linux-kernel - Re: [PATCH v2] PCI: rpaphp: Avoid a sometimes-uninitialized warning

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Message-ID: <20190627191837.GA111331@archlinux-epyc>
Date:   Thu, 27 Jun 2019 12:18:37 -0700
From:   Nathan Chancellor <natechancellor@...il.com>
To:     Tyrel Datwyler <tyreld@...ux.ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Nick Desaulniers <ndesaulniers@...gle.com>
Subject: Re: [PATCH v2] PCI: rpaphp: Avoid a sometimes-uninitialized warning

On Mon, Jun 03, 2019 at 03:11:58PM -0700, Nathan Chancellor wrote:
> 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++) {
>                     ^~~~~~~~~~~
> drivers/pci/hotplug/rpaphp_core.c:256:6: note: uninitialized use occurs
> here
>         if (fndit)
>             ^~~~~
> drivers/pci/hotplug/rpaphp_core.c:243:14: note: remove the condition if
> it is always true
>         for (j = 0; j < entries; j++) {
>                     ^~~~~~~~~~~
> drivers/pci/hotplug/rpaphp_core.c:233:14: note: initialize the variable
> 'fndit' to silence this warning
>         int j, fndit;
>                     ^
>                      = 0
> 
> 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.
> 
> Link: https://github.com/ClangBuiltLinux/linux/issues/504
> Fixes: 2fcf3ae508c2 ("hotplug/drc-info: Add code to search ibm,drc-info property")
> Suggested-by: Nick Desaulniers <ndesaulniers@...gle.com>
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
> 
> v1 -> v2:
> 
> * Eliminate fndit altogether by shuffling the sprintf call into the for
>   loop and changing the if conditional, as suggested by Nick.
> 
>  drivers/pci/hotplug/rpaphp_core.c | 18 +++++++-----------
>  1 file changed, 7 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/pci/hotplug/rpaphp_core.c b/drivers/pci/hotplug/rpaphp_core.c
> index bcd5d357ca23..c3899ee1db99 100644
> --- a/drivers/pci/hotplug/rpaphp_core.c
> +++ 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))) &&
> -- 
> 2.22.0.rc3
> 

Gentle ping, can someone pick this up?

Cheers,
Nathan