From 5d8bffd11b0e8fb997778d986a3de46e03ab6146 Mon Sep 17 00:00:00 2001
From: John Franklin <jfranklin9000@gmail.com>
Date: Mon, 19 Oct 2015 10:10:23 -0500
Subject: [PATCH 1/2] print loom and fix a range calculation in u3e_fault()

---
 noun/events.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/noun/events.c b/noun/events.c
index 7b6c89d92..a32fc0b9f 100644
--- a/noun/events.c
+++ b/noun/events.c
@@ -115,8 +115,9 @@ u3e_fault(void* adr_v, c3_i ser_i)
 {
   c3_w* adr_w = (c3_w*) adr_v;
 
-  if ( (adr_w < u3_Loom) || (adr_w > (u3_Loom + u3a_words)) ) {
+  if ( (adr_w < u3_Loom) || (adr_w >= (u3_Loom + u3a_words)) ) {
     fprintf(stderr, "address %p out of loom!\r\n", adr_v);
+    fprintf(stderr, "loom: [%p : %p)\r\n", u3_Loom, u3_Loom + u3a_words);
     c3_assert(0);
     return 0;
   }

From fcc8e8ada239a2d468b5b8f767fd1caf1d4da5c3 Mon Sep 17 00:00:00 2001
From: John Franklin <jfranklin9000@gmail.com>
Date: Mon, 19 Oct 2015 03:33:25 -0500
Subject: [PATCH 2/2] Add notes on debugging with gdb.

---
 CONTRIBUTING.md | 24 ++++++++++++++++++++++++
 Makefile        | 10 +++++++++-
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index bb9d596b3..a67b830ac 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -145,6 +145,30 @@ Just do the same procedure to create a new, merged pill before
 committing the merge. Otherwise, just make sure to use the correct
 `urbit.pill` for each commit.
 
+## Debug urbit with `gdb`
+
+Follow the build instructions in README.md but run `make` with argument `DEBUG=yes`:
+
+(If you've already built urbit first run `make clean`.)
+
+    make DEBUG=yes
+
+Run `gdb`, while loading `bin/urbit` and its symbol table:
+
+    gdb bin/urbit
+
+Set a breakpoint on `main()` (optional):
+
+    break main
+
+Run your urbit comet `mycomet`:
+
+    run mycomet
+
+Continue from the breakpoint on `main()`:
+
+    continue
+
 ## What to work on
 
 If you are not thinking of contributing with a specific goal in mind,
diff --git a/Makefile b/Makefile
index 7160cb2c2..a4ed3c502 100644
--- a/Makefile
+++ b/Makefile
@@ -70,10 +70,18 @@ endif
 INCLUDE=include
 MDEFINES=-DU3_OS_$(OS) -DU3_OS_ENDIAN_$(ENDIAN) -D U3_LIB=\"$(LIB)\"
 
+DEBUG=no
+
+ifeq ($(DEBUG),yes)
+DEBUGFLAGS=-g
+else
+DEBUGFLAGS=-O3
+endif
+
 # NOTFORCHECKIN - restore -O3
 # 	-DGHETTO \
 #   -DHUSH
-CFLAGS= $(COSFLAGS) -O3 -ffast-math \
+CFLAGS= $(COSFLAGS) $(DEBUGFLAGS) -ffast-math \
 	-funsigned-char \
 	-I/usr/local/include \
 	-I/opt/local/include \