RFR: JDK-8288824: [arm32] Display isetstate in register output

[Thomas Stuefe]

On Tue, 5 Jul 2022 08:30:17 GMT, Dmitry Samersoff <dsamersoff at openjdk.org> wrote:

>> When analyzing [JDK-8288719](https://bugs.openjdk.org/browse/JDK-8288719), to know the current isetstate was useful. It would be nice if that were printed clearly in the register output to save some mental cycles parsing CPSR.
>> 
>> Looks like this:
>> 
>> Registers:
>>   r0  = 0x00000000
>>   r1  = 0xbe9e7fb8
>>   r2  = 0x00000000
>>   r3  = 0xb6f860ac
>>   r4  = 0xbe9e7fb8
>>   r5  = 0xb6f864e0
>>   r6  = 0xbe9e8060
>>   r7  = 0xbe9e7fb0
>>   r8  = 0xb6da8798
>>   r9  = 0x00000000
>>   r10 = 0x00000000
>>   fp  = 0x00000001
>>   r12 = 0xb6da87ec
>>   sp  = 0xbe9e7fb0
>>   lr  = 0xb6bc7dfb
>>   pc  = 0xb6bc7dfa
>>   cpsr = 0x800e0030
>> isetstate: Thumb
>> 
>> Registers:
>>   r0  = 0xb6be3664
>>   r1  = 0xbe947c70
>>   r2  = 0x00000058
>>   r3  = 0xb6f3e000
>>   r4  = 0xbe947c70
>>   r5  = 0xb6f3f510
>>   r6  = 0xb6c95bdc
>>   r7  = 0xbe947d18
>>   r8  = 0xbe947d98
>>   r9  = 0x00000000
>>   r10 = 0x00000000
>>   fp  = 0xbe947d14
>>   r12 = 0xb6c95f84
>>   sp  = 0xbe947c68
>>   lr  = 0xb6e97218
>>   pc  = 0xb6793f3c
>>   cpsr = 0x60000010
>> isetstate: ARM 
>> 
>> 
>> I refrained from parsing more information from the CPSR because I did not want to blow up the patch. ISETSTATE proved to be useful. More information can be added if needed.
>
> src/hotspot/os_cpu/linux_arm/os_linux_arm.cpp line 459:
> 
>> 457:   case 2: st->print_cr("Jazelle"); break;
>> 458:   case 3: st->print_cr("ThumbEE"); break;
>> 459:   default: ShouldNotReachHere();
> 
> Should we print here something like "undefined" rather than abort VM?

Hi Dmitry,

I think this cannot happen, since isetstate is the combination of two bits (see line 451 ff). So an assert would be correct here, since this can only fire if we break that assumption by changing isetstate with a future patch.

But I am unemotional. If you prefer not to assert, I can use "undefined".

Cheers, Thomas

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PR: https://git.openjdk.org/jdk/pull/9223