Re: [Xen-devel] [PATCH] x86/efi: move the logic to detect PE build support

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.07.18 at 10:26, <roger.pau@xxxxxxxxxx> wrote:
> On Mon, Jul 16, 2018 at 01:59:15AM -0600, Jan Beulich wrote:
>> >>> On 13.07.18 at 18:02, <roger.pau@xxxxxxxxxx> wrote:
>> > --- a/xen/arch/x86/Makefile
>> > +++ b/xen/arch/x86/Makefile
>> > @@ -168,6 +168,16 @@ $(TARGET).efi: ALT_BASE = 0x$(shell $(NM) 
>> > efi/relocs-dummy.o | sed -n 's, A ALT_
>> >  # Don't use $(wildcard ...) here - at least make 3.80 expands this too 
> early!
>> >  $(TARGET).efi: guard = $(if $(shell echo efi/dis* | grep disabled),:)
>> >  
>> > +# Check if the build system supports PE.
>> > +efi := y$(shell rm -f efi/disabled)
>> > +efi := $(if $(efi),$(shell $(CC) $(filter-out $(CFLAGS-y) .%.d,$(CFLAGS)) 
>> > -c 
> efi/check.c -o efi/check.o 2>efi/disabled && echo y))
>> > +efi := $(if $(efi),$(shell $(LD) -mi386pep --subsystem=10 -o 
>> > efi/check.efi 
> efi/check.o 2>efi/disabled && echo y))
>> > +efi := $(if $(efi),$(shell rm efi/disabled)y)
>> > +export BUILD_PE := $(efi)
>> > +ifeq ($(efi),y)
>> > +CFLAGS += -DBUILD_PE
>> > +endif
>> 
>> For one I'm not really happy about this being moved here: I did place it
>> in efi/Makefile for the simple reason of having as much as possible of
>> the EFI specifics in that single file.
>> 
>> Additionally I think it would be better if setting propagated through the
>> environment had XEN_ prefixes.
>> 
>> > --- a/xen/arch/x86/xen.lds.S
>> > +++ b/xen/arch/x86/xen.lds.S
>> > @@ -304,7 +304,9 @@ SECTIONS
>> >    } :text
>> >  #endif
>> >  
>> > -  efi = DEFINED(efi) ? efi : .;
>> > +#ifndef BUILD_PE
>> > +  efi = .;
>> > +#endif
>> 
>> And then I don't really understand how this is different from the
>> original #ifndef EFI that Daniel had problems with.
> 
> As I understand it EFI only signals whether a PE binary will be
> created,

But that is my point: BUILD_PE signals exactly that aiui.

Jan

> but the ELF binary will also contain efi support if the
> build toolchain supports PE. Hence whether the efi symbol is defined
> or not solely depends on the detection done above (and whether
> runtime.c or stub.c is used).
> 
> Maybe I'm missing something, I have to admit the code is quite
> convoluted.
> 
> Thanks, Roger.





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