linux-kernel - [PATCH 4.9 15/47] parisc: avoid a warning on u8 cast for cmpxchg on u8 pointers

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Date:   Thu, 15 Apr 2021 16:47:07 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Liam Beguin <liambeguin@...il.com>,
        Helge Deller <deller@....de>, Gao Xiang <hsiangkao@...hat.com>
Subject: [PATCH 4.9 15/47] parisc: avoid a warning on u8 cast for cmpxchg on u8 pointers

From: Gao Xiang <hsiangkao@...hat.com>

commit 4d752e5af63753ab5140fc282929b98eaa4bd12e upstream.

commit b344d6a83d01 ("parisc: add support for cmpxchg on u8 pointers")
can generate a sparse warning ("cast truncates bits from constant
value"), which has been reported several times [1] [2] [3].

The original code worked as expected, but anyway, let silence such
sparse warning as what others did [4].

[1] https://lore.kernel.org/r/202104061220.nRMBwCXw-lkp@intel.com
[2] https://lore.kernel.org/r/202012291914.T5Agcn99-lkp@intel.com
[3] https://lore.kernel.org/r/202008210829.KVwn7Xeh%25lkp@intel.com
[4] https://lore.kernel.org/r/20210315131512.133720-2-jacopo+renesas@jmondi.org
Cc: Liam Beguin <liambeguin@...il.com>
Cc: Helge Deller <deller@....de>
Cc: stable@...r.kernel.org # v5.8+
Signed-off-by: Gao Xiang <hsiangkao@...hat.com>
Signed-off-by: Helge Deller <deller@....de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/parisc/include/asm/cmpxchg.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/parisc/include/asm/cmpxchg.h
+++ b/arch/parisc/include/asm/cmpxchg.h
@@ -71,7 +71,7 @@ __cmpxchg(volatile void *ptr, unsigned l
 #endif
 	case 4: return __cmpxchg_u32((unsigned int *)ptr,
 				     (unsigned int)old, (unsigned int)new_);
-	case 1: return __cmpxchg_u8((u8 *)ptr, (u8)old, (u8)new_);
+	case 1: return __cmpxchg_u8((u8 *)ptr, old & 0xff, new_ & 0xff);
 	}
 	__cmpxchg_called_with_bad_pointer();
 	return old;