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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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.

Jan


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