The patch titled
Subject: gcc: disable '-Warray-bounds' for gcc-9
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
gcc-disable-warray-bounds-for-gcc-9.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/gcc-disable-warray-bounds-for-gcc-9.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Yury Norov <yury.norov@xxxxxxxxx>
Subject: gcc: disable '-Warray-bounds' for gcc-9
Date: Wed, 22 May 2024 15:58:30 -0700
'-Warray-bounds' is already disabled for gcc-10+. Now that we've merged
bitmap_{read,write), I see the following error when building the kernel
with gcc-9.4 (Ubuntu 20.04.4 LTS) for x86_64 allmodconfig:
drivers/pinctrl/pinctrl-cy8c95x0.c: In function `cy8c95x0_read_regs_mask.isra.0':
include/linux/bitmap.h:756:18: error: array subscript [1, 288230376151711744] is outside array bounds of `long unsigned int[1]' [-Werror=array-bounds]
756 | value_high = map[index + 1] & BITMAP_LAST_WORD_MASK(start + nbits);
| ~~~^~~~~~~~~~~
The immediate reason is that the commit b44759705f7d ("bitmap: make
bitmap_{get,set}_value8() use bitmap_{read,write}()") switched the
bitmap_get_value8() to an alias of bitmap_read(); the same for 'set'.
Now; the code that triggers Warray-bounds, calls the function like this:
#define MAX_BANK 8
#define BANK_SZ 8
#define MAX_LINE (MAX_BANK * BANK_SZ)
DECLARE_BITMAP(tval, MAX_LINE); // 64-bit map: unsigned long tval[1]
read_val |= bitmap_get_value8(tval, i * BANK_SZ) & ~bits;
bitmap_read() is implemented such that it may conditionally dereference a
pointer beyond the boundary like this:
unsigned long offset = start % BITS_PER_LONG;
unsigned long space = BITS_PER_LONG - offset;
if (space >= nbits)
return (map[index] >> offset) & BITMAP_LAST_WORD_MASK(nbits);
value_low = map[index] & BITMAP_FIRST_WORD_MASK(start);
value_high = map[index + 1] & BITMAP_LAST_WORD_MASK(start + nbits);
return (value_low >> offset) | (value_high << space);
In case of bitmap_get_value8(), it's impossible to violate the boundary
because 'space >= nbits' is never the true for byte-aligned 8-bit access.
So, this is clearly a false-positive.
The same type of false-positives break my allmodconfig build in many
places. gcc-8, is clear, however.
Link: https://lkml.kernel.org/r/20240522225830.1201778-1-yury.norov@xxxxxxxxx
Signed-off-by: Yury Norov <yury.norov@xxxxxxxxx>
Cc: Alexander Lobakin <aleksander.lobakin@xxxxxxxxx>
Cc: David S. Miller <davem@xxxxxxxxxxxxx>
Cc: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
Cc: Nhat Pham <nphamcs@xxxxxxxxx>
Cc: Petr Mladek <pmladek@xxxxxxxx>
Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
Cc: Yoann Congal <yoann.congal@xxxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
init/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/init/Kconfig~gcc-disable-warray-bounds-for-gcc-9
+++ a/init/Kconfig
@@ -883,7 +883,7 @@ config GCC10_NO_ARRAY_BOUNDS
config CC_NO_ARRAY_BOUNDS
bool
- default y if CC_IS_GCC && GCC_VERSION >= 100000 && GCC10_NO_ARRAY_BOUNDS
+ default y if CC_IS_GCC && GCC_VERSION >= 90000 && GCC10_NO_ARRAY_BOUNDS
# Currently, disable -Wstringop-overflow for GCC globally.
config GCC_NO_STRINGOP_OVERFLOW
_
Patches currently in -mm which might be from yury.norov@xxxxxxxxx are
gcc-disable-warray-bounds-for-gcc-9.patch
