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

[Alex Bennée]

Alvise Rigo <address@hidden> 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?

>
> Suggested-by: Jani Kokkonen <address@hidden>
> Suggested-by: Claudio Fontana <address@hidden>
> Signed-off-by: Alvise Rigo <address@hidden>
> ---
>  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