From 8e5bd4eadd01ea0c47f3a1c798815849f813a700 Mon Sep 17 00:00:00 2001 From: Yury Norov Date: Wed, 22 May 2024 15:58:30 -0700 Subject: [PATCH] gcc: disable '-Warray-bounds' for gcc-9 '-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@gmail.com Fixes: b44759705f7d ("bitmap: make bitmap_{get,set}_value8() use bitmap_{read,write}()") Signed-off-by: Yury Norov Cc: Alexander Lobakin Cc: David S. Miller Cc: Gustavo A. R. Silva Cc: Masahiro Yamada Cc: Nhat Pham Cc: Petr Mladek Cc: Randy Dunlap Cc: Vincent Guittot Cc: Yoann Congal Cc: Arnd Bergmann Signed-off-by: Andrew Morton --- init/Kconfig | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/init/Kconfig b/init/Kconfig index 72404c1f2157..febdea2afc3b 100644 --- a/init/Kconfig +++ b/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