From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Date: Mon, 24 Feb 2020 18:06:47 -0600
Subject: sfc: Replace zero-length array with flexible-array member
Patch-mainline: v5.7-rc1
Git-commit: 62f19142512885f4876928fcfbfa02838278de41
References: jsc#SLE-16683

The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Acked-by: Martin Habets <mhabets@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 drivers/net/ethernet/sfc/falcon/net_driver.h |    2 +-
 drivers/net/ethernet/sfc/net_driver.h        |    2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

--- a/drivers/net/ethernet/sfc/falcon/net_driver.h
+++ b/drivers/net/ethernet/sfc/falcon/net_driver.h
@@ -288,7 +288,7 @@ struct ef4_rx_buffer {
 struct ef4_rx_page_state {
 	dma_addr_t dma_addr;
 
-	unsigned int __pad[0] ____cacheline_aligned;
+	unsigned int __pad[] ____cacheline_aligned;
 };
 
 /**
--- a/drivers/net/ethernet/sfc/net_driver.h
+++ b/drivers/net/ethernet/sfc/net_driver.h
@@ -333,7 +333,7 @@ struct efx_rx_buffer {
 struct efx_rx_page_state {
 	dma_addr_t dma_addr;
 
-	unsigned int __pad[0] ____cacheline_aligned;
+	unsigned int __pad[] ____cacheline_aligned;
 };
 
 /**