses wouldn't
> better have CFLAGS passed too. Otherwise please clarify why the
> other construct can't be used by extending the comment.

Right, it's because the .include directive is used with asm()-s in C
files so the parameters for building those use CFLAGS, not AFLAGS.

Also as-insn-check only let's you add to a variable in the success
case, and here I need to do the opposite here.

> > +        CFLAGS += -no-integrated-as
> > +    # Check whether clang keeps .macro-s between asm()-s:
> > +    # https://bugs.llvm.org/show_bug.cgi?id=36110 
> > +    else ifeq ($(if $(shell echo 'void _(void) { asm volatile ( ".macro 
> > FOO\n.endm" ); \
> 
> Careful with this; ./README still says "GNU make 3.80 or later" and
> iirc 3.80 doesn't support "else if..." on a single line.

Hm, OK, I'm afraid I don't have access to make 3.80, but I can
certainly expand this to be

else
    ifeq
    endif
endif

Thanks, Roger.

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