Re: [RFC PATCH] configure: deprecate 32 bit build hosts

[Mark Cave-Ayland]

On 26/09/2019 00:30, Alex Bennée wrote:

> The 32 bit hosts are already a second class citizen especially with
> support for running 64 bit guests under TCG. We are also limited by
> testing as actual working 32 bit machines are getting quite rare in
> developers personal menageries. For TCG supporting newer types like
> Int128 is a lot harder with 32 bit calling conventions compared to
> their larger bit sized cousins. Fundamentally address space is the
> most useful thing for the translator to have even for a 32 bit guest a
> 32 bit host is quite constrained.
> 
> As far as I'm aware 32 bit KVM users are even less numerous. Even
> ILP32 doesn't make much sense given the address space QEMU needs to
> manage.
> 
> Lets mark these machines as deprecated so we can have the wailing and
> gnashing of teeth now and look to actually dropping the support in a
> couple of cycles.
> 
> Signed-off-by: Alex Bennée <address@hidden>
> Cc: Richard Henderson <address@hidden>
> ---
>  configure | 24 +++++++++++++-----------
>  1 file changed, 13 insertions(+), 11 deletions(-)
> 
> diff --git a/configure b/configure
> index 542f6aea3f..776fd460b5 100755
> --- a/configure
> +++ b/configure
> @@ -728,7 +728,7 @@ ARCH=
>  # Normalise host CPU name and set ARCH.
>  # Note that this case should only have supported host CPUs, not guests.
>  case "$cpu" in
> -  ppc|ppc64|s390|s390x|sparc64|x32|riscv32|riscv64)
> +  ppc64|s390|s390x|sparc64|riscv64)
>      supported_cpu="yes"
>    ;;
>    ppc64le)
> @@ -737,7 +737,6 @@ case "$cpu" in
>    ;;
>    i386|i486|i586|i686|i86pc|BePC)
>      cpu="i386"
> -    supported_cpu="yes"
>    ;;
>    x86_64|amd64)
>      cpu="x86_64"
> @@ -745,19 +744,22 @@ case "$cpu" in
>    ;;
>    armv*b|armv*l|arm)
>      cpu="arm"
> -    supported_cpu="yes"
>    ;;
>    aarch64)
>      cpu="aarch64"
>      supported_cpu="yes"
>    ;;
> -  mips*)
> +  mips64*)
>      cpu="mips"
>      supported_cpu="yes"
>    ;;
> +  mips*)
> +    cpu="mips"
> +  ;;
>    sparc|sun4[cdmuv])
>      cpu="sparc"
> -    supported_cpu="yes"
> +  ;;
> +  x32|riscv32)
>    ;;
>    *)
>      # This will result in either an error or falling back to TCI later
> @@ -6438,12 +6440,12 @@ if test "$supported_cpu" = "no"; then
>      echo "WARNING: SUPPORT FOR THIS HOST CPU WILL GO AWAY IN FUTURE 
> RELEASES!"
>      echo
>      echo "CPU host architecture $cpu support is not currently maintained."
> -    echo "The QEMU project intends to remove support for this host CPU in"
> -    echo "a future release if nobody volunteers to maintain it and to"
> -    echo "provide a build host for our continuous integration setup."
> -    echo "configure has succeeded and you can continue to build, but"
> -    echo "if you care about QEMU on this platform you should contact"
> -    echo "us upstream at address@hidden."
> +    echo "The QEMU project intends to remove support for all 32 bit host"
> +    echo "CPUs in a future release. 64 bit hosts will need a volunteer"
> +    echo "to maintain it and to provide a build host for our continuous"
> +    echo "integration setup. configure has succeeded and you can continue"
> +    echo "to build, but if you care about QEMU on this platform you"
> +    echo "should contact us upstream at address@hidden."
>  fi
>  
>  if test "$supported_os" = "no"; then

FWIW I still use my Mac Mini G4 (with KVM) to help debug bits of TCG for
qemu-system-ppc and so I would certainly miss this for bits of my Mac work.

Is it possible to reach a compromise based on host/target i.e. allow 32-bit 
hosts to
only run targets up to 32-bits? I'd only ever want to use qemu-system-ppc on 
the Mac
Mini for testing: for qemu-system-ppc64 it is clearly much quicker just to use 
the
nearest x86 box.


ATB,

Mark.