add fortified implementations of pread/pread64

Change-Id: Iec39c3917e0bc94371bd81541619392f5abe29b9
diff --git a/libc/include/unistd.h b/libc/include/unistd.h
index 92d3abe..a601cb7 100644
--- a/libc/include/unistd.h
+++ b/libc/include/unistd.h
@@ -224,6 +224,16 @@
     } while (_rc == -1 && errno == EINTR); \
     _rc; })
 
+extern ssize_t __pread_chk(int, void*, size_t, off_t, size_t);
+__errordecl(__pread_dest_size_error, "pread called with size bigger than destination");
+__errordecl(__pread_count_toobig_error, "pread called with count > SSIZE_MAX");
+extern ssize_t __pread_real(int, void*, size_t, off_t) __RENAME(pread);
+
+extern ssize_t __pread64_chk(int, void*, size_t, off64_t, size_t);
+__errordecl(__pread64_dest_size_error, "pread64 called with size bigger than destination");
+__errordecl(__pread64_count_toobig_error, "pread64 called with count > SSIZE_MAX");
+extern ssize_t __pread64_real(int, void*, size_t, off64_t) __RENAME(pread64);
+
 extern ssize_t __read_chk(int, void*, size_t, size_t);
 __errordecl(__read_dest_size_error, "read called with size bigger than destination");
 __errordecl(__read_count_toobig_error, "read called with count > SSIZE_MAX");
@@ -231,6 +241,62 @@
 
 #if defined(__BIONIC_FORTIFY)
 
+#if defined(__USE_FILE_OFFSET64)
+#define __PREAD_PREFIX(x) __pread64_ ## x
+#else
+#define __PREAD_PREFIX(x) __pread_ ## x
+#endif
+
+__BIONIC_FORTIFY_INLINE
+ssize_t pread(int fd, void* buf, size_t count, off_t offset) {
+    size_t bos = __bos0(buf);
+
+#if !defined(__clang__)
+    if (__builtin_constant_p(count) && (count > SSIZE_MAX)) {
+        __PREAD_PREFIX(count_toobig_error)();
+    }
+
+    if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
+        return __PREAD_PREFIX(real)(fd, buf, count, offset);
+    }
+
+    if (__builtin_constant_p(count) && (count > bos)) {
+        __PREAD_PREFIX(dest_size_error)();
+    }
+
+    if (__builtin_constant_p(count) && (count <= bos)) {
+        return __PREAD_PREFIX(real)(fd, buf, count, offset);
+    }
+#endif
+
+    return __PREAD_PREFIX(chk)(fd, buf, count, offset, bos);
+}
+
+__BIONIC_FORTIFY_INLINE
+ssize_t pread64(int fd, void* buf, size_t count, off64_t offset) {
+    size_t bos = __bos0(buf);
+
+#if !defined(__clang__)
+    if (__builtin_constant_p(count) && (count > SSIZE_MAX)) {
+        __pread64_count_toobig_error();
+    }
+
+    if (bos == __BIONIC_FORTIFY_UNKNOWN_SIZE) {
+        return __pread64_real(fd, buf, count, offset);
+    }
+
+    if (__builtin_constant_p(count) && (count > bos)) {
+        __pread64_dest_size_error();
+    }
+
+    if (__builtin_constant_p(count) && (count <= bos)) {
+        return __pread64_real(fd, buf, count, offset);
+    }
+#endif
+
+    return __pread64_chk(fd, buf, count, offset, bos);
+}
+
 __BIONIC_FORTIFY_INLINE
 ssize_t read(int fd, void* buf, size_t count) {
     size_t bos = __bos0(buf);
@@ -255,6 +321,7 @@
 
     return __read_chk(fd, buf, count, bos);
 }
+
 #endif /* defined(__BIONIC_FORTIFY) */
 
 __END_DECLS