linux-kernel - Re: [alobakin:pfcp 11/19] include/linux/bitmap.h:642:17: warning: array subscript [1, 1024] is outside array bounds of 'long unsigned int[1]'

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Date:   Tue, 7 Nov 2023 05:22:20 -0800
From:   Yury Norov <yury.norov@...il.com>
To:     Alexander Lobakin <aleksander.lobakin@...el.com>
Cc:     Alexander Potapenko <glider@...gle.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Syed Nayyar Waris <syednwaris@...il.com>,
        kernel test robot <lkp@...el.com>,
        oe-kbuild-all@...ts.linux.dev,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [alobakin:pfcp 11/19] include/linux/bitmap.h:642:17: warning:
 array subscript [1, 1024] is outside array bounds of 'long unsigned int[1]'

On Mon, Nov 06, 2023 at 05:31:34PM +0100, Alexander Lobakin wrote:
> BTW, I have this in my inbox:
> 
> From: Kernel Test Robot <lkp@...el.com>
> Date: Tue, 17 Oct 2023 08:14:51 +0800
> 
> > tree:   https://github.com/alobakin/linux pfcp
> > head:   9183a3eb639912169a3d3e2be4f25556b465919b
> > commit: c8a652cdcc0964510f108726b3da0784d1bc0cd2 [11/19] bitmap: make bitmap_{get,set}_value8() use bitmap_{read,write}()
> 
> So it happened after I converted bitmap_{get,set}_value8() so that they
> use bitmap_{read,write}().
> 
> > config: x86_64-randconfig-004-20231017 (https://download.01.org/0day-ci/archive/20231017/202310170708.fJzLlgDM-lkp@intel.com/config)
> > compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
> > reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231017/202310170708.fJzLlgDM-lkp@intel.com/reproduce)

[...]
 
> >      643 |  map[index + 1] |= (value >> space);
> >          |                 ^~
> >    In file included from include/linux/kasan-checks.h:5,
> >                     from include/asm-generic/rwonce.h:26,
> >                     from ./arch/x86/include/generated/asm/rwonce.h:1,
> >                     from include/linux/compiler.h:246,
> >                     from include/linux/build_bug.h:5,
> >                     from include/linux/bits.h:21,
> >                     from include/linux/ioport.h:13,
> >                     from include/linux/acpi.h:12,
> >                     from drivers/gpio/gpio-pca953x.c:11:
> >    drivers/gpio/gpio-pca953x.c:1032:17: note: while referencing 'val'

It looks like a gcc-9 false-positive. I tried gcc-12 and gcc-13, and
they both looks OK. Below is the fix that works for me.

Can you please test the following patch and add it to your series?

Thanks,
        Yury

>From 2a883221ddbd18796ddef0125e9e3022a56edd7b Mon Sep 17 00:00:00 2001
From: Yury Norov <yury.norov@...il.com>
Date: Tue, 7 Nov 2023 05:05:17 -0800
Subject: [PATCH] bitmap: suppress false-positive -Warray-bounds in
 bitmap_{read,write}

bitmap_{read,write} conditionally accesses map[index + 1], carefully
checking before that it's a safe dereference. But still, gcc-9 emits
-Warray-bounds.

Gcc-12 and gcc-13 are both OK with this code. So fix it for gcc-9 with
OPTIMIZER_HIDE_VAR().

Reported-by: Alexander Lobakin <aleksander.lobakin@...el.com>
Reported-by: kernel test robot <lkp@...el.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202310170708.fJzLlgDM-lkp@intel.com/
Signed-off-by: Yury Norov <yury.norov@...il.com>
---
 include/linux/bitmap.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 945a680816cc..0b1a07ff1080 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -592,6 +592,11 @@ static inline unsigned long bitmap_read(const unsigned long *map,
 	if (unlikely(!nbits || nbits > BITS_PER_LONG))
 		return 0;
 
+#if CONFIG_GCC_VERSION < 100000
+	/* Suppress gcc-9 false-positive -Warray-bounds */
+	OPTIMIZER_HIDE_VAR(map);
+#endif
+
 	if (space >= nbits)
 		return (map[index] >> offset) & BITMAP_LAST_WORD_MASK(nbits);
 
@@ -634,6 +639,11 @@ static inline void bitmap_write(unsigned long *map, unsigned long value,
 	fit = space >= nbits;
 	index = BIT_WORD(start);
 
+#if CONFIG_GCC_VERSION < 100000
+	/* Suppress gcc-9 false-positive -Warray-bounds */
+	OPTIMIZER_HIDE_VAR(map);
+#endif
+
 	map[index] &= (fit ? (~(mask << offset)) : ~BITMAP_FIRST_WORD_MASK(start));
 	map[index] |= value << offset;
 	if (fit)
-- 
2.39.2