Clarifications.

diff --git a/doc/userprog.texi b/doc/userprog.texi
index 32934965f4c44cc805de4b930ea4f56be4436ce2..f70957f6617ba4a39f32b6a9f7129adb0214d620 100644 (file)
--- a/doc/userprog.texi
+++ b/doc/userprog.texi
@@ -520,7 +520,8 @@ isn't properly set up yet, this causes a page fault.
 @samp{system call!}.}
 
 Every reasonable program tries to make at least one system call
-(@func{exit}) and most programs make more than that.  The default
+(@func{exit}) and most programs make more than that.  Notably,
+@func{printf} invokes the @code{write} system call.  The default
 system call handler just prints @samp{system call!} and terminates the
 program.  You'll have to implement 2-2 before you see anything more
 interesting.  Until then, you can use @func{hex_dump} to convince