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

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Message-ID: <87v9vfkb5n.fsf@concordia.ellerman.id.au>
Date:   Fri, 02 Aug 2019 22:24:36 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Nathan Chancellor <natechancellor@...il.com>,
        Tyrel Datwyler <tyreld@...ux.ibm.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>, 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

Bjorn Helgaas <helgaas@...nel.org> writes:
> On Mon, Jul 22, 2019 at 02:05:12PM +1000, Michael Ellerman wrote:
>> 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.
>
> Sorry, I should have done something with this.  Did you take it,
> Michael?  I don't see it in -next and haven't figured out where to
> look in your git tree, so I can't tell.  Just let me know either way
> so I know whether to drop this or apply it.

Yes I have it in my next-test, which will eventually become my next when
I get time to rebase it, test and push etc:

https://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux.git/log/?h=next-test

So no further action required on your part.

cheers