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

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 5/12/21 1:53 PM, 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

Using clang-10:

C compiler for the host machine: clang-10 (clang 10.0.0-4ubuntu1 "clang
version 10.0.0-4ubuntu1~18.04.2 ")
C linker for the host machine: clang-10 ld.bfd 2.30
C++ compiler for the host machine: clang++-10 (clang 10.0.0-4ubuntu1
"clang version 10.0.0-4ubuntu1~18.04.2 ")
C++ linker for the host machine: clang++-10 ld.bfd 2.30
[...]
  Compilation
                         host CPU: s390x
                  host endianness: big
                       C compiler: clang-10
                  Host C compiler: clang-10
                     C++ compiler: clang++-10

clang-10 -Wall -Wstrict-prototypes -Wredundant-decls -Wundef
-Wwrite-strings -Wmissing-prototypes -Wold-style-definition
-Wtype-limits -Wformat-security -Wformat-y2k -Winit-self
-Wignored-qualifiers -Wempty-body -Wnested-externs -Wendif-labels
-Wexpansion-to-defined -Wno-initializer-overrides
-Wno-missing-include-dirs -Wno-shift-negative-value -Wno-string-plus-int
-Wno-typedef-redefinition -Wno-tautological-type-limit-compare
-ffreestanding -fno-delete-null-pointer-checks -fno-common -fPIE -fwrapv
-fno-strict-aliasing -fno-asynchronous-unwind-tables
-fno-stack-protector -msoft-float -march=z10 -std=gnu99 -nostdinc
-I/home/travis/build/philmd/qemu/roms/SLOF/lib/libc/include
-I/home/travis/build/philmd/qemu/roms/SLOF/lib/libnet -MMD -MP -MT
jump2ipl.o -MF ./jump2ipl.d -O2 -g -c -o jump2ipl.o
/home/travis/build/philmd/qemu/pc-bios/s390-ccw/jump2ipl.c
clang: warning: argument unused during compilation: '-msoft-float'
[-Wunused-command-line-argument]
/home/travis/build/philmd/qemu/pc-bios/s390-ccw/jump2ipl.c:67:18: error:
invalid operand for instruction
    asm volatile("lghi 1,1\n\t"
                 ^
<inline asm>:1:7: note: instantiated into assembly here
        lghi 1,1
             ^
/home/travis/build/philmd/qemu/pc-bios/s390-ccw/jump2ipl.c:67:29: error:
invalid operand for instruction
    asm volatile("lghi 1,1\n\t"
                            ^
<inline asm>:2:7: note: instantiated into assembly here
        diag 1,1,0x308
             ^
2 errors generated.
Makefile:20: recipe for target 'jump2ipl.o' failed
make[1]: *** [jump2ipl.o] Error 1