[Qemu-block] [PATCH for-2.8 v2] hbitmap: Fix shifts of constants by granularity

[Max Reitz]

An hbitmap's granularity may be anything from 0 to 63, so when shifting
constants by its value, they should not be plain ints.

Even having changed the types, hbitmap_serialization_granularity() still
tries to shift 64 to the right by the granularity. This operation is
undefined if the granularity is greater than 57. Adding an assertion is
fine for now, because serializing is done only in tests so far, but this
means that only bitmaps with a granularity below 58 can be serialized
and we should thus add a hbitmap_is_serializable() function later.

One of the two places touched in this patch uses
QEMU_ALIGN_UP(x, 1 << y). We can use ROUND_UP() there, since the second
parameter is obviously a power of two.

Signed-off-by: Max Reitz <address@hidden>
---
v2:
- Fix the same issue in hbitmap_truncate() [Stefan]
- Use ROUND_UP() instead of QEMU_ALIGN_UP() there (because we can)
- Add an assertion to hbitmap_serialization_granularity() guaranteeing
  that the shift doesn't overflow; we can guarantee this so far because
  the only place where serialization functions are used in is the
  hbitmap test
  (I'll send a follow-up patch to allow users to check whether a certain
  bitmap can be (de-)serialized)
---
 util/hbitmap.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/util/hbitmap.c b/util/hbitmap.c
index 5d1a21c..9f691b7 100644
--- a/util/hbitmap.c
+++ b/util/hbitmap.c
@@ -399,9 +399,13 @@ bool hbitmap_get(const HBitmap *hb, uint64_t item)
 
 uint64_t hbitmap_serialization_granularity(const HBitmap *hb)
 {
+    /* Must hold true so that the shift below is defined
+     * (ld(64) == 6, i.e. 1 << 6 == 64) */
+    assert(hb->granularity < 64 - 6);
+
     /* Require at least 64 bit granularity to be safe on both 64 bit and 32 bit
      * hosts. */
-    return 64 << hb->granularity;
+    return UINT64_C(64) << hb->granularity;
 }
 
 /* Start should be aligned to serialization granularity, chunk size should be
@@ -594,7 +598,7 @@ void hbitmap_truncate(HBitmap *hb, uint64_t size)
     if (shrink) {
         /* Don't clear partial granularity groups;
          * start at the first full one. */
-        uint64_t start = QEMU_ALIGN_UP(num_elements, 1 << hb->granularity);
+        uint64_t start = ROUND_UP(num_elements, UINT64_C(1) << 
hb->granularity);
         uint64_t fix_count = (hb->size << hb->granularity) - start;
 
         assert(fix_count);
-- 
2.10.2