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Keep right operand within width when right shifting

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NUM_IN_PAGE could return a value much larger than 64. According to the
C11 spec 6.5.7 paragraph 3 this is undefined behavior:

> If the value of the right operand is negative or is greater than or
> equal to the width of the promoted left operand, the behavior is
> undefined.

On most platforms, this is usually not a problem as the architecture
will mask off all out-of-range bits.
This commit is contained in:
Peter Zhu 2022-01-24 13:38:15 -05:00
parent 97ab2599f3
commit 87784fdeb2
Notes: git 2022-01-25 04:34:36 +09:00
1 changed files with 1 additions and 1 deletions
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2
gc.c
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@ -4956,7 +4956,7 @@ try_move(rb_objspace_t *objspace, rb_heap_t *heap, struct heap_page *sweep_page,
bits_t bits = mark_bits[index] & ~pin_bits[index];
bits >>= NUM_IN_PAGE(p);
bits >>= NUM_IN_PAGE(p) % BITS_BITLENGTH;
if (try_move_plane(objspace, heap, sweep_page, (uintptr_t)p, bits, dest)) return 1;
if (index == 0) {