Re: [Qemu-devel] [RFC v7 12/16] configure: Use slow-path for atomic only when the softmmu is enabled

["Alex Bennée" <alex.bennee@linaro.org>]

Alex Bennée <alex.bennee@linaro.org> writes:

> Alvise Rigo <a.rigo@virtualopensystems.com> writes:
>
>> Use the new slow path for atomic instruction translation when the
>> softmmu is enabled.
>>
>> At the moment only arm and aarch64 use the new LL/SC backend. It is
>> possible to disable such backed with --disable-arm-llsc-backend.
>
> Do we want to disable the backend once it is merged? Does it serve a
> purpose other than to confuse the user?

Also this needs to be after the actual implementation has been filled in
or you'll have a broken build!

>
>>
>> Suggested-by: Jani Kokkonen <jani.kokkonen@huawei.com>
>> Suggested-by: Claudio Fontana <claudio.fontana@huawei.com>
>> Signed-off-by: Alvise Rigo <a.rigo@virtualopensystems.com>
>> ---
>>  configure | 14 ++++++++++++++
>>  1 file changed, 14 insertions(+)
>>
>> diff --git a/configure b/configure
>> index 44ac9ab..915efcc 100755
>> --- a/configure
>> +++ b/configure
>> @@ -294,6 +294,7 @@ solaris="no"
>>  profiler="no"
>>  cocoa="no"
>>  softmmu="yes"
>> +arm_tcg_use_llsc="yes"
>>  linux_user="no"
>>  bsd_user="no"
>>  aix="no"
>> @@ -880,6 +881,10 @@ for opt do
>>    ;;
>>    --disable-debug-tcg) debug_tcg="no"
>>    ;;
>> +  --enable-arm-llsc-backend) arm_tcg_use_llsc="yes"
>> +  ;;
>> +  --disable-arm-llsc-backend) arm_tcg_use_llsc="no"
>> +  ;;
>>    --enable-debug)
>>        # Enable debugging options that aren't excessively noisy
>>        debug_tcg="yes"
>> @@ -4751,6 +4756,7 @@ echo "host CPU          $cpu"
>>  echo "host big endian   $bigendian"
>>  echo "target list       $target_list"
>>  echo "tcg debug enabled $debug_tcg"
>> +echo "arm use llsc backend" $arm_tcg_use_llsc
>>  echo "gprof enabled     $gprof"
>>  echo "sparse enabled    $sparse"
>>  echo "strip binaries    $strip_opt"
>> @@ -4806,6 +4812,7 @@ echo "Install blobs     $blobs"
>>  echo "KVM support       $kvm"
>>  echo "RDMA support      $rdma"
>>  echo "TCG interpreter   $tcg_interpreter"
>> +echo "use ld/st excl    $softmmu"
>
> I think we can drop everything above here.
>
>>  echo "fdt support       $fdt"
>>  echo "preadv support    $preadv"
>>  echo "fdatasync         $fdatasync"
>> @@ -5863,6 +5870,13 @@ fi
>>  echo "LDFLAGS+=$ldflags" >> $config_target_mak
>>  echo "QEMU_CFLAGS+=$cflags" >> $config_target_mak
>>
>> +# Use tcg LL/SC tcg backend for exclusive instruction is arm/aarch64
>> +# softmmus targets
>> +if test "$arm_tcg_use_llsc" = "yes" ; then
>> +  if test "$target" = "arm-softmmu" ; then
>> +    echo "CONFIG_ARM_USE_LDST_EXCL=y" >> $config_target_mak
>> +  fi
>> +fi
>
> This isn't going to be just ARM specific and it will be progressively
> turned on for other arches. So perhaps with the CONFIG_SOFTMMU section:
>
> if test "$target_softmmu" = "yes" ; then
>     echo "CONFIG_SOFTMMU=y" >> $config_target_mak
>
>     # Use SoftMMU LL/SC primitives?
>     case "$target_name" in
>         arm | aarch64)
>             echo "CONFIG_USE_LDST_EXCL=y" >> $config_target_mak
>             ;;
>     esac
> fi
>
>
>>  done # for target in $targets
>>
>>  if [ "$pixman" = "internal" ]; then


--
Alex Bennée