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

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

Thomas Huth <thuth@redhat.com> writes:

> On 26/09/2019 01.30, 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 <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 "$cpu" in
>> -  ppc|ppc64|s390|s390x|sparc64|x32|riscv32|riscv64)
>> +  ppc64|s390|s390x|sparc64|riscv64)
>
> I think you can also remove "s390". "s390" is the 32-bit variant,
> "s390x" is the 64-bit variant.
>
>>      supported_cpu="yes"
>>    ;;
>>    ppc64le)
>> @@ -737,7 +737,6 @@ case "$cpu" in
>>    ;;
>>    i386|i486|i586|i686|i86pc|BePC)
>>      cpu="i386"
>> -    supported_cpu="yes"
>>    ;;
>>    x86_64|amd64)
>>      cpu="x86_64"
>> @@ -745,19 +744,22 @@ case "$cpu" in
>>    ;;
>>    armv*b|armv*l|arm)
>>      cpu="arm"
>> -    supported_cpu="yes"
>>    ;;
>>    aarch64)
>>      cpu="aarch64"
>>      supported_cpu="yes"
>>    ;;
>> -  mips*)
>> +  mips64*)
>>      cpu="mips"
>>      supported_cpu="yes"
>>    ;;
>> +  mips*)
>> +    cpu="mips"
>> +  ;;
>>    sparc|sun4[cdmuv])
>>      cpu="sparc"
>> -    supported_cpu="yes"
>> +  ;;
>> +  x32|riscv32)
>
> You forgot to add "ppc" (and "s390") here.
>
>>    ;;
>>    *)
>>      # This will result in either an error or falling back to TCI later
>> @@ -6438,12 +6440,12 @@ if test "$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
>
> In case this gets accepted, we also might want to deprecate the
> qemu-system-i386, qemu-system-arm and qemu-system-ppc targets, since
> they are AFAIK just a subset of qemu-system-x86_64, qemu-system-aarch64
> and qemu-system-ppc64. But that's likely something for a later patch, I
> think.

Yes this is purely for the host side. I'm not intending to deprecate any
guest support.

>
>  Thomas


--
Alex Bennée