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

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Date:	Fri, 17 Jun 2016 12:50:42 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jeremy Linton <jeremy.linton@....com>
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 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.

-- Steve


> 
> or:
> 
> # perf stat -e kvm:kvm_arm_set_regset -- true
>    Warning: [kvm:kvm_arm_set_regset] function sizeof not defined
>    Warning: Error: expected type 5 but read 0
> *** Error in `perf': double free or corruption (fasttop): 
> 0x00000000303f5930 ***
> 
> There is a RH bug about it (and the "~" operator, which has been fixed) 
> here: https://bugzilla.redhat.com/show_bug.cgi?id=1298229
> 
> Thanks for taking a look at this,