Re: [PATCH] x86/EFI: suppress GNU ld 2.36'es creation of base relocs

[Jan Beulich <jbeulich@xxxxxxxx>]

On 22.02.2021 17:36, Andrew Cooper wrote:
> On 19/02/2021 08:09, Jan Beulich wrote:
>> --- a/xen/arch/x86/Makefile
>> +++ b/xen/arch/x86/Makefile
>> @@ -123,8 +123,13 @@ ifneq ($(efi-y),)
>>  # Check if the compiler supports the MS ABI.
>>  export XEN_BUILD_EFI := $(shell $(CC) $(XEN_CFLAGS) -c efi/check.c -o 
>> efi/check.o 2>/dev/null && echo y)
>>  # Check if the linker supports PE.
>> -XEN_BUILD_PE := $(if $(XEN_BUILD_EFI),$(shell $(LD) -mi386pep 
>> --subsystem=10 -S -o efi/check.efi efi/check.o 2>/dev/null && echo y))
>> +EFI_LDFLAGS = $(patsubst -m%,-mi386pep,$(XEN_LDFLAGS)) --subsystem=10 
>> --strip-debug
>> +XEN_BUILD_PE := $(if $(XEN_BUILD_EFI),$(shell $(LD) $(EFI_LDFLAGS) -o 
>> efi/check.efi efi/check.o 2>/dev/null && echo y))
>>  CFLAGS-$(XEN_BUILD_EFI) += -DXEN_BUILD_EFI
>> +# Check if the linker produces fixups in PE by default (we need to disable 
>> it doing so for now).
>> +XEN_NO_PE_FIXUPS := $(if $(XEN_BUILD_EFI), \
>> +                         $(shell $(LD) $(EFI_LDFLAGS) 
>> --disable-reloc-section -o efi/check.efi efi/check.o 2>/dev/null && \
>> +                                 echo --disable-reloc-section))
> 
> Why does --strip-debug move?

-S and --strip-debug are the same. I'm simply accumulating in
EFI_LDFLAGS all that's needed for the use in the probing construct.

Also I meanwhile have a patch to retain debug info, for which this
movement turns out to be a prereq. (I've yet to test that the
produced binary actually works, and what's more I first need to get
a couple of changes accepted into binutils for the linker to actually
cope.)

> What's wrong with $(call ld-option ...) ?  Actually, lots of this block
> of code looks to be opencoding of standard constructs.

It looks like ld-option could indeed be used here (there are marginal
differences which are likely acceptable), despite its brief comment
talking of just "flag" (singular, plus not really covering e.g. input
files).

But:
- It working differently than cc-option makes it inconsistent to
  use (the setting of XEN_BUILD_EFI can't very well be switched to
  use cc-option); because of this I'm not surprised that we have
  only exactly one use right now in the tree.
- While XEN_BUILD_PE wants to be set to "y", for XEN_NO_PE_FIXUPS
  another transformation would then be necessary to translate "y"
  into "--disable-reloc-section".
- Do you really suggest to re-do this at this point in the release
  cycle?

Jan