Re: [RFC PATCH] configure: deprecate 32 bit build hosts - Philippe Mathieu-Daudé

From: "Philippe Mathieu-Daudé" <philmd@redhat.com>
To: "Alex Bennée" <alex.bennee@linaro.org>, qemu-devel@nongnu.org
Cc: qemu-riscv@nongnu.org,
	Richard Henderson <richard.henderson@linaro.org>,
	qemu-discuss@nongnu.org, qemu-s390x@nongnu.org,
	qemu-arm@nongnu.org, qemu-ppc@nongnnu.org
Subject: Re: [RFC PATCH] configure: deprecate 32 bit build hosts
Date: Thu, 26 Sep 2019 09:29:11 +0200	[thread overview]
Message-ID: <e08a9d80-a797-76a9-b1e5-6ccbef0b1c37@redhat.com> (raw)
In-Reply-To: <20190925233013.6449-1-alex.bennee@linaro.org>

On 9/26/19 1:30 AM, 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 <alex.bennee@linaro.org>
> Cc: Richard Henderson <richard.henderson@linaro.org>
> ---
>  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"

I think linux-user is quite used in embedded stuff such NAS.

Eventually this public don't need edge QEMU, it might keep using QEMU
v5.0.stable until all NAS/embedded devices are 64-bit...

>    ;;
>    aarch64)
>      cpu="aarch64"
>      supported_cpu="yes"
>    ;;
> -  mips*)
> +  mips64*)
>      cpu="mips"
>      supported_cpu="yes"
>    ;;
> +  mips*)
> +    cpu="mips"

Similarly I can imagine linux-user being used on some routers.

> +  ;;
>    sparc|sun4[cdmuv])
>      cpu="sparc"
> -    supported_cpu="yes"
> +  ;;
> +  x32|riscv32)

x32 is borderline :) but yes, pointers are 32-bit.

>    ;;
>    *)
>      # 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 $cpu support is not currently maintained."
> -    echo "The QEMU project intends to remove support for this host CPU in"
> -    echo "a future release if nobody volunteers to maintain it and to"
> -    echo "provide a build host for our continuous integration setup."
> -    echo "configure has succeeded and you can continue to build, but"
> -    echo "if you care about QEMU on this platform you should contact"
> -    echo "us upstream at qemu-devel@nongnu.org."
> +    echo "The QEMU project intends to remove support for all 32 bit host"
> +    echo "CPUs in a future release. 64 bit hosts will need a volunteer"
> +    echo "to maintain it and to provide a build host for our continuous"
> +    echo "integration setup. configure has succeeded and you can continue"
> +    echo "to build, but if you care about QEMU on this platform you"
> +    echo "should contact us upstream at qemu-devel@nongnu.org."
>  fi
>  
>  if test "$supported_os" = "no"; then
> 