linux-kernel - [PATCH] arm:fix negation of -2147483648 warning with UBSASN

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Message-Id: <1507804858-10205-1-git-send-email-manjeet.p@samsung.com>
Date:   Thu, 12 Oct 2017 16:10:58 +0530
From:   Manjeet Pawar <manjeet.p@...sung.com>
To:     linux@....linux.org.uk, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Cc:     pankaj.m@...sung.com, a.sahrawat@...sung.com,
        lalit.mohan@...sung.com, Rohit Thapliyal <r.thapliyal@...sung.com>,
        Manjeet Pawar <manjeet.p@...sung.com>
Subject: [PATCH] arm:fix negation of -2147483648 warning with UBSASN

From: Rohit Thapliyal <r.thapliyal@...sung.com>

Using gcc-6 and UBSAN enabled, we get the following warning:

=========================================================
[1-1.4604] UBSAN: Undefined behaviour in ./arch/arm/include/asm/bitops.h:296:17
[1-1.4604] negation of -2147483648 cannot be represented in type 'int':
[1-1.4605] CPU: 1 PID: 189 Comm: sync Tainted: GO 4.1.10 #1 PPID: 166 PComm: init
[1-1.4605] SCHED_NORMAL (p:120, static_p:120, normal_p:120, rt_p:0)
[1-1.4605] Backtrace:
[1-1.4605] [<c0016050>] (dump_backtrace) from [<c0016fac>] (show_stack+0x18/0x20)
[1-1.4605]  r7:c098196c r6:00000000 r5:60040093 r4:c0a177f4
[1-1.4605] [<c0016f94>] (show_stack) from [<c06f36d8>] (dump_stack+0xf4/0x148)
[1-1.4605] [<c06f35e4>] (dump_stack) from [<c03b8b94>] (ubsan_epilogue+0x14/0x54)
[1-1.4605]  r10:00000101 r9:00000120 r8:00000100 r7:00001000 r6:80000000 r5:c0a18b00
[1-1.4605]  r4:d8099c00
[1-1.4605] [<c03b8b80>] (ubsan_epilogue) from [<c03b941c>] (__ubsan_handle_negate_overflow+0x88/0x90)
[1-1.4605]  r5:c0a18b00 r4:c098148c
[1-1.4605] [<c03b9394>] (__ubsan_handle_negate_overflow) from [<c03823c4>] (radix_tree_next_chunk+0x380/0x470)
[1-1.4605]  r6:e1b88d20 r5:00000006 r4:00000020
[1-1.4606] [<c0382044>] (radix_tree_next_chunk) from [<c0158f10>] (find_get_pages_tag+0x158/0x1e8)
[1-1.4606]  r10:00000004 r9:0000000e r8:00000101 r7:ffffffff r6:00000000 r5:e1b91cb4
[1-1.4606]  r4:00000001
[1-1.4606] [<c0158db8>] (find_get_pages_tag) from [<c016e160>] (pagevec_lookup_tag+0x30/0x3c)
[1-1.4606]  r10:0000000e r9:27f662e4 r8:00000000 r7:ffffffff r6:e50da320 r5:d8099d60
=========================================================

In order to remove these warnings, it seems harmless to modify
the signed ints with unsigned long as a fix of negation of -2147483648 in signed int.

Signed-off-by: Rohit Thapliyal <r.thapliyal@...sung.com>
Signed-off-by: Manjeet Pawar <manjeet.p@...sung.com>
---
 arch/arm/include/asm/bitops.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/arm/include/asm/bitops.h b/arch/arm/include/asm/bitops.h
index 5638099..95028db 100644
--- a/arch/arm/include/asm/bitops.h
+++ b/arch/arm/include/asm/bitops.h
@@ -222,7 +222,7 @@ extern int _find_next_bit_be(const unsigned long *p, int size, int offset);
 
 #else
 
-static inline int constant_fls(int x)
+static inline int constant_fls(unsigned long x)
 {
 	int r = 32;
 
@@ -270,7 +270,7 @@ static inline unsigned int __clz(unsigned int x)
  * fls() returns zero if the input is zero, otherwise returns the bit
  * position of the last set bit, where the LSB is 1 and MSB is 32.
  */
-static inline int fls(int x)
+static inline int fls(unsigned long x)
 {
 	if (__builtin_constant_p(x))
 	       return constant_fls(x);
@@ -291,7 +291,7 @@ static inline unsigned long __fls(unsigned long x)
  * ffs() returns zero if the input was zero, otherwise returns the bit
  * position of the first set bit, where the LSB is 1 and MSB is 32.
  */
-static inline int ffs(int x)
+static inline int ffs(unsigned long x)
 {
 	return fls(x & -x);
 }
-- 
1.9.1