Re: [kvm-unit-tests PATCH 1/7] x86: Makefile: Allow division on x86_64-elf binutils

[Roman Bolshakov <r.bolshakov@yadro.com>]

On Fri, Aug 28, 2020 at 09:56:28AM +0200, Thomas Huth wrote:
> On 28/08/2020 09.47, Roman Bolshakov wrote:
> > On Fri, Aug 28, 2020 at 09:24:10AM +0200, Thomas Huth wrote:
> >> On 28/08/2020 08.54, Roman Bolshakov wrote:
> >>> On Fri, Aug 28, 2020 at 07:00:19AM +0200, Thomas Huth wrote:
> >>>> On 10/08/2020 15.06, Roman Bolshakov wrote:
> >>>>> For compatibility with other SVR4 assemblers, '/' starts a comment on
> >>>>> *-elf binutils target and thus division operator is not allowed [1][2].
> >>>>> That breaks cstart64.S build:
> >>>>>
> >>>>>   x86/cstart64.S: Assembler messages:
> >>>>>   x86/cstart64.S:294: Error: unbalanced parenthesis in operand 1.
> >>>>>
> >>>>> The option is ignored on the Linux target of GNU binutils.
> >>>>>
> >>>>> 1. https://sourceware.org/binutils/docs/as/i386_002dChars.html
> >>>>> 2. https://sourceware.org/binutils/docs/as/i386_002dOptions.html#index-_002d_002ddivide-option_002c-i386
> >>>>>
> >>>>> Cc: Cameron Esfahani <dirty@apple.com>
> >>>>> Signed-off-by: Roman Bolshakov <r.bolshakov@yadro.com>
> >>>>> ---
> >>>>>  x86/Makefile | 2 ++
> >>>>>  1 file changed, 2 insertions(+)
> >>>>>
> >>>>> diff --git a/x86/Makefile b/x86/Makefile
> >>>>> index 8a007ab..22afbb9 100644
> >>>>> --- a/x86/Makefile
> >>>>> +++ b/x86/Makefile
> >>>>> @@ -1 +1,3 @@
> >>>>>  include $(SRCDIR)/$(TEST_DIR)/Makefile.$(ARCH)
> >>>>> +
> >>>>> +COMMON_CFLAGS += -Wa,--divide
> >>>>
> >>>> Some weeks ago, I also played with an elf cross compiler and came to the
> >>>> same conclusion, that we need this option there. Unfortunately, it does
> >>>> not work with clang:
> >>>>
> >>>>  https://gitlab.com/huth/kvm-unit-tests/-/jobs/707986800#L1629
> >>>>
> >>>> You could try to wrap it with "cc-option" instead ... or use a proper
> >>>> check in the configure script to detect whether it's needed or not.
> >>>>
> >>>
> >>> Hi Thomas,
> >>>
> >>> Thanks for reviewing the series. I'll look into both options and will
> >>> test with both gcc and clang afterwards. I can also update .travis.yml
> >>> in a new patch to test the build on macOS.
> >>
> >> That would be great, thanks! Note that you need at least Clang v10 (the
> >> one from Fedora 32 is fine) to compile the kvm-unit-tests.
> >>
> >> And if it's of any help, this was the stuff that I used in .travis.yml
> >> for my experiments (might still be incomplete, though):
> >>
> >>     - os: osx
> >>       osx_image: xcode12
> >>       addons:
> >>         homebrew:
> >>           packages:
> >>             - bash
> >>             - coreutils
> >>             - qemu
> >>             - x86_64-elf-gcc
> >>       env:
> >>       - CONFIG="--cross-prefix=x86_64-elf-"
> >>       - BUILD_DIR="build"
> >>       - TESTS="umip"
> >>       - ACCEL="tcg"
> >>
> >>     - os: osx
> >>       osx_image: xcode12
> >>       addons:
> >>         homebrew:
> >>           packages:
> >>             - bash
> >>             - coreutils
> >>             - qemu
> >>             - i386-elf-gcc
> > 
> > It's going to be i686-elf-gcc.
> 
> Ah, there are two flavours? Ok, good to know.
> 

i386-elf-gcc package was configured as x86_64-pc-elf target and then was
renamed to x86_64-elf-gcc to match GCC target name (last December or in
January).

x86_64_elf-gcc can't properly link 32-bit ELF binaries because of GCC
PR16470
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=16470), PR32044
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=32044). A cross-compiler
is needed for that, that's why i686-elf-gcc was added in June/May:

https://github.com/Homebrew/homebrew-core/pull/54946/commits/94ee559e6c6284539f74662a85ec20c174436677

But as far as I understand i686-pc-elf target is the same as i386-pc-elf
in GCC/binutils (according to code inspection and a following discussion
freenode's #gcc channel).

FWIW, i686-elf-gcc can be installed in parallel with x86_64-elf-gcc.

Thanks,
Roman