linux-kernel - Re: linux-next: build failure after merge of the kspp tree

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Message-Id: <20220126093538.893fb44a7cb0a7cd840c7fdb@kernel.org>
Date:   Wed, 26 Jan 2022 09:35:38 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        Beau Belgrave <beaub@...ux.microsoft.com>
Subject: Re: linux-next: build failure after merge of the kspp tree

Hi Steve,
(Ccing Beau)

On Tue, 25 Jan 2022 17:21:14 -0500
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Tue, 25 Jan 2022 14:07:14 -0800
> Kees Cook <keescook@...omium.org> wrote:
> 
> > > The tstruct is the TP_STRUCT__entry() and for each __rel_dynamic_array() or
> > > __dynamic_array(), the __data_size gets updated and saved into the
> > > __data_offsets that holds where each item is.
> > > 
> > > The rel versions sets the offset from its location to the data, where as
> > > the non rel versions sets the offset from the beginning of the event to the
> > > data.  
> > 
> > Could this just be
> > 
> > #define __get_rel_dynamic_array(field) \
> > 	((void *)(&__entry->data[__entry->__rel_loc_##field & 0xffff])
> > 
> > ?
> 
> This is currently user space defined. But since the only user of the rel_*
> version hasn't been upstreamed yet, we could change it. But it also
> requires changing libtraceevent as it depends on this code too.

I think Kees' idea seems better. If you and Beau are good, I will update
the macros for __rel_loc. (This requires to change some user-space
application which Beau is making too.)

> 
> I'm surprised that it doesn't break with the __get_dynamic_array()
> versions, or is that because it's based off of __entry?

I think so. Gcc seems to check the size of the data structure where the
original base address points.

Thank you,

> 
> -- Steve


-- 
Masami Hiramatsu <mhiramat@...nel.org>