From: Ben Pfaff <blp@cs.stanford.edu>
Date: Wed, 15 Dec 2004 05:50:42 +0000 (+0000)
Subject: Use 0xcc (not 0xcd) for clearing malloc() blocks too.
X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=1d50ca8650fb96c13add16ef5659cc7aa6d4ab4b;p=pintos-anon

Use 0xcc (not 0xcd) for clearing malloc() blocks too.
Update documentation.
---

diff --git a/doc/debug.texi b/doc/debug.texi
index a192a73..f93eeda 100644
--- a/doc/debug.texi
+++ b/doc/debug.texi
@@ -374,17 +374,18 @@ above, a good place to start adding @func{printf}s is
 @node Debugging Tips
 @section Tips
 
-The page allocator in @file{threads/palloc.c} clears all the bytes in
-pages to @t{0xcc} when they are freed.  Thus, if you see an attempt to
+The page allocator in @file{threads/palloc.c} and the block allocator in
+@file{threads/malloc.c} both clear all the bytes in pages and blocks to
+@t{0xcc} when they are freed.  Thus, if you see an attempt to
 dereference a pointer like @t{0xcccccccc}, or some other reference to
 @t{0xcc}, there's a good chance you're trying to reuse a page that's
-already been freed.  Also, byte @t{0xcc} is the CPU opcode for
-``invoke interrupt 3,'' so if you see an error like @code{Interrupt
-0x03 (#BP Breakpoint Exception)}, Pintos tried to execute code in a
-freed page.
-
-Similarly, the block allocator in @file{threads/malloc.c} clears all
-the bytes in freed blocks to @t{0xcd}.  The two bytes @t{0xcdcd} are
-a CPU opcode for ``invoke interrupt @t{0xcd},'' so @code{Interrupt
-0xcd (unknown)} is a good sign that you tried to execute code in a
-block freed with @func{free}.
+already been freed.  Also, byte @t{0xcc} is the CPU opcode for ``invoke
+interrupt 3,'' so if you see an error like @code{Interrupt 0x03 (#BP
+Breakpoint Exception)}, Pintos tried to execute code in a freed page or
+block.
+
+An assertion failure on the expression @code{sec_no < d->capacity}
+indicates that Pintos tried to access a file through an inode that has
+been closed and freed.  Freeing an inode clears its starting sector
+number to @t{0xcccccccc}, which is not a valid sector number for disks
+smaller than about 1.6 TB.
diff --git a/src/threads/malloc.c b/src/threads/malloc.c
index 2077354..0cb5f9d 100644
--- a/src/threads/malloc.c
+++ b/src/threads/malloc.c
@@ -198,7 +198,7 @@ free (void *p)
     }
 
 #ifndef NDEBUG
-  memset (b, 0xcd, d->block_size);
+  memset (b, 0xcc, d->block_size);
 #endif
   
   lock_acquire (&d->lock);