[PATCH] am65-cpsw: avoid null pointer arithmetic

From: Arnd Bergmann <arnd@arndb.de>

clang warns about arithmetic on NULL pointers:

drivers/net/ethernet/ti/am65-cpsw-ethtool.c:71:2: error: performing pointer subtraction with a null pointer has undefined behavior [-Werror,-Wnull-pointer-subtraction]
        AM65_CPSW_REGDUMP_REC(AM65_CPSW_REGDUMP_MOD_NUSS, 0x0, 0x1c),
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/net/ethernet/ti/am65-cpsw-ethtool.c:64:29: note: expanded from macro 'AM65_CPSW_REGDUMP_REC'
        .hdr.len = (((u32 *)(end)) - ((u32 *)(start)) + 1) * sizeof(u32) * 2 + \
                                   ^ ~~~~~~~~~~~~~~~~

The expression here is easily changed to a calculation based on integers
that is no less readable.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/net/ethernet/ti/am65-cpsw-ethtool.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/ti/am65-cpsw-ethtool.c b/drivers/net/ethernet/ti/am65-cpsw-ethtool.c
index 6e4d4f9e32e0..b05de9b61ad6 100644
--- a/drivers/net/ethernet/ti/am65-cpsw-ethtool.c
+++ b/drivers/net/ethernet/ti/am65-cpsw-ethtool.c

@@ -61,7 +61,7 @@ struct am65_cpsw_regdump_item {
 
 #define AM65_CPSW_REGDUMP_REC(mod, start, end) { \
 	.hdr.module_id = (mod), \
-	.hdr.len = (((u32 *)(end)) - ((u32 *)(start)) + 1) * sizeof(u32) * 2 + \
+	.hdr.len = (end + 4 - start) * 2 + \
 		   sizeof(struct am65_cpsw_regdump_hdr), \
 	.start_ofs = (start), \
 	.end_ofs = end, \

-- 
2.29.2

Hello:

This patch was applied to netdev/net-next.git (refs/heads/master):

On Mon, 27 Sep 2021 11:37:57 +0200 you wrote:

From: Arnd Bergmann <arnd@arndb.de>

clang warns about arithmetic on NULL pointers:

drivers/net/ethernet/ti/am65-cpsw-ethtool.c:71:2: error: performing pointer subtraction with a null pointer has undefined behavior [-Werror,-Wnull-pointer-subtraction]
        AM65_CPSW_REGDUMP_REC(AM65_CPSW_REGDUMP_MOD_NUSS, 0x0, 0x1c),
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/net/ethernet/ti/am65-cpsw-ethtool.c:64:29: note: expanded from macro 'AM65_CPSW_REGDUMP_REC'
        .hdr.len = (((u32 *)(end)) - ((u32 *)(start)) + 1) * sizeof(u32) * 2 + \
                                   ^ ~~~~~~~~~~~~~~~~

[...]

Here is the summary with links:
  - am65-cpsw: avoid null pointer arithmetic
    https://git.kernel.org/netdev/net-next/c/861f40fa0edf

You are awesome, thank you!
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