initial commit

1 files changed, 35 insertions, 0 deletions

diff --git a/kern/usermem_asm.S b/kern/usermem_asm.S
new file mode 100644
index 0000000..0eee6f8
--- /dev/null
+++ b/kern/usermem_asm.S
@@ -0,0 +1,35 @@
+/** @file usermem_asm.S
+ *
+ *  @brief userspace r/w functions.
+ *
+ *  @author Hanjie Wu (hanjiew)
+ *  @bug No functional bugs
+ */
+
+.text
+
+.global try_read
+.type try_read, %function
+try_read:
+    mov 0x4(%esp), %eax
+    mov 0x8(%esp), %esi
+    mov (%eax), %al
+    mov %al, (%esi)
+    xor %eax, %eax
+    ret
+
+.global try_write
+.type try_write, %function
+try_write:
+    mov 0x4(%esp), %eax
+    mov 0x8(%esp), %edx
+    mov %dl, (%eax)
+    xor %eax, %eax
+    ret
+
+/* unsuccessful r/w will jump to this function and we return 1 */
+.global usermem_fail
+.type usermem_fail, %function
+usermem_fail:
+    mov $0xffffffff, %eax
+    ret