Avoid sign extension of the mmap offset.
off_t is signed to support seeking backwards, but that's a liability
when using off_t to represent a subset of a file.
Change-Id: I2a3615166eb16212347eb47f1242e3bfb93c2022
diff --git a/libc/bionic/mmap.cpp b/libc/bionic/mmap.cpp
index 864dea2..febc459 100644
--- a/libc/bionic/mmap.cpp
+++ b/libc/bionic/mmap.cpp
@@ -37,13 +37,14 @@
#define MMAP2_SHIFT 12 // 2**12 == 4096
-void* mmap(void* addr, size_t size, int prot, int flags, int fd, long offset) {
+void* mmap(void* addr, size_t size, int prot, int flags, int fd, off_t offset) {
if (offset & ((1UL << MMAP2_SHIFT)-1)) {
errno = EINVAL;
return MAP_FAILED;
}
- void* result = __mmap2(addr, size, prot, flags, fd, offset >> MMAP2_SHIFT);
+ size_t unsigned_offset = static_cast<size_t>(offset); // To avoid sign extension.
+ void* result = __mmap2(addr, size, prot, flags, fd, unsigned_offset >> MMAP2_SHIFT);
if (result != MAP_FAILED && (flags & (MAP_PRIVATE | MAP_ANONYMOUS)) != 0) {
ErrnoRestorer errno_restorer;
