From be742759b0b350dcd159c77f68790b9c6372b0c0 Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Sun, 4 Mar 2018 01:53:59 -0500 Subject: [PATCH] osdep: Fix ROUND_UP(64-bit, 32-bit) 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 a ternary to force proper arithmetic promotion). Unpatched, ROUND_UP(2ULL*1024*1024*1024*1024, 512U) produces 0, instead of the intended 2TiB, because negation of an unsigned 32-bit quantity followed by widening to 64-bits does not sign-extend the mask. Broken since its introduction in commit 292c8e50 (v1.5.0). Callers that passed the same width type to both macro parameters, or that had other code to ensure the first parameter's maximum runtime value did not exceed the second parameter's width, are unaffected, but I did not audit to see which (if any) existing clients of the macro could trigger incorrect behavior (I found the bug while adding a new use of the macro). While preparing the patch, checkpatch complained about poor spacing, so I also fixed that here and in the nearby DIV_ROUND_UP. Backports commit 33a599667a9e70588483a31286dfff8cfc27d513 from qemu --- qemu/include/qemu/osdep.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/qemu/include/qemu/osdep.h b/qemu/include/qemu/osdep.h index 35174a04..0d78a456 100644 --- a/qemu/include/qemu/osdep.h +++ b/qemu/include/qemu/osdep.h @@ -175,13 +175,13 @@ /* 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) & -(0 ? (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 #ifdef _MSC_VER