Re: [PULL 8/9] pc-bios/s390-ccw: Allow building with Clang, too

[Thomas Huth <thuth@redhat.com>]

On 12/05/2021 13.53, Philippe Mathieu-Daudé wrote:
> On 5/10/21 9:35 AM, Thomas Huth wrote:
>> Clang unfortunately does not support generating code for the z900
>> architecture level and starts with the z10 instead. Thus to be able
>> to support compiling with Clang, we have to check for the supported
>> compiler flags. The disadvantage is of course that the bios image
>> will only run with z10 guest CPUs upwards (which is what most people
>> use anyway), so just in case let's also emit a warning in that case
>> (we will continue to ship firmware images that have been pre-built
>> with GCC in future releases, so this should not impact normal users,
>> too).
>>
>> Message-Id: <20210502174836.838816-5-thuth@redhat.com>
>> Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
>> Signed-off-by: Thomas Huth <thuth@redhat.com>
>> ---
>>   configure                 | 9 ++++++++-
>>   pc-bios/s390-ccw/Makefile | 3 ++-
>>   2 files changed, 10 insertions(+), 2 deletions(-)
>>
>> diff --git a/configure b/configure
>> index 4f374b4889..5ebc937746 100755
>> --- a/configure
>> +++ b/configure
>> @@ -5417,9 +5417,16 @@ if { test "$cpu" = "i386" || test "$cpu" = "x86_64"; } && \
>>   fi
>>   
>>   # Only build s390-ccw bios if we're on s390x and the compiler has -march=z900
>> +# or -march=z10 (which is the lowest architecture level that Clang supports)
>>   if test "$cpu" = "s390x" ; then
>>     write_c_skeleton
>> -  if compile_prog "-march=z900" ""; then
>> +  compile_prog "-march=z900" ""
>> +  has_z900=$?
>> +  if [ $has_z900 = 0 ] || compile_prog "-march=z10" ""; then
>> +    if [ $has_z900 != 0 ]; then
>> +      echo "WARNING: Your compiler does not support the z900!"
>> +      echo "         The s390-ccw bios will only work with guest CPUs >= z10."
>> +    fi
>>       roms="$roms s390-ccw"
>>       # SLOF is required for building the s390-ccw firmware on s390x,
>>       # since it is using the libnet code from SLOF for network booting.
>> diff --git a/pc-bios/s390-ccw/Makefile b/pc-bios/s390-ccw/Makefile
>> index 83fb1afb73..cee9d2c63b 100644
>> --- a/pc-bios/s390-ccw/Makefile
>> +++ b/pc-bios/s390-ccw/Makefile
>> @@ -34,7 +34,8 @@ QEMU_CFLAGS += $(call cc-option,-Werror $(QEMU_CFLAGS),-Wno-stringop-overflow)
>>   QEMU_CFLAGS += -ffreestanding -fno-delete-null-pointer-checks -fno-common -fPIE
>>   QEMU_CFLAGS += -fwrapv -fno-strict-aliasing -fno-asynchronous-unwind-tables
>>   QEMU_CFLAGS += $(call cc-option, $(QEMU_CFLAGS), -fno-stack-protector)
>> -QEMU_CFLAGS += -msoft-float -march=z900
>> +QEMU_CFLAGS += -msoft-float
>> +QEMU_CFLAGS += $(call cc-option, $(QEMU_CFLAGS),-march=z900,-march=z10)
>>   QEMU_CFLAGS += -std=gnu99
>>   LDFLAGS += -Wl,-pie -nostdlib
> 
> This broke the travis-ci  "[s390x] Clang (disable-tcg)" job:
> https://travis-ci.org/github/qemu/qemu/jobs/770794417#L1776
> 
> Description:	Ubuntu 18.04.4 LTS
> Release:	18.04
> Codename:	bionic
> 
> $ clang --version
> clang version 6.0.0-1ubuntu2 (tags/RELEASE_600/final)
> Target: s390x-ibm-linux-gnu

Darn! ... I guess we should switch to the clang-10 package which should be 
available there, since Daniel also plans to raise the minimum Clang version 
to 7.0 now ... I'll try to come up with a patch...

  Thomas