[Qemu-devel] [PATCH v2] util/mmap-alloc: check parameter before using

[Cao jin]

Also refactor a little for readability

Signed-off-by: Cao jin <address@hidden>
---
 util/mmap-alloc.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/util/mmap-alloc.c b/util/mmap-alloc.c
index 5a85aa3..a32ee53 100644
--- a/util/mmap-alloc.c
+++ b/util/mmap-alloc.c
@@ -61,7 +61,7 @@ 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) {
@@ -73,6 +73,7 @@ void *qemu_ram_mmap(int fd, size_t size, size_t align, bool 
shared)
     /* Always align to host page size */
     assert(align >= getpagesize());
 
+    offset = QEMU_ALIGN_UP((uintptr_t)ptr, align) - (uintptr_t)ptr;
     ptr1 = mmap(ptr + offset, size, PROT_READ | PROT_WRITE,
                 MAP_FIXED |
                 (fd == -1 ? MAP_ANONYMOUS : 0) |
@@ -83,22 +84,20 @@ void *qemu_ram_mmap(int fd, size_t size, size_t align, bool 
shared)
         return MAP_FAILED;
     }
 
-    ptr += offset;
-    total -= offset;
-
     if (offset > 0) {
-        munmap(ptr - offset, offset);
+        munmap(ptr, offset);
     }
 
     /*
      * Leave a single PROT_NONE page allocated after the RAM block, to serve as
      * a guard page guarding against potential buffer overflows.
      */
+    total -= offset;
     if (total > size + getpagesize()) {
-        munmap(ptr + size + getpagesize(), total - size - getpagesize());
+        munmap(ptr1 + size + getpagesize(), total - size - getpagesize());
     }
 
-    return ptr;
+    return ptr1;
 }
 
 void qemu_ram_munmap(void *ptr, size_t size)
-- 
2.1.0