Re: [Xen-devel] [XEN PATCH] xen/arch/x86/Makefile: Remove $(guard) use from $(TARGET).efi target

[Jan Beulich <jbeulich@xxxxxxxx>]

On 19.11.2019 18:58, Anthony PERARD wrote:
> Following the patch 65d104984c04 ("x86: fix race to build
> arch/x86/efi/relocs-dummy.o"), the error message
>   nm: 'efi/relocs-dummy.o': No such file"
> started to appear on system which can't build the .efi target. This is
> because relocs-dummy.o isn't built anymore.
> The error is printed by the evaluation of VIRT_BASE and ALT_BASE which
> aren't use anyway.
> 
> But, we don't need that file as we don't want to build `$(TARGET).efi'
> anyway.  On such system, $(guard) evaluate to the shell builtin ':',
> which prevent any of the shell commands in `$(TARGET).efi' from been
> executed.
> 
> Even if $(guard) is evaluated opon use, it depends on $(XEN_BUILD_PE)
> which is evaluated at the assignment. So, we can replace $(guard) in
> $(TARGET).efi by having two different rules depending on
> $(XEN_BUILD_PE) instead.
> 
> The change with this patch is that none of the dependency of
> $(TARGET).efi will be built if the linker doesn't support PE
> and VIRT_BASE and ALT_BASE don't get evaluated anymore, so nm will not
> complain about the missing relocs-dummy.o file anymore.
> 
> Since prelink-efi.o isn't built on system that can't build
> $(TARGET).efi anymore, we can remove the $(guard) variable everywhere.

And indeed the need for it had disappeared with 18cd4997d2 ("x86/efi:
move the logic to detect PE build support").

> Reported-by: Jan Beulich <jbeulich@xxxxxxxx>
> Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Also Cc-ing Jürgen, as this addresses a (cosmetic) regression from
65d104984c ("x86: fix race to build arch/x86/efi/relocs-dummy.o").

> @@ -178,8 +178,6 @@ CFLAGS-$(XEN_BUILD_EFI) += -DXEN_BUILD_EFI
>  
>  $(TARGET).efi: VIRT_BASE = 0x$(shell $(NM) efi/relocs-dummy.o | sed -n 's, A 
> VIRT_START$$,,p')
>  $(TARGET).efi: ALT_BASE = 0x$(shell $(NM) efi/relocs-dummy.o | sed -n 's, A 
> ALT_START$$,,p')
> -# Don't use $(wildcard ...) here - at least make 3.80 expands this too early!
> -$(TARGET).efi: guard = $(if $(filter y,$(XEN_BUILD_PE)),,:)

It is particularly telling that the comment here had been stale
as of that earlier change from Roger, as the (shell level)
wildcard use was the whole reason for needing $(guard) here.

Jan

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