X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=doc%2Fuserprog.texi;h=8ed52b1e6aca46b28c40c9d4a962ee95ee28f7d5;hb=ad463f508ae96156401eaadf92e5801ba393e63d;hp=a9a84b2dcd854609cbd40bd82648cf96b1a9773c;hpb=f415a37905c57f61b444806bf84f5405184452aa;p=pintos-anon

diff --git a/doc/userprog.texi b/doc/userprog.texi
index a9a84b2..8ed52b1 100644
--- a/doc/userprog.texi
+++ b/doc/userprog.texi
@@ -20,10 +20,9 @@ assignment.  The ``alarm clock'' functionality may be useful in
 projects 3 and 4, but it is not strictly required.
 
 You might find it useful to go back and reread how to run the tests
-(@pxref{Testing}).  In particular, the tests for project 2 and later
-projects will probably run faster if you use the qemu emulator, e.g.@:
-via @code{make check PINTOSOPTS='--qemu'}.  The qemu emulator is
-available only on the Linux machines.
+(@pxref{Testing}).  In particular, the tests for project 2 (and later
+projects) will probably run faster if you use the qemu emulator, e.g.@:
+via @code{make check PINTOSOPTS='--qemu'}.
 
 @menu
 * Project 2 Background::        
@@ -430,29 +429,37 @@ Therefore, for those who want to try the latter technique, we'll
 provide a little bit of helpful code:
 
 @verbatim
-/* Tries to copy a byte from user address USRC to kernel address KDST.
-   Returns true if successful, false if USRC is invalid. */
-static inline bool get_user (uint8_t *kdst, const uint8_t *usrc) {
-  int eax;
-  asm ("movl $1f, %%eax; movb %2, %%al; movb %%al, %0; 1:"
-       : "=m" (*kdst), "=&a" (eax) : "m" (*usrc));
-  return eax != 0;
+/* Reads a byte at user virtual address UADDR.
+   UADDR must be below PHYS_BASE.
+   Returns the byte value if successful, -1 if a segfault
+   occurred. */
+static int
+get_user (const uint8_t *uaddr)
+{
+  int result;
+  asm ("movl $1f, %0; movzbl %1, %0; 1:"
+       : "=&a" (result) : "m" (*uaddr));
+  return result;
 }
-
-/* Tries to write BYTE to user address UDST.
-   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:"
-       : "=m" (*udst), "=&a" (eax) : "r" (byte));
-  return eax != 0;
+ 
+/* Writes BYTE to user address UDST.
+   UDST must be below PHYS_BASE.
+   Returns true if successful, false if a segfault occurred. */
+static bool
+put_user (uint8_t *udst, uint8_t byte)
+{
+  int error_code;
+  asm ("movl $1f, %0; movb %b2, %1; 1:"
+       : "=&a" (error_code), "=m" (*udst) : "r" (byte));
+  return error_code != -1;
 }
 @end verbatim
 
 Each of these functions assumes that the user address has already been
 verified to be below @code{PHYS_BASE}.  They also assume that you've
-modified @func{page_fault} so that a page fault in the kernel merely sets
-@code{eax} to 0 and copies its former value into @code{eip}.
+modified @func{page_fault} so that a page fault in the kernel merely
+sets @code{eax} to @t{0xffffffff} and copies its former value
+into @code{eip}.
 
 @node Project 2 Suggested Order of Implementation
 @section Suggested Order of Implementation