On Mon, Sep 13, 2021 at 04:05:15PM +0200, Jan Beulich wrote:
> On 13.09.2021 15:37, Roger Pau Monné wrote:
> > On Thu, Sep 09, 2021 at 04:35:49PM +0200, Jan Beulich wrote:
> >> I haven't been able to find an environment where I could actually try
> >> with lld (ld.lld); all testing was with GNU ld (ld.bfd).
> >
> > Thanks for fixing this. I've been able to test with LLVM ld and the
> > workaround is fine.
>
> Oh, good, thanks for trying this out.
>
> >> --- a/xen/arch/x86/Makefile
> >> +++ b/xen/arch/x86/Makefile
> >> @@ -92,10 +92,16 @@ efi-$(CONFIG_PV_SHIM_EXCLUSIVE) :=
> >>
> >> ifneq ($(build_id_linker),)
> >> notes_phdrs = --notes
> >> +# Determine whether to engage a workaround for GNU ld 2.37.
> >> +build-id-ld-good = $(shell echo 'void test(void) {}' \
> >> + | $(CC) $(XEN_CFLAGS) -o .check.o -c -x c -
> >> 2>.check.err \
> >> + && $(LD) -T check.lds -o .check.elf .check.o
> >> 2>>.check.err \
> >> + && echo y)
> >
> > Do we want to make this a Kconfig option (ie: LD_UNQUOTED_DASH) and
> > then use is here?
> >
> > We already have compiler and assembler checks in x86/Kconfig, so it
> > would seem more natural to place it there.
>
> The question of whether to record tool chain capabilities in .config
> is still pending. I'm not convinced this is a good idea, Andrew keeps
> shouting me out for that, and an actual discussion doesn't really
> happen. Yet unlike back at the time when I first raised my concern,
> Anthony meanwhile supports me in at least the question (to Andrew) of
> when such a discussion would have happened: Neither of us is aware,
> yet Andrew claims it did happen, but so far didn't point out where
> one could read about what was discussed and decided there.
>
> For the few uses we've accumulated I gave (if at all) an ack for
> things happening under some sort of pressure, with the request that
> aformentioned discussion would happen subsequently (and, depending on
> outcome, these would be converted to another approach if need be). I
> have meanwhile realized that it was a mistake to allow such things in
> on this basis - the more of them we gain, the more I'm hearing "we've
> already got some".
I see, that's not an ideal situation from a review PoV, as we don't
have a clear placement for those and that will just cause confusion
(and more work since there are potentially two places to check).
What's the benefit of placing the checks in Kconfig instead of the
Makefiles?
As I understand Kconfig is run only once, while the Makefile could run
the check multiple times.
The downfall of having them in .config is that .config could suddenly
change as tools are updated or as it's moved around different systems
(yet .config already contains specific compiler version information).
> >> else
> >> ifeq ($(CONFIG_PVH_GUEST),y)
> >> notes_phdrs = --notes
> >> endif
> >> +build-id-ld-good := y
> >> endif
> >
> > I also wonder whether we need to make the quoting tied to the usage of
> > build-id. I guess we don't add sections with dashes and instead
> > use underscores, but it might be prudent to always quote to be on the
> > safe side if dashes are not supported.
>
> If quoting was uniformly supported, I might have considered that. But
> it not being uniformly supported is the reason for this change in the
> first place. Hence I'd prefer to generalize this only if really needed.
OK, FE. As said I don't we would deliberately add sections with
slashes.
> >> --- /dev/null
> >> +++ b/xen/arch/x86/check.lds
> >
> > I would maybe name this check-dash.lds, in case we need to add more ld
> > build tests.
>
> I sincerely hope it was a one-off that a binutils release got cut with
> this sort of a supposedly prominent bug. Considering that the dash is
> merely what we're after in this specific case, but breakage was wider
> (presumably about any printable char that's not alnum or underscore),
> I'd consider check-dash too specific a name. You only say "maybe"; if
> you were sufficiently convinced, this is an adjustment I'd be willing
> to make. Yet even better would be if I / we could just be done with
> this.
Ack, we can always rename at a later point if there's a need to,
hopefully we are not being too optimistic.
Thanks, Roger.
