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

[Philippe Mathieu-Daudé]

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

  CC      pc-bios/s390-ccw/main.o
clang: warning: optimization flag '-fno-delete-null-pointer-checks' is
not supported [-Wignored-optimization-argument]
clang: warning: argument unused during compilation: '-msoft-float'
[-Wunused-command-line-argument]
/home/travis/build/qemu/qemu/pc-bios/s390-ccw/main.c:284:5: warning: no
previous prototype for function 'main' [-Wmissing-prototypes]
int main(void)
    ^
1 warning generated.
clang: warning: optimization flag '-fno-delete-null-pointer-checks' is
not supported [-Wignored-optimization-argument]

  CC      pc-bios/s390-ccw/jump2ipl.o
/home/travis/build/qemu/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/qemu/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