| Message ID | 1453903507-3427225-9-git-send-email-arnd@arndb.de |
|---|---|
| State | New |
| Headers | show |
| Series | None | expand |
Arnd Bergmann <arnd@arndb.de> writes: > The nb8800_poll() function initializes the 'next' variable in the > loop looking for new input data. We know this will be called at > least once because 'budget' is a guaranteed to be a positive number > when we enter the function, but the compiler doesn't know that > and warns when the variable is used later: > > drivers/net/ethernet/aurora/nb8800.c: In function 'nb8800_poll': > drivers/net/ethernet/aurora/nb8800.c:350:21: warning: 'next' may be used uninitialized in this function [-Wmaybe-uninitialized] Which gcc version is this? 4.9 doesn't warn here, presumably because it's clever enough to notice that the offending use of 'next' is under a condition that can only be true if the first one was. Of course fixing the code so older compilers don't warn is a good idea. > Changing the 'while() {}' loop to 'do {} while()' makes it obvious > to the compiler what is going on so it no longer warns. > > Signed-off-by: Arnd Bergmann <arnd@arndb.de> Acked-by: Mans Rullgard <mans@mansr.com> > --- > drivers/net/ethernet/aurora/nb8800.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/net/ethernet/aurora/nb8800.c b/drivers/net/ethernet/aurora/nb8800.c > index ecc4a334c507..f71ab2647a3b 100644 > --- a/drivers/net/ethernet/aurora/nb8800.c > +++ b/drivers/net/ethernet/aurora/nb8800.c > @@ -302,7 +302,7 @@ static int nb8800_poll(struct napi_struct *napi, int budget) > nb8800_tx_done(dev); > > again: > - while (work < budget) { > + do { > struct nb8800_rx_buf *rxb; > unsigned int len; > > @@ -330,7 +330,7 @@ again: > rxd->report = 0; > last = next; > work++; > - } > + } while (work < budget); > > if (work) { > priv->rx_descs[last].desc.config |= DESC_EOC; > -- > 2.7.0 > -- Måns Rullgård
On Wednesday 27 January 2016 14:13:16 Måns Rullgård wrote: > Arnd Bergmann <arnd@arndb.de> writes: > > > The nb8800_poll() function initializes the 'next' variable in the > > loop looking for new input data. We know this will be called at > > least once because 'budget' is a guaranteed to be a positive number > > when we enter the function, but the compiler doesn't know that > > and warns when the variable is used later: > > > > drivers/net/ethernet/aurora/nb8800.c: In function 'nb8800_poll': > > drivers/net/ethernet/aurora/nb8800.c:350:21: warning: 'next' may be used uninitialized in this function [-Wmaybe-uninitialized] > > Which gcc version is this? 4.9 doesn't warn here, presumably because > it's clever enough to notice that the offending use of 'next' is under a > condition that can only be true if the first one was. Of course fixing > the code so older compilers don't warn is a good idea. This was with gcc-5.2.1, but possibly in an unusual kernel configuration. The only time I see it in my logs was with CONFIG_ARCH_IXP4XX=y, which has its own mach/io.h and other headers that sometimes override generic functions with a more elaborate version. I have another patch for ixp4xx that simplifies its mach/io.h in order to get rid of other false 'uninitialized use' warnings, but this one still shows up with that other patch. > > Changing the 'while() {}' loop to 'do {} while()' makes it obvious > > to the compiler what is going on so it no longer warns. > > > > Signed-off-by: Arnd Bergmann <arnd@arndb.de> > > Acked-by: Mans Rullgard <mans@mansr.com> Thanks, Arnd
diff --git a/drivers/net/ethernet/aurora/nb8800.c b/drivers/net/ethernet/aurora/nb8800.c index ecc4a334c507..f71ab2647a3b 100644 --- a/drivers/net/ethernet/aurora/nb8800.c +++ b/drivers/net/ethernet/aurora/nb8800.c @@ -302,7 +302,7 @@ static int nb8800_poll(struct napi_struct *napi, int budget) nb8800_tx_done(dev); again: - while (work < budget) { + do { struct nb8800_rx_buf *rxb; unsigned int len; @@ -330,7 +330,7 @@ again: rxd->report = 0; last = next; work++; - } + } while (work < budget); if (work) { priv->rx_descs[last].desc.config |= DESC_EOC;
The nb8800_poll() function initializes the 'next' variable in the loop looking for new input data. We know this will be called at least once because 'budget' is a guaranteed to be a positive number when we enter the function, but the compiler doesn't know that and warns when the variable is used later: drivers/net/ethernet/aurora/nb8800.c: In function 'nb8800_poll': drivers/net/ethernet/aurora/nb8800.c:350:21: warning: 'next' may be used uninitialized in this function [-Wmaybe-uninitialized] Changing the 'while() {}' loop to 'do {} while()' makes it obvious to the compiler what is going on so it no longer warns. Signed-off-by: Arnd Bergmann <arnd@arndb.de> --- drivers/net/ethernet/aurora/nb8800.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) -- 2.7.0