Re: [XEN PATCH v4 12/18] xen/build: factorise generation of the linker scripts

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

On Wed, Apr 08, 2020 at 02:46:42PM +0200, Jan Beulich wrote:
> On 31.03.2020 12:30, Anthony PERARD wrote:
> >     - avoid using "define" for cmd_cc_lds_S, as adding '; \' on each line is
> >       still mandatory for if_changed (or cmd) macro to work.
> 
> I still don't believe in there being a need for "; \" there. This
> actually breaks things, after all:
> 
> > --- a/xen/Rules.mk
> > +++ b/xen/Rules.mk
> > @@ -236,6 +236,12 @@ cmd_s_S = $(CPP) $(filter-out -Wa$(comma)%,$(a_flags)) 
> > $< -o $@
> >  %.s: %.S FORCE
> >     $(call if_changed,cpp_s_S)
> >  
> > +# Linker scripts, .lds.S -> .lds
> > +quiet_cmd_cc_lds_S = LDS     $@
> > +cmd_cc_lds_S = $(CPP) -P $(filter-out -Wa$(comma)%,$(a_flags)) -o $@ $<; \
> > +    sed -e 's/.*\.lds\.o:/$(@F):/g' <$(dot-target).d >$(dot-target).d.new; 
> > \
> > +    mv -f $(dot-target).d.new $(dot-target).d
> 
> if $(CPP) or sed fail, previously the whole rule would have failed,
> which no longer is the case with your use of semicolons. There
> ought to be a solution to this, ideally one better than adding
> "set -e" as the first command ("define" would at least deal with
> the multi-line make issue, but without it being clear to me why the
> semicolons would be needed I don't think I can suggest anything
> there at the moment).

The only macro that will consumes cmd_cc_lds_S (and other cmd_*) is
"cmd", it is defined as:
    cmd = @set -e; $(echo-cmd) $(cmd_$(1))
So, "set -e" is already there, and using semicolons in commands is
equivalent to using "&&".

With "cmd" alone, multi-line command would work as expected (unless
$(echo-cmd) is is trying to print the command line).

It's "if_changed" macro that doesn't work with multi-line commands.
It does:
    $(cmd); printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd
With a multiple line command, $(make-cmd) get's expanded to multiple
line, so the second argument of "printf" is going to be spread over
multiple line in make, and thus multiple shell. We run into this error:
    /bin/sh: -c: line 0: unexpected EOF while looking for matching `''
    /bin/sh: -c: line 1: syntax error: unexpected end of file

This is why we need to have commands on a single line.

I hope the explanation is clear enough.

Thanks,

-- 
Anthony PERARD