linux-kernel - Re: [PATCH v2] coccinelle: assign signed result to unsigned variable

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Date:	Wed, 30 Sep 2015 23:51:43 +0200 (CEST)
From:	Julia Lawall <julia.lawall@...6.fr>
To:	Andrzej Hajda <a.hajda@...sung.com>
cc:	Julia Lawall <julia.lawall@...6.fr>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Gilles Muller <Gilles.Muller@...6.fr>,
	Michal Marek <mmarek@...e.com>,
	Nicolas Palix <nicolas.palix@...g.fr>,
	kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org,
	cocci@...teme.lip6.fr, elfring@...rs.sourceforge.net
Subject: Re: [PATCH v2] coccinelle: assign signed result to unsigned
 variable



On Mon, 28 Sep 2015, Andrzej Hajda wrote:

> On 09/28/2015 01:32 PM, Julia Lawall wrote:
> >
> > On Mon, 28 Sep 2015, Andrzej Hajda wrote:
> >
> >> Assigning signed function result to unsigned variable can indicate error.
> >> To decrease number of false positives patch looks if after assignment
> >> there is also check for negative values of the result.
> >>
> >> Signed-off-by: Andrzej Hajda <a.hajda@...sung.com>
> >> ---
> >> Hi Julia,
> >>
> >> Thanks for the hint. Now it looks much better.
> >> Summarizing this patch has found 20 problems and has 22 false positives [1][2].
> > Do you have some examples of the false positives?
> ./drivers/acpi/acpica/nsarguments.c:130:1: WARNING: Assigning signed result to
> unsigned variable: required_param_count = METHOD_GET_ARG_COUNT(...)
> ./drivers/char/agp/intel-gtt.c:361:3: WARNING: Assigning signed result to
> unsigned variable: stolen_size = KB(...)
> ./drivers/char/agp/intel-gtt.c:364:3: WARNING: Assigning signed result to
> unsigned variable: stolen_size = MB(...)
> ./drivers/char/agp/intel-gtt.c:367:3: WARNING: Assigning signed result to
> unsigned variable: stolen_size = MB(...)
> ./drivers/char/agp/intel-gtt.c:382:3: WARNING: Assigning signed result to
> unsigned variable: stolen_size = MB(...)
> ./drivers/char/agp/intel-gtt.c:385:3: WARNING: Assigning signed result to
> unsigned variable: stolen_size = MB(...)
> ./drivers/char/agp/intel-gtt.c:388:3: WARNING: Assigning signed result to
> unsigned variable: stolen_size = MB(...)
> ./drivers/char/agp/intel-gtt.c:391:3: WARNING: Assigning signed result to
> unsigned variable: stolen_size = MB(...)
> ./drivers/char/agp/intel-gtt.c:394:3: WARNING: Assigning signed result to
> unsigned variable: stolen_size = MB(...)
> ./drivers/char/agp/intel-gtt.c:397:3: WARNING: Assigning signed result to
> unsigned variable: stolen_size = MB(...)
> ./drivers/char/agp/intel-gtt.c:400:3: WARNING: Assigning signed result to
> unsigned variable: stolen_size = MB(...)
> ./drivers/char/agp/intel-gtt.c:403:3: WARNING: Assigning signed result to
> unsigned variable: stolen_size = MB(...)
> ./drivers/char/agp/intel-gtt.c:406:3: WARNING: Assigning signed result to
> unsigned variable: stolen_size = MB(...)
> ./drivers/char/agp/intel-gtt.c:409:3: WARNING: Assigning signed result to
> unsigned variable: stolen_size = MB(...)
> ./drivers/char/agp/intel-gtt.c:412:3: WARNING: Assigning signed result to
> unsigned variable: stolen_size = MB(...)
> ./drivers/char/agp/intel-gtt.c:415:3: WARNING: Assigning signed result to
> unsigned variable: stolen_size = MB(...)
> ./drivers/char/agp/intel-gtt.c:418:3: WARNING: Assigning signed result to
> unsigned variable: stolen_size = MB(...)
> ./drivers/input/touchscreen/cyttsp4_core.c:967:1: WARNING: Assigning signed
> result to unsigned variable: num_cur_tch = GET_NUM_TOUCHES(...)
> ./drivers/pinctrl/freescale/pinctrl-imx.c:648:2: WARNING: Assigning signed
> result to unsigned variable: nfuncs = of_get_child_count(...)
> ./fs/btrfs/file.c:1572:2: WARNING: Assigning signed result to unsigned variable:
> copied = btrfs_copy_from_user(...)
> ./fs/xfs/libxfs/xfs_inode_fork.c:541:2: WARNING: Assigning signed result to
> unsigned variable: new_size = XFS_BMAP_BROOT_SPACE_CALC(...)
> 
> As you see most of them are macros, of_get_child_count and btrfs_copy_from_user
> return int but always non-negative.

OK, perhaps we could just live with them...

julia
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