Re: [Qemu-devel] [PATCH v2 01/15] configure: add the disable-tcg option

["Daniel P. Berrange" <berrange@redhat.com>]

On Mon, Jul 03, 2017 at 06:12:09PM +0800, Yang Zhong wrote:
> Add the disable-tcg option into configure and echo CONFIG_TCG=y into
> $config_target_mak. The default tcg is enabled for all build, only i386
> and x86_64 softmmu option can be disabled. This operation do not make
> big change with the older build command.
> 
> The new configure build command like below
> (1)./configure
>    tcg is defaultly enabled
> 
> (2)./configure --disable-tcg --target-list=x86_64-softmmu
>    tcg is disabled in x86_64-softmmu
> 
> (3)./configure --disable-tcg --target-list=i386-softmmu
>    tcg is disabled in i386-softmmu
> 
> If the --target-list include other softmmus or user options, the configure
> command will report error and configure is aborted.
> The error as:
> ERROR: The current aarch64-softmmu can't support disable-tcg,
>     only i386-softmmu|x86_64-softmmu support disable-tcg
> or
> ERROR: The user build can't support disable-tcg,
>     only i386-softmmu|x86_64-softmmu support disable-tcg
> 
> Signed-off-by: Yang Zhong <yang.zhong@intel.com>
> ---
>  configure | 43 ++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 42 insertions(+), 1 deletion(-)
> 
> diff --git a/configure b/configure
> index c571ad1..61ce514 100755
> --- a/configure
> +++ b/configure
> @@ -224,6 +224,7 @@ cap_ng=""
>  attr=""
>  libattr=""
>  xfs=""
> +tcg="yes"
>  
>  vhost_net="no"
>  vhost_scsi="no"
> @@ -953,6 +954,10 @@ for opt do
>    ;;
>    --enable-hax) hax="yes"
>    ;;
> +  --disable-tcg) tcg="no"
> +  ;;
> +  --enable-tcg) tcg="yes"
> +  ;;
>    --disable-tcg-interpreter) tcg_interpreter="no"
>    ;;
>    --enable-tcg-interpreter) tcg_interpreter="yes"
> @@ -1715,6 +1720,24 @@ case " $target_list " in
>    ;;
>  esac
>  
> +if test "$tcg" = "no"; then
> +   for target in $target_list; do
> +      if test "$softmmu" = "yes"; then
> +        case $target in
> +           i386-softmmu|x86_64-softmmu)
> +           ;;
> +        *)
> +           error_exit "The current $target can't support disable-tcg,"\
> +              "only i386-softmmu|x86_64-softmmu support disable-tcg"
> +           ;;

This looks too simplistic in its logic.

You can disable TCG, if-and-only-if the system emulator supports KVM.

KVM is supported on many architectures, not only x86-64 & i386.

KVM is only supported if the guest emulator architecture matches the
host build target architecture.

ie if you are building an x86_64 system emulator on a PPC64 host,
then you can't disable TCG.

So this needs rewriting to *not* special case x86_64 / i386. Instead
you need to compare & match build target / system emulator architectures,
across all architectures supporting KVM.

Regards,
Daniel
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