[Qemu-devel] [PATCH] mmap-alloc: check before use for ptr pointer

[Gonglei]

If ptr mmap failed, we don't need to do a superfluous
calculation for offset variable by ptr (MAP_FAILED).

Signed-off-by: Gonglei <address@hidden>
---
 util/mmap-alloc.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
index 5a85aa3..577862b 100644
--- a/util/mmap-alloc.c
+++ b/util/mmap-alloc.c
@@ -61,13 +61,15 @@ void *qemu_ram_mmap(int fd, size_t size, size_t align, bool 
shared)
 #else
     void *ptr = mmap(0, total, PROT_NONE, MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);
 #endif
-    size_t offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;
+    size_t offset;
     void *ptr1;
 
     if (ptr == MAP_FAILED) {
         return MAP_FAILED;
     }
 
+    offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;
+
     /* Make sure align is a power of 2 */
     assert(!(align & (align - 1)));
     /* Always align to host page size */
-- 
1.8.3.1