RFR: 8345296: AArch64: VM crashes with SIGILL when prctl is disallowed [v2]

[Evgeny Astigeevich]

On Mon, 2 Dec 2024 14:17:45 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> src/hotspot/cpu/aarch64/vm_version_aarch64.cpp line 453:
>> 
>>> 451:     } else {
>>> 452:       _initial_sve_vector_length = vl;
>>> 453:     }
>> 
>> I think we need to disable SVE in `VM_Version::get_os_cpu_info` in `src/hotspot/os_cpu/linux_aarch64/vm_version_linux_aarch64.cpp`:
>> 
>> 
>>   if (auxv2 & HWCAP2_SVE2) _features |= CPU_SVE2;
>>   if (auxv2 & HWCAP2_SVEBITPERM) _features |= CPU_SVEBITPERM;
>> 
>>   if (prctl(PR_SVE_GET_VL) == -1) {
>>     warning("Unable to get SVE vector length on this system. Disabling SVE.");
>>     _features &= ~CPU_SVE;
>>   }
>
> I think this part later in the same method does the sync for us already:
> https://github.com/openjdk/jdk/blob/b8233989e7605268dda908e6b639ca373789792b/src/hotspot/cpu/aarch64/vm_version_aarch64.cpp#L590-L597

Maybe it's worth to move your new code under IF at line 518?

if (UseSVE > 0) {
  int vl = get_current_sve_vector_length();
  if ((FLAG_IS_DEFAULT(MaxVectorSize)) {
      MaxVectorSize = vl;
  }

  if (vl < 0) {
     warning("Unable to get SVE vector length on this system. Disabling SVE. Specify -XX:UseSVE=0 to avoid this warning.");
      FLAG_SET_DEFAULT(UseSVE, 0);
  } else if (MaxVectorSize < FloatRegister::sve_vl_min) {
      ...
  }

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/22479#discussion_r1866087358