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[Qemu-block] [PATCH] osdep: Fix ROUND_UP(64-bit, 32-bit)
From: |
Eric Blake |
Subject: |
[Qemu-block] [PATCH] osdep: Fix ROUND_UP(64-bit, 32-bit) |
Date: |
Wed, 13 Sep 2017 16:03:43 -0500 |
When using bit-wise operations that exploit the power-of-two
nature of the second argument of ROUND_UP(), we still need to
ensure that the mask is as wide as the first argument (done
by using addition of 0 to force proper arithmetic promotion).
Unpatched, ROUND_UP(2ULL*1024*1024*1024*1024, 512) produces 0,
instead of the intended 2TiB.
Broken since its introduction in commit 292c8e50 (v1.5.0).
CC: address@hidden
Signed-off-by: Eric Blake <address@hidden>
---
I did not audit to see how many potential users of ROUND_UP
are actually passing in different sized types where the first
argument can be larger than UINT32_MAX; I stumbled across the
problem when iotests 190 started failing on a patch where I
added a new use. We can either be conservative and put this
on qemu-stable no matter what, or go through the effort of an
audit to see what might be broken (many callers in the block
layer, but not just there).
---
include/qemu/osdep.h | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/include/qemu/osdep.h b/include/qemu/osdep.h
index 6855b94bbf..7a3000efc5 100644
--- a/include/qemu/osdep.h
+++ b/include/qemu/osdep.h
@@ -189,13 +189,13 @@ extern int daemon(int, int);
/* Round number up to multiple. Requires that d be a power of 2 (see
* QEMU_ALIGN_UP for a safer but slower version on arbitrary
- * numbers) */
+ * numbers); works even if d is a smaller type than n. */
#ifndef ROUND_UP
-#define ROUND_UP(n,d) (((n) + (d) - 1) & -(d))
+#define ROUND_UP(n, d) (((n) + (d) - 1) & -((n) - (n) + (d)))
#endif
#ifndef DIV_ROUND_UP
-#define DIV_ROUND_UP(n,d) (((n) + (d) - 1) / (d))
+#define DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))
#endif
/*
--
2.13.5
- [Qemu-block] [PATCH] osdep: Fix ROUND_UP(64-bit, 32-bit),
Eric Blake <=