linux-kernel - Re: [PATCH 4.19 011/106] PCI: rpaphp: Avoid a sometimes-uninitialized warning

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Message-ID: <20191008094554.GB608@amd>
Date:   Tue, 8 Oct 2019 11:45:54 +0200
From:   Pavel Machek <pavel@...x.de>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Nathan Chancellor <natechancellor@...il.com>,
        Tyrel Datwyler <tyreld@...ux.ibm.com>,
        Joel Savitz <jsavitz@...hat.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 011/106] PCI: rpaphp: Avoid a
 sometimes-uninitialized warning

Hi!

> From: Nathan Chancellor <natechancellor@...il.com>
> 
> [ Upstream commit 0df3e42167caaf9f8c7b64de3da40a459979afe8 ]
> 
> When building with -Wsometimes-uninitialized, clang warns:
> 
> drivers/pci/hotplug/rpaphp_core.c:243:14: warning: variable 'fndit' is
> used uninitialized whenever 'for' loop exits because its condition is
> false [-Wsometimes-uninitialized]
>         for (j = 0; j < entries; j++) {
>                     ^~~~~~~~~~~
...
> fndit is only used to gate a sprintf call, which can be moved into the
> loop to simplify the code and eliminate the local variable, which will
> fix this warning.

Well, you fixed the warning, but the code is still buggy:

> +++ b/drivers/pci/hotplug/rpaphp_core.c
> @@ -230,7 +230,7 @@ static int rpaphp_check_drc_props_v2(struct device_node *dn, char *drc_name,
>  	struct of_drc_info drc;
>  	const __be32 *value;
>  	char cell_drc_name[MAX_DRC_NAME_LEN];
> -	int j, fndit;
> +	int j;
>  
>  	info = of_find_property(dn->parent, "ibm,drc-info", NULL);
>  	if (info == NULL)
> @@ -245,17 +245,13 @@ static int rpaphp_check_drc_props_v2(struct device_node *dn, char *drc_name,
>  
>  		/* Should now know end of current entry */
>  
> -		if (my_index > drc.last_drc_index)
> -			continue;
> -
> -		fndit = 1;
> -		break;
> +		/* Found it */
> +		if (my_index <= drc.last_drc_index) {
> +			sprintf(cell_drc_name, "%s%d", drc.drc_name_prefix,
> +				my_index);
> +			break;
> +		}
>  	}
> -	/* Found it */
> -
> -	if (fndit)
> -		sprintf(cell_drc_name, "%s%d", drc.drc_name_prefix, 
> -			my_index);
>  
>  	if (((drc_name == NULL) ||
>  	     (drc_name && !strcmp(drc_name, cell_drc_name))) &&

In case we do not find it, cell_drc_name is not initialized, yet we
use it in strcmp(). Same bug exists in the mainline.

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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