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

Jeremy Linton
2016-06-17T18:57:47Z

On 06/17/2016 11:50 AM, Steven Rostedt wrote:
> On Fri, 17 Jun 2016 11:32:08 -0500
> Jeremy Linton <jeremy.linton@arm.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