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diff --git a/doc/userprog.texi b/doc/userprog.texi
index 525e8ce..0746b2e 100644
--- a/doc/userprog.texi
+++ b/doc/userprog.texi
@@ -247,12 +247,32 @@ requirements:
 
 @itemize @bullet
 @item
-The kernel should print out the program's name and exit status
-whenever a process terminates, e.g.@: @code{shell: exit(-1)}, whether
-termination is due to a call to the @code{exit} system call or for
-another reason.  The name printed should be the full name passed to
+The kernel should print out the program's name and exit status whenever
+a process terminates, whether termination is caused by the @code{exit}
+system call or for another reason.
+
+@itemize @minus
+@item
+The message must be formatted exactly as if it was printed with
+@code{printf ("%s: exit(%d)\n", @dots{});} given appropriate arguments.
+
+@item
+The name printed should be the full name passed to
 @func{process_execute}, except that it is acceptable to truncate it to
-15 characters to allow for the limited space in @struct{thread}.
+15 characters to allow for the limited space in @struct{thread}.  The
+name printed need not include arguments.
+
+@item
+Do not print a message when a kernel thread that is not a process
+terminates.
+
+@item
+Do not print messages about process termination for the @code{halt}
+system call.
+
+@item
+No message need be printed when a process fails to load.
+@end itemize
 
 @item
 Aside from this, the kernel should print out no other messages that
@@ -345,7 +365,7 @@ conditions (usually errors).
 @itemx pid_t exec (const char *@var{cmd_line})
 Runs the executable whose name is given in @var{cmd_line}, passing any
 given arguments, and returns the new process's program id (pid).  If
-there is an error loading this program, returns pid -1, which
+there is an error loading this program, may return pid -1, which
 otherwise should not be a valid id number.
 
 @item SYS_join
@@ -446,7 +466,7 @@ the @file{filesys} directory, and release it afterward.  Don't forget
 that @func{process_execute} also accesses files.  @strong{For now, we
 recommend against modifying code in the @file{filesys} directory.}
 
-We have provided you a function for each system call in
+We have provided you a user-level function for each system call in
 @file{lib/user/syscall.c}.  These provide a way for user processes to
 invoke each system call from a C program.  Each of them calls an
 assembly language routine in @file{lib/user/syscall-stub.S}, which in
@@ -507,7 +527,8 @@ 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
@@ -818,7 +839,7 @@ After we push all of the strings onto the stack, we adjust the stack
 pointer so that it is word-aligned: that is, we move it down to the
 next 4-byte boundary.  This is required because we will next be
 placing several words of data on the stack, and they must be aligned
-in order to be read correctly.  In our example, as you'll see below,
+to be read correctly.  In our example, as you'll see below,
 the strings start at address @t{0xffed}.  One word below that would be
 at @t{0xffe9}, so we could in theory put the next word on the stack
 there.  However, since the stack pointer should always be
@@ -950,3 +971,9 @@ In this example, the caller's stack pointer would be at
 The 80@var{x}86 convention for function return values is to place them
 in the @samp{EAX} register.  System calls that return a value can do
 so by modifying the @samp{eax} member of @struct{intr_frame}.
+
+You should try to avoid writing large amounts of repetitive code for
+implementing system calls.  Each system call argument, whether an
+integer or a pointer, takes up 4 bytes on the stack.  You should be able
+to take advantage of this to avoid writing much near-identical code for
+retrieving each system call's arguments from the stack.