linux-kernel - Re: [RFC/PATCH] perf: Add sizeof operator support

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Date:	Fri, 17 Jun 2016 13:57:44 -0500
From:	Jeremy Linton <jeremy.linton@....com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, acme@...hat.com, namhyung@...nel.org,
	kapileshwar.singh@....com, scottwood@...escale.com,
	hekuang@...wei.com
Subject: Re: [RFC/PATCH] perf: Add sizeof operator support

On 06/17/2016 11:50 AM, Steven Rostedt wrote:
> On Fri, 17 Jun 2016 11:32:08 -0500
> Jeremy Linton <jeremy.linton@....com> wrote:
>
>
>>>> +
>>>> +	if (strcmp(token, "__u64") == 0) {
>>>> +		if (asprintf(&arg->atom.atom, "%zd", sizeof(__u64)) < 0)
>>>> +			goto out_free_atom;
>>>> +	} else if (strcmp(token, "__u32") == 0) {
>>>> +		if (asprintf(&arg->atom.atom, "%zd", sizeof(__u32)) < 0)
>>>> +			goto out_free_atom;
>>>
>>> What events are doing sizeof(__u64) and sizeof(__u32)?
>>>
>>> First, that's useless, as sizeof(__u64) will always be 8, and
>>> sizeof(__u32) will always be 4.
>>>
>>> What exactly is this fixing?
>>
>> It starts to fix things like:
>>
>> kmem:mm_page_alloc
>>     Warning: [kmem:mm_page_alloc] function sizeof not defined
>
> I don't see any sizeof() calls in my format files. And still, its
> useless to add sizeof() for __u64 and __u32 unless perhaps a type is a
> macro defined to that.
>
> Ah, this is arm64 (as I don't see it in x86).
>
> No the real fix is to nuke the sizeof(__u64) in the TP_printk(), it's
> useless because it will always be 8.

That is the simple case, initially I was going to just hand code some of 
the sizeofs in the kernel, but then I started noticing more complex 
cases, and why I RFCed this patch.

For example, on x64/xen there are fair number with sizeof(pXXval_t), 
IIRC I've also seen a fair number of sizeof(struct page *). Some, but I 
dont think all of these case be determined from the field sizes like 
this one:

[root@X tracing]# cat events/xen/xen_mmu_set_pte/format
name: xen_mmu_set_pte
ID: 45
format:
         field:unsigned short common_type;       offset:0;       size:2; 
signed:0;
         field:unsigned char common_flags;       offset:2;       size:1; 
signed:0;
         field:unsigned char common_preempt_count;       offset:3; 
  size:1; signed:0;
         field:int common_pid;   offset:4;       size:4; signed:1;

         field:pte_t * ptep;     offset:8;       size:8; signed:0;
         field:pteval_t pteval;  offset:16;      size:8; signed:0;

print fmt: "ptep %p pteval %0*llx (raw %0*llx)", REC->ptep, 
(int)sizeof(pteval_t) * 2, (unsigned long 
long)pte_val(native_make_pte(REC->pteval)), (int)sizeof(pteval_t) * 2, 
(unsigned long long)REC->pteval