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

[pintos-anon] / doc / debug.texi

diff --git a/doc/debug.texi b/doc/debug.texi
index 35e7c4af5e9e0fcb1caf8afa9f8867f898b5796e..f93eeda3ad0251375e96f8ac02b31ad06bd0aa60 100644 (file)
--- a/doc/debug.texi
+++ b/doc/debug.texi
@@ -217,13 +217,8 @@ The fifth and sixth lines are the interrupt handler entry path.
 The remaining lines are for addresses below @code{PHYS_BASE}.  This
 means that they refer to addresses in the user program, not in the
 kernel.  If you know what user program was running when the kernel
-panicked, you can re-run @command{backtrace} on the user program.  You
-need to have compiled the user program with debug symbols enabled for
-this to be useful.  Instructions for doing so are included in
-@file{pintos/src/Makefile.userprog}.
-
-In this case, we rerun @command{backtrace} like so (typing the command
-on a single line, of course):
+panicked, you can re-run @command{backtrace} on the user program, like
+so: (typing the command on a single line, of course):
 
 @example
 ~/cs140/pintos/src/utils/backtrace grow-too-big 0xc0106eff 0xc01102fb
@@ -305,14 +300,6 @@ address.
 (Use a @samp{0x} prefix to specify an address in hex.)
 @end table
 
-You might notice that @command{gdb} tends to show code being executed
-in an order different from the order in the source.  That is, the
-current statement jumps around seemingly randomly.  This is due to
-GCC's optimizer, which does tend to reorder code.  If it bothers you,
-you can turn off optimization by editing
-@file{pintos/src/Make.config}, removing @option{-O3} from the
-@code{CFLAGS} definition.
-
 If you notice other strange behavior while using @command{gdb}, there
 are three possibilities.  The first is that there is a bug in your
 modified Pintos.  The second is that there is a bug in Bochs's
@@ -387,17 +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.