Re: [Xen-devel] [XEN PATCH for-4.13] xen: Fix race to build arch/x86/efi/relocs-dummy.o

[Jan Beulich <jbeulich@xxxxxxxx>]

On 14.11.2019 19:05, Anthony PERARD wrote:
> With $(TARGET).efi depending on efi/relocs-dummy.o, arch/x86/Makefile
> will attempt to build that object. This result in the dependency file
> been generated with relocs-dummy.o depending on efi/relocs-dummy.o.
> 
> Then, when arch/x86/efi/Makefile tries to build relocs-dummy.o, well
> efi/relocs-dummy.S doesn't exist.
> 
> Have only one makefile responsible for building relocs-dummy.o.

On a system with too old a tool chain for the EFI build to get
enabled I now get about a dozen instances per build of

nm: 'efi/relocs-dummy.o': No such file

I don't suppose you did try out your change in such an oldish
environment? I assume the problem are these two lines:

$(TARGET).efi: VIRT_BASE = 0x$(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')

I'm not sure it is well defined when make would evaluate such
target specific variable assignments (i.e. I'm not sure this
doesn't point out an issue even on EFI capable tool chains).
Then again these not using := should cause them to get
evaluated only upon use, i.e. never. But that's clearly not
the case here; of course make is also the now pretty dated
3.81 one.

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