[PATCH] rocker: fix Wmaybe-uninitialized false-positive

[PATCH] rocker: fix Wmaybe-uninitialized false-positive

[Arnd Bergmann]

gcc-7 reports a warning that earlier versions did not have:

drivers/net/ethernet/rocker/rocker_ofdpa.c: In function 'ofdpa_port_stp_update':
arch/x86/include/asm/string_32.h:79:22: error: '*((void *)&prev_ctrls+4)' may be used uninitialized in this function [-Werror=maybe-uninitialized]
   *((short *)to + 2) = *((short *)from + 2);
   ~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
drivers/net/ethernet/rocker/rocker_ofdpa.c:2218:7: note: '*((void *)&prev_ctrls+4)' was declared here

This is clearly a variation of the warning about 'prev_state' that
was shut up using uninitialized_var().

We can slightly simplify the code and get rid of the warning by unconditionally
saving the prev_state and prev_ctrls variables. The inlined memcpy is not
particularly expensive here, as it just has to read five bytes from one or
two cache lines.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/net/ethernet/rocker/rocker_ofdpa.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/drivers/net/ethernet/rocker/rocker_ofdpa.c b/drivers/net/ethernet/rocker/rocker_ofdpa.c
index 7cd76b6b5cb9..2ae852454780 100644
--- a/drivers/net/ethernet/rocker/rocker_ofdpa.c
+++ b/drivers/net/ethernet/rocker/rocker_ofdpa.c
@@ -2216,18 +2216,15 @@ static int ofdpa_port_stp_update(struct ofdpa_port *ofdpa_port,
 {
 	bool want[OFDPA_CTRL_MAX] = { 0, };
 	bool prev_ctrls[OFDPA_CTRL_MAX];
-	u8 uninitialized_var(prev_state);
+	u8 prev_state;
 	int err;
 	int i;
 
-	if (switchdev_trans_ph_prepare(trans)) {
-		memcpy(prev_ctrls, ofdpa_port->ctrls, sizeof(prev_ctrls));
-		prev_state = ofdpa_port->stp_state;
-	}
-
-	if (ofdpa_port->stp_state == state)
+	prev_state = ofdpa_port->stp_state;
+	if (prev_state == state)
 		return 0;
 
+	memcpy(prev_ctrls, ofdpa_port->ctrls, sizeof(prev_ctrls));
 	ofdpa_port->stp_state = state;
 
 	switch (state) {
-- 
2.9.0

Re: [PATCH] rocker: fix Wmaybe-uninitialized false-positive

[David Miller]

From: Arnd Bergmann <arnd@arndb.de>
Date: Tue, 28 Mar 2017 16:11:18 +0200

> gcc-7 reports a warning that earlier versions did not have:
> 
> drivers/net/ethernet/rocker/rocker_ofdpa.c: In function 'ofdpa_port_stp_update':
> arch/x86/include/asm/string_32.h:79:22: error: '*((void *)&prev_ctrls+4)' may be used uninitialized in this function [-Werror=maybe-uninitialized]
>    *((short *)to + 2) = *((short *)from + 2);
>    ~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
> drivers/net/ethernet/rocker/rocker_ofdpa.c:2218:7: note: '*((void *)&prev_ctrls+4)' was declared here
> 
> This is clearly a variation of the warning about 'prev_state' that
> was shut up using uninitialized_var().
> 
> We can slightly simplify the code and get rid of the warning by unconditionally
> saving the prev_state and prev_ctrls variables. The inlined memcpy is not
> particularly expensive here, as it just has to read five bytes from one or
> two cache lines.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Applied, thank you.