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

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Message-ID: <20190802001102.GG151852@google.com>
Date:   Thu, 1 Aug 2019 19:11:02 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Michael Ellerman <mpe@...erman.id.au>
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

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.

Bjorn