Messages in this thread | | | From | Alexander Potapenko <> | Date | Tue, 7 Nov 2023 17:33:56 +0100 | 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]' |
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On Tue, Nov 7, 2023 at 2:23 PM Alexander Lobakin <aleksander.lobakin@intel.com> wrote: > > From: Andy Shevchenko <andriy.shevchenko@linux.intel.com> > Date: Mon, 6 Nov 2023 20:23:52 +0200 > > > On Mon, Nov 06, 2023 at 05:31:34PM +0100, Alexander Lobakin wrote: > > > >>> | Reported-by: kernel test robot <lkp@intel.com> > >>> | Closes: https://lore.kernel.org/oe-kbuild-all/202310170708.fJzLlgDM-lkp@intel.com/ > > > >> Not sure how to approach this :z It was also captured on the version you > >> sent 2 weeks ago, so this could've been resolved already. > > > > Is it in the repository already? if so, we should revert it. > > Otherwise you have time to think and fix. > > Nah, neither Alex' series nor mine. And I'd say this should rather be > resolved in the functions Alex introduce. > > Thanks, > Olek
Sorry, I couldn't reproduce the problem using the instructions at https://download.01.org/0day-ci/archive/20231017/202310170708.fJzLlgDM-lkp@intel.com/reproduce locally, maybe that's because I only have gcc-11 and higher.
But if I'm understanding correctly what's going on, then GCC will be reporting the same issue in the following code:
======================================================= #include <stddef.h> #include <stdbool.h>
#define BITS_PER_LONG 64 #define unlikely(x) x #define UL(x) (x##UL) #define GENMASK(h, l) \ (((~UL(0)) - (UL(1) << (l)) + 1) & \ (~UL(0) >> (BITS_PER_LONG - 1 - (h))))
#define BIT_WORD(nr) ((nr) / BITS_PER_LONG) #define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & (BITS_PER_LONG - 1))) #define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1)))
inline void bitmap_write(unsigned long *map, unsigned long value, unsigned long start, unsigned long nbits) { size_t index; unsigned long offset; unsigned long space; unsigned long mask; bool fit;
if (unlikely(!nbits)) return;
mask = BITMAP_LAST_WORD_MASK(nbits); value &= mask; offset = start % BITS_PER_LONG; space = BITS_PER_LONG - offset; fit = space >= nbits; index = BIT_WORD(start);
map[index] &= (fit ? (~(mask << offset)) : ~BITMAP_FIRST_WORD_MASK(start)); map[index] |= value << offset; if (fit) return;
map[index + 1] &= BITMAP_FIRST_WORD_MASK(start + nbits); map[index + 1] |= (value >> space); }
unsigned long foo(unsigned int n) { unsigned long bm[1] = {0}; bitmap_write(bm, 1, n, 2); return bm[0]; } ======================================================= (see also https://godbolt.org/z/GfGfYje53)
If so, the problem is not specific to GCC 9, trunk GCC also barks on this code:
======================================================= In function 'bitmap_write', inlined from 'bitmap_write' at <source>:15:13, inlined from 'foo' at <source>:47:7: <source>:40:12: warning: array subscript 1 is outside array bounds of 'long unsigned int[1]' [-Warray-bounds=] 40 | map[index + 1] &= BITMAP_FIRST_WORD_MASK(start + nbits); | ~~~^~~~~~~~~~~ =======================================================
If this is true for the code in drivers/gpio/gpio-pca953x.c, suppressing the report for GCC 9 won't help for other versions. Given that this report is isolated in a single file, we probably need to give the compiler some hints about the range of values passed to bitmap_write() rather than suppressing the optimizations.
-- Alexander Potapenko Software Engineer
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