[PATCH v6 3/5] x86/mce, EDAC/mce_amd: Add support for new MCA_SYND{1,2} registers

["Naik, Avadhut" <avadnaik@amd.com>]

On 10/17/2024 02:09, Zhuo, Qiuxu wrote:
>> From: Avadhut Naik <avadhut.naik@amd.com>
>> [...]
>> --- a/include/trace/events/mce.h
>> +++ b/include/trace/events/mce.h
>> @@ -43,6 +43,7 @@ TRACE_EVENT(mce_record,
>>  		__field(	u8,		bank		)
>>  		__field(	u8,		cpuvendor	)
>>  		__field(	u32,		microcode	)
>> +		__dynamic_array(u8, v_data, sizeof(err->vendor))
>>  	),
>>
>>  	TP_fast_assign(
>> @@ -65,9 +66,10 @@ TRACE_EVENT(mce_record,
>>  		__entry->bank		= err->m.bank;
>>  		__entry->cpuvendor	= err->m.cpuvendor;
>>  		__entry->microcode	= err->m.microcode;
>> +		memcpy(__get_dynamic_array(v_data), &err->vendor,
>> +sizeof(err->vendor));
>>  	),
>>
>> -	TP_printk("CPU: %d, MCGc/s: %llx/%llx, MC%d: %016Lx, IPID: %016Lx,
>> ADDR: %016Lx, MISC: %016Lx, SYND: %016Lx, RIP: %02x:<%016Lx>, TSC: %llx,
>> PPIN: %llx, vendor: %u, CPUID: %x, time: %llu, socket: %u, APIC: %x,
>> microcode: %x",
>> +	TP_printk("CPU: %d, MCGc/s: %llx/%llx, MC%d: %016llx, IPID: %016llx,
>> +ADDR: %016llx, MISC: %016llx, SYND: %016llx, RIP: %02x:<%016llx>, TSC:
>> +%llx, PPIN: %llx, vendor: %u, CPUID: %x, time: %llu, socket: %u, APIC:
>> +%x, microcode: %x, vendor data: %s",
>>  		__entry->cpu,
>>  		__entry->mcgcap, __entry->mcgstatus,
>>  		__entry->bank, __entry->status,
>> @@ -83,7 +85,8 @@ TRACE_EVENT(mce_record,
>>  		__entry->walltime,
>>  		__entry->socketid,
>>  		__entry->apicid,
>> -		__entry->microcode)
>> +		__entry->microcode,
>> +		__print_dynamic_array(v_data, 8))
> 
> What is the 2nd parameter '8' about? 
> 
> The 2nd parameter is about the element size. 
> The element type is 'u8', as defined above. 
> Therefore:
> 
>     __print_dynamic_array(v_data, sizeof(u8)))
>     
> -Qiuxu
> 
IIUC, the second parameter above determines how the dynamic
array is parsed and logged. The value of 8 means that the
array will be traversed with a u64 pointer i.e. data within
the array will be logged by the tracepoint in chunks of 8
bytes. Something like below:

vendor data: {0x3a726f7461636f4c,0x30434d305020,0x27000003fd}

This seems convenient since, AFAIK, MCA registers on x86-64
are of 8 bytes.

If we use sizeof(u8) (which equates to 1) above, then u8
pointer will be used for traversing the dynamic array and each
byte within the registers will be logged individually.
Something like below.

vendor data: {0x4c,0x6f,0x63,0x61,0x74,0x6f,0x72,0x3a,0x20,0x50,0x30,0x4d,0x43,0x30,0x0,0x0,0xfd,0x3,0x0,0x0,0x27,0x0,0x0,0x0}

Combined with endianness of the processor, this seems somewhat
inconvenient to decipher. Would you agree?

> [...]

-- 
Thanks,
Avadhut Naik