os/os-android.h: fix alignment problems in shared memory functions

Fixes: #356 ("Android: SIGBUS due to unaligned access")

Signed-off-by: Omri Mor <omor1@asu.edu>

diff --git a/os/os-android.h b/os/os-android.h
index 6c3e0985b22fc5896e21d42458f02ff4b2be444c..f371116f8f6a9a45a37372b3044f71c77f88f368 100644 (file)
--- a/os/os-android.h
+++ b/os/os-android.h
@@ -98,7 +98,8 @@ static inline int shmget (key_t __key, size_t __size, int __shmflg)
        if (ret < 0)
                goto error;
 
-       ret = ioctl(fd, ASHMEM_SET_SIZE, __size);
+       /* Stores size in first 8 bytes, allocate extra space */
+       ret = ioctl(fd, ASHMEM_SET_SIZE, __size + sizeof(uint64_t));
        if (ret < 0)
                goto error;
 
@@ -111,19 +112,20 @@ error:
 
 static inline void *shmat (int __shmid, const void *__shmaddr, int __shmflg)
 {
-       size_t *ptr, size = ioctl(__shmid, ASHMEM_GET_SIZE, NULL);
-       ptr = mmap(NULL, size + sizeof(size_t), PROT_READ | PROT_WRITE, MAP_SHARED, __shmid, 0);
-       *ptr = size;    //save size at beginning of buffer, for use with munmap
-       return &ptr[1];
+       size_t size = ioctl(__shmid, ASHMEM_GET_SIZE, NULL);
+       /* Needs to be 8-byte aligned to prevent SIGBUS on 32-bit ARM */
+       uint64_t *ptr = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, __shmid, 0);
+       /* Save size at beginning of buffer, for use with munmap */
+       *ptr = size;
+       return ptr + 1;
 }
 
 static inline int shmdt (const void *__shmaddr)
 {
-       size_t *ptr, size;
-       ptr = (size_t *)__shmaddr;
-       ptr--;
-       size = *ptr;    //find mmap size which we stored at the beginning of the buffer
-       return munmap((void *)ptr, size + sizeof(size_t));
+       /* Find mmap size which we stored at the beginning of the buffer */
+       uint64_t *ptr = (uint64_t *)__shmaddr - 1;
+       size_t size = *ptr;
+       return munmap(ptr, size);
 }
 #endif