[Qemu-devel] [Bug 1836078] Re: [PATCH for 4.1] target/arm: report ARMv8.2 FP16 for ARM -cpu max

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

Richard Henderson <richard.henderson@linaro.org> writes:

> On 7/10/19 7:24 PM, Alex Bennée wrote:
>> When we converted to using feature bits in 602f6e42cfbf we missed out
>> the fact (dp && arm_dc_feature(s, ARM_FEATURE_V8)) was supported for
>> -cpu max configurations. This caused a regression in the GCC test
>> suite. Fix this by setting the appropriate FP16 bits in mvfr1.FPHP.
>>
>> Fixes: https://bugs.launchpad.net/qemu/+bug/1836078
>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>> ---
>>  target/arm/cpu.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/target/arm/cpu.c b/target/arm/cpu.c
>> index e75a64a25a..0a0a202fe3 100644
>> --- a/target/arm/cpu.c
>> +++ b/target/arm/cpu.c
>> @@ -2452,6 +2452,10 @@ static void arm_max_initfn(Object *obj)
>>              t = FIELD_DP32(t, ID_ISAR6, SPECRES, 1);
>>              cpu->isar.id_isar6 = t;
>>
>> +            t = cpu->isar.mvfr1;
>> +            t = FIELD_DP32(t, MVFR1, FPHP, 2);     /* v8.2 FP16 */
>
> The comment is wrong.  This is not full v8.2 FP16 support (which would be value
> 3, plus a change to SIMDHP), but v8.0 support for double<->half
> conversions.

Good catch - will fix in v2.
>
> Otherwise,
> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
>
>
> r~


--
Alex Bennée

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https://bugs.launchpad.net/bugs/1836078

Title:
  Regressions on arm-linux-gnueabihf target with some GCC tests

Status in QEMU:
  In Progress

Bug description:
  Hi,

  After trying qemu master:
  commit 474f3938d79ab36b9231c9ad3b5a9314c2aeacde
  Merge: 68d7ff0 14f5d87
  Author: Peter Maydell <email address hidden>
  Date: Fri Jun 21 15:40:50 2019 +0100

  even with the fix for https://bugs.launchpad.net/qemu/+bug/1834496,
  I've noticed several regressions compared to qemu-3.1 when running the GCC testsuite.
  I'm attaching a tarball containing several GCC tests (binaries), needed shared libs, and a short script to run all the tests.

  All tests used to pass w/o error, but with a recent qemu, all of them
  make qemu crash.

  This was noticed with GCC master configured with
  --target arm-none-linux-gnueabihf
  --with-cpu cortex-a57
  --with-fpu crypto-neon-fp-armv8

  Thanks

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