linux-kernel - RE: ftrace histogram sorting broken on BE architecures

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Date:   Tue, 17 Dec 2019 10:05:57 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Steven Rostedt' <rostedt@...dmis.org>
CC:     'Tom Zanussi' <zanussi@...nel.org>,
        Sven Schnelle <svens@...ckframe.org>,
        "linux-trace-devel@...r.kernel.org" 
        <linux-trace-devel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: RE: ftrace histogram sorting broken on BE architecures

From: Steven Rostedt
> Sent: 16 December 2019 18:29
> On Mon, 16 Dec 2019 17:06:50 +0000
> David Laight <David.Laight@...LAB.COM> wrote:
> 
> > > Where original_val_a could be a byte, short, int, long or long long.
> >
> > I'd sort of guessed that, but then the pointer type passed to tracing_map_cmp_##type()
> > will always be 'u64 *' (since the field the address is taken of must be that type).
> > Then the (u64 *) casts are no longer needed.
> >
> > Possibly you can just pass the u64 values to:
> > tracing_map_cmp_##type(type a, type b)
> > {
> > 	return a > b ? 1 : a < b ? -1 : 0;
> > }
> >
> > The high bit masking and sign extension is then implicit in the call.
> 
> But these are used to pass into a compare function that takes compare
> functions that are something other than numbers. They can be pointers
> to strings.

In that case I think I'd embed the u64 inside a structure and pass the structure
address to the compare function.

	David

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