X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=doc%2Fuserprog.texi;h=9db073776ab70c7fadb9e711325b991a23e5e552;hb=c3db4f872fdc6ac50cd5bfde5117467b40bd54db;hp=72e8d8177a07b4641b3762e275b6e71e740b0a40;hpb=3ed7340d796b1a5cafe45ec78b80415f09eb3fa9;p=pintos-anon

diff --git a/doc/userprog.texi b/doc/userprog.texi
index 72e8d81..9db0737 100644
--- a/doc/userprog.texi
+++ b/doc/userprog.texi
@@ -405,9 +405,9 @@ conditions (usually errors).
 @item SYS_exec
 @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, may return pid -1, which
-otherwise should not be a valid id number.
+given arguments, and returns the new process's program id (pid).  Must
+return pid -1, which otherwise should not be a valid program id, if
+there is an error loading this program.
 
 @item SYS_join
 @itemx int join (pid_t @var{pid})
@@ -456,7 +456,13 @@ than end of file).  Fd 0 reads from the keyboard using
 @itemx int write (int @var{fd}, const void *@var{buffer}, unsigned @var{size})
 Write @var{size} bytes from @var{buffer} to the open file @var{fd}.
 Returns the number of bytes actually written, or -1 if the file could
-not be written.   Fd 1 writes to the console.
+not be written.   
+
+Fd 1 writes to the console.  Your code to write to the console should
+write all of @var{buffer} in one call to @func{putbuf}, at least as
+long as @var{size} is not bigger than a few hundred bytes.  Otherwise,
+lines of text output by different processes may end up interleaved on
+the console, confusing both human readers and our grading scripts.
 
 @item SYS_seek
 @itemx void seek (int @var{fd}, unsigned @var{position})
@@ -510,9 +516,9 @@ recommend against modifying code in the @file{filesys} directory.}
 
 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
-turn invokes the system call interrupt and returns.
+invoke each system call from a C program.  Each uses a little inline
+assembly code to invoke the system call and (if appropriate) returns the
+system call's return value.
 
 When you're done with this part, and forevermore, Pintos should be
 bulletproof.  Nothing that a user program can do should ever cause the
@@ -680,7 +686,7 @@ provide a little bit of helpful code:
    Returns true if successful, false if USRC is invalid. */
 static inline bool get_user (uint8_t *dst, const uint8_t *usrc) {
   int eax;
-  asm ("movl $1f, %%eax; movb %2, %%al; movb %%al, %0; 1:"
+  asm ("mov %%eax, offset 1f; mov %%al, %2; mov %0, %%al; 1:"
        : "=m" (*dst), "=&a" (eax) : "m" (*usrc));
   return eax != 0;
 }
@@ -689,7 +695,7 @@ static inline bool get_user (uint8_t *dst, const uint8_t *usrc) {
    Returns true if successful, false if UDST is invalid. */
 static inline bool put_user (uint8_t *udst, uint8_t byte) {
   int eax;
-  asm ("movl $1f, %%eax; movb %b2, %0; 1:"
+  asm ("mov %%eax, offset 1f; mov %0, %b2; 1:"
        : "=m" (*udst), "=&a" (eax) : "r" (byte));
   return eax != 0;
 }