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

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Jul 16, 2018 at 02:55:16AM -0600, Jan Beulich wrote:
> >>> 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.

No, BUILD_PE signals whether the binary will use runtime.c instead of
stub.c, and thus have the efi symbol defined. It is my understanding
from the previous conversation with Daniel that for multiboot2 support
you need an EFL binary that contains runtime.c (and thus the efi
symbol is defined), and that you can build such a binary without
having EFI set.

Roger.

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