linux-kernel - RE: [PATCH] blk-iocost: fix seq_printf compile type mismatch error

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Date:   Fri, 21 Jul 2023 08:05:59 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Tejun Heo' <tj@...nel.org>
CC:     Carlos Bilbao <carlos.bilbao@....com>,
        "josef@...icpanda.com" <josef@...icpanda.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        amd <amd@...alhost.localdomain>
Subject: RE: [PATCH] blk-iocost: fix seq_printf compile type mismatch error

From: Tejun Heo
> Sent: 20 July 2023 21:07
> 
> On Wed, Jul 19, 2023 at 08:57:32AM +0000, David Laight wrote:
> > From: Tejun Heo
> > > Sent: 17 July 2023 19:49
> > >
> > > On Mon, Jul 17, 2023 at 09:18:52AM -0500, Carlos Bilbao wrote:
> > > > From: amd <amd@...alhost.localdomain>
> > > >
> > > > Fix two type mismatch errors encountered while compiling blk-iocost.c with
> > > > GCC version 13.1.1 that involved constant operator WEIGHT_ONE. Cast the
> > > > result of the division operation to (unsigned int) to match the expected
> > > > format specifier %u in two seq_printf invocations.
> > >
> > > Can you detail the warnings? Was that on 32bit compiles?
> >
> > The problem is caused by gcc 13 changing the types of the
> > constants inside an enum to be all the same.
> >
> > The best fix is (probably) to replace all the enum used to
> > define unrelated constants with #defines.
> 
> Yeah, but then you end up without any way to read that value from outside
> the kernel for BPF, drgn or any other tools which use debug info. That
> actually matters.

Some of those constants (probably including the one that forces
the enum to 'long' are very boring.
I don't remember which one caused the change, but some were
similar to 'microseconds in a second'.

In any case it is enough to split the enum.
If you really need unrelated constants to be defined in an enum
them maybe use a separate enum for each.
Using (on one line):
	enum { name = constant };
may work best.

	David

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