Re: [Xen-devel] [PATCH] xen: convert lto to Kconfig option

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Mon, Dec 05, 2016 at 08:58:20AM -0700, Jan Beulich wrote:
> >>> On 05.12.16 at 16:27, <wei.liu2@xxxxxxxxxx> wrote:
> > On Mon, Dec 05, 2016 at 03:22:30PM +0000, Wei Liu wrote:
> >> On Mon, Dec 05, 2016 at 08:05:35AM -0700, Jan Beulich wrote:
> >> > >>> On 05.12.16 at 15:39, <wei.liu2@xxxxxxxxxx> wrote:
> >> > > Introduce CONFIG_LTO in Kconfig. Since this is the last option to be
> >> > > converted to Kconfig, delete the preceding comment in Rules.mk as well.
> >> > > 
> >> > > Make it depend on BROKEN because it doesn't work at the moment.
> >> > 
> >> > Looks fine except for this one aspect: Is that brokenness with gcc,
> >> > clang, or both? I wouldn't be surprised if it was broken with gcc (in
> >> 
> >> It's going to be both.
> >> 
> >> Its build rune is broken.
> >> 
> >> I got:
> >> 
> >>   head.S:212:0: fatal error: opening dependency file /..d: Permission 
> >> denied
> >> 
> >> That is, this rule
> >> 
> >>   CFLAGS-y += -MMD -MF $(@D)/.$(@F).d                                      
> >>      
> >   
> >> 
> >> is evaluated too early outside of prerequisite list, which results in
> >> empty string.
> >> 
> > 
> > Sorry, "evaluated too early outside ..." is non-sense. I will just copy
> > the manpage for automatic variables from Make:
> > 
> > "In particular, you cannot use them anywhere within the target list of a
> > rule; they have no value there and will expand to the empty string.
> > Also, they cannot be accessed directly within the prerequisite list of a
> > rule. A common mistake is attempting to use $@ within the prerequisites
> > list; this will not work."
> > 
> > The "empty string" part in my description is accurate though.
> 
> And iirc we've run into the issue (in a less destructive way) before
> (even more than once), and do some filtering of CFLAGS in a few
> places. Apparently we've missed one (or more) ...
> 
> Anyway - feel free to put in the patch with my ack, as it certainly
> doesn't really alter the status quo here.
> 

Thanks!

> Jan
> 

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