Re: [RFC PATCH 0/2] libtraceevent/perf: Add support for trace-cmd plugins

[Namhyung Kim]

On Mon, 18 Jun 2012 21:03:13 -0400, Steven Rostedt wrote:
> On Tue, 2012-06-19 at 09:45 +0900, Namhyung Kim wrote:
>
>> TRACE_EVENT(kvm_emulate_insn,
>>         ...
>> 	TP_printk("%x:%llx:%s (%s)%s",
>> 		  __entry->csbase, __entry->rip,
>> 		  __print_insn(__entry->insn, __entry->len),
>> 		  __print_symbolic(__entry->flags,
>> 				   kvm_trace_symbol_emul_flags),
>> 		  __entry->failed ? " failed" : ""
>> 		)
>> 	);
>> 
>> And __print_insn is defined as:
>> 
>> #define __print_insn(insn, ilen) ({		                 \
>> 	int i;							 \
>> 	const char *ret = p->buffer + p->len;			 \
>> 								 \
>> 	for (i = 0; i < ilen; ++i)				 \
>> 		trace_seq_printf(p, " %02x", insn[i]);		 \
>> 	trace_seq_printf(p, "%c", 0);				 \
>> 	ret;							 \
>> 	})
>> 
>> The parse error is occurred at the beginning of the compound statment:
>> 
>>   Warning: bad op token {
>>   Warning: failed to read event print fmt for kvm_emulate_insn
>> 
>> I don't think we can handle this kind of compound statments easily. So I
>> just said it *seems* broken. :) Btw, calling trace_seq_printf() here also
>> looks like a problem and I have no idea where the 'p' came from.
>
> This is why we want the plugin. What the plugins do is registers how to
> parse the data of the event. The event format file is still parsed to
> find where the data is located, but the printf fmt: field (TP_printk) is
> ignored. The plugin provides the format to print the data with.
>

Yeah, I know. It's great. :)


> Lets look at the kvm plugin for kvm_emulate_insn:
>
> static int kvm_emulate_insn_handler(struct trace_seq *s, struct record *record,
>                                     struct event_format *event, void *context)
> {
>         unsigned long long rip, csbase, len, flags, failed;
>         int llen;
>         uint8_t *insn;
>         const char *disasm;
>
>         if (pevent_get_field_val(s, event, "rip", record, &rip, 1) < 0)
>                 return -1;
>
>         if (pevent_get_field_val(s, event, "csbase", record, &csbase, 1) < 0)
>                 return -1;
>
>         if (pevent_get_field_val(s, event, "len", record, &len, 1) < 0)
>                 return -1;
>
>         if (pevent_get_field_val(s, event, "flags", record, &flags, 1) < 0)
>                 return -1;
>
>         if (pevent_get_field_val(s, event, "failed", record, &failed, 1) < 0)
>                 return -1;
>
>         insn = pevent_get_field_raw(s, event, "insn", record, &llen, 1);
>         if (!insn)
>                 return -1;
>
>         disasm = disassemble(insn, len, rip,
>                              flags & KVM_EMUL_INSN_F_CR0_PE,
>                              flags & KVM_EMUL_INSN_F_EFL_VM,
>                              flags & KVM_EMUL_INSN_F_CS_D,
>                              flags & KVM_EMUL_INSN_F_CS_L);
>
>         trace_seq_printf(s, "%llx:%llx: %s%s", csbase, rip, disasm,
>                          failed ? " FAIL" : "");
>
>         return 0;
> }
>
>
> You see, this uses the information from libtraceevent to get the
> required fields. Then it prints it out nicely for users. Here's the
> output of trace-cmd report after a trace-cmd record -e kvm and starting
> a guest:
>
>              kvm-6172  [000] 14669573.114126: kvm_entry:            vcpu 0
>              kvm-6172  [000] 14669573.114127: kvm_exit:             reason IO_INSTRUCTION rip 0xffff357a info cfc0008 0
>              kvm-6172  [000] 14669573.114130: kvm_emulate_insn:     0:ffff357a: ec
>              kvm-6172  [000] 14669573.114130: kvm_pio:              pio_read at 0xcfc size 1 count 1
>              kvm-6172  [000] 14669573.114131: kvm_userspace_exit:   reason KVM_EXIT_IO (2)
>              kvm-6172  [000] 14669573.114134: kvm_entry:            vcpu 0
>              kvm-6172  [000] 14669573.114135: kvm_exit:             reason IO_INSTRUCTION rip 0xffff34f9 info cf80003 0
>              kvm-6172  [000] 14669573.114136: kvm_pio:              pio_write at 0xcf8 size 4 count 1
>              kvm-6172  [000] 14669573.114136: kvm_userspace_exit:   reason KVM_EXIT_IO (2)
>
> I can disable plugins to show you the result of what happens without
> them:
>
> trace-cmd report -N
> [...]
>              kvm-6172  [000] 14669573.114126: kvm_entry:            vcpu 0
>              kvm-6172  [000] 14669573.114127: kvm_exit:             [FAILED TO PARSE] exit_reason=30 guest_rip=0xffff357a isa=1 info1=217841672 info2=0
>              kvm-6172  [000] 14669573.114130: kvm_emulate_insn:     [FAILED TO PARSE] rip=4294915450 csbase=0 len=1 insn=Ã[ÃWVS<89>Ã<89>ÃÅ^Gu^Q^O^E flags=5 failed=0
>              kvm-6172  [000] 14669573.114130: kvm_pio:              pio_read at 0xcfc size 1 count 1
>              kvm-6172  [000] 14669573.114131: kvm_userspace_exit:   reason KVM_EXIT_IO (2)
>              kvm-6172  [000] 14669573.114134: kvm_entry:            vcpu 0
>

What I want to do is make it not to fail with default print_fmt (ie. w/o
plugin support). IOW using a plugin to improve things like above is
good, but not using it shouldn't break/fail anything. So I think fixing
the TP_printk is needed.

Thanks,
Namhyung


> This is the power of plugins. I would expect to add something like:
>
> tools/events/plugins/
>
> where these can be added for everyone.
>
> -- Steve
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