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

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Date:   Mon, 22 Jul 2019 14:05:12 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Nathan Chancellor <natechancellor@...il.com>,
        Tyrel Datwyler <tyreld@...ux.ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>
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

Nathan Chancellor <natechancellor@...il.com> writes:
> 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
>> 
>
> Hi all,
>
> Could someone please pick this up?

I'll take it.

I was expecting Bjorn to take it as a PCI patch, but I realise now that
I merged that code in the first place so may as well take this too.

I'll put it in my next branch once that opens next week.

cheers