[PATCH net 1/8] net: bcmgenet: fix 64-bit RTNL stats reading in ethtool on 32-bit systems

[Florian Fainelli <florian.fainelli@broadcom.com>]

When bcmgenet was converted to 64-bit statistics, STAT_RTNL members were
switched to point into struct rtnl_link_stats64, whose fields are 64-bit
(__u64) regardless of architecture.

However, bcmgenet_get_ethtool_stats() retained a legacy check:
  if (sizeof(unsigned long) != sizeof(u32) &&
      s->stat_sizeof == sizeof(unsigned long))

On 32-bit systems, sizeof(unsigned long) == sizeof(u32), causing this
condition to evaluate to false. As a result, 64-bit RTNL stats fields were
read via *(u32 *)p. On 32-bit Big-Endian systems (such as MIPS BE), this
reads the high 32 bits and returns 0 until the counter exceeds 4GB; on
32-bit Little-Endian systems (such as 32-bit ARM), the value is truncated
to 32 bits.

Fix this by checking if s->stat_sizeof == sizeof(u64) so 64-bit fields are
always read as 64-bit values.

Fixes: 59aa6e3072aa ("net: bcmgenet: switch to use 64bit statistics")
Assisted-by: LLM
Co-authored-by: Cursor <cursoragent@cursor.com>
Change-Id: I3e9f2f8d4fd136392148d6c0cd4eb40f7ccbe4ef
---
 drivers/net/ethernet/broadcom/genet/bcmgenet.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/genet/bcmgenet.c b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
index b916080f4ff1..7b089de9484e 100644
--- a/drivers/net/ethernet/broadcom/genet/bcmgenet.c
+++ b/drivers/net/ethernet/broadcom/genet/bcmgenet.c
@@ -1346,9 +1346,8 @@ static void bcmgenet_get_ethtool_stats(struct net_device *dev,
 				p = (char *)&stats64;
 
 			p += s->stat_offset;
-			if (sizeof(unsigned long) != sizeof(u32) &&
-				s->stat_sizeof == sizeof(unsigned long))
-				data[i] = *(unsigned long *)p;
+			if (s->stat_sizeof == sizeof(u64))
+				data[i] = *(u64 *)p;
 			else
 				data[i] = *(u32 *)p;
 		}
-- 
2.34.1