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