Re: [Xen-devel] [PATCH] x86emul/test: disable pie for 64-bit builds

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 25.09.17 at 13:43, <wei.liu2@xxxxxxxxxx> wrote:
> On Mon, Sep 25, 2017 at 05:35:05AM -0600, Jan Beulich wrote:
>> >>> On 25.09.17 at 12:49, <wei.liu2@xxxxxxxxxx> wrote:
>> > PIE may (and commonly will) result in the binary being loaded above
>> > the 4Gb boundary, which can't work with at least the VZEROUPPER compat
>> > mode test.
>> > 
>> > Reported-by: Wei Liu <wei.liu2@xxxxxxxxxx>
>> > Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
>> > Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
>> > ---
>> > Cc: Jan Beulich <jbeulich@xxxxxxxx>
>> > Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>> > 
>> > With this patch, vzeroupper passes, but one other test fails.
>> > Testing SSE packed single 64-bit code sequence...[line 368] failed!
>> 
>> Feel free to mail me the binary again, albeit that one's going to
>> be more difficult to debug without being able to see it myself.
>> 
>> > @@ -98,7 +98,9 @@ asm:
>> >  
>> >  asm/%: asm ;
>> >  
>> > -HOSTCFLAGS += $(CFLAGS_xeninclude) -I.
>> > +HOSTCFLAGS-x86_64 :=
>> > +$(call cc-option-add,HOSTCFLAGS,HOSTCC,-no-pie)
>> > +HOSTCFLAGS += $(CFLAGS_xeninclude) -I. $(HOSTCFLAGS-$(XEN_COMPILE_ARCH))
>> 
>> I don't understand this change to my original patch: You now
>> conditionally add -no-pie to HOSTCFLAGS (i.e. also for 32-bit builds),
>> and HOSTCFLAGS-x86_64 remains empty. I also don't see why the
> 
> My bad. The flag should be conditionally added to HOSTCFLAGS-x86_64.
> 
>> addition needs to be conditional: In order to be able to build the
>> entire test, a reasonably new tool chain is needed anyway (much
>> newer than what we require for building everything else). And finally
> 
> It needs to be conditional because not all gcc versions support -no-pie.

You mean older one (which would be no problem, as said) or even
up-to-date ones (due to the way they're being configured)?

>> - is there a difference between -no-pie and -fno-PIE / -fno-pie?
>> 
> 
> I can't tell the difference by reading the manpage TBH. I only know one
> works while the other doesn't by trial and error.

Oh, that's certainly worthwhile adding to the description then.

Jan


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