From 968211392d613c12e68baa69321e8be32f487005 Mon Sep 17 00:00:00 2001
From: Carlos Fenollosa <carlos.fenollosa@gmail.com>
Date: Mon, 20 Oct 2014 23:21:20 +0200
Subject: [PATCH] lesson 14

---
 14-checkpoint/Makefile          |  10 +++++-----
 14-checkpoint/README.md         |  11 ++++++++---
 14-checkpoint/boot/bootsect.bin | Bin 0 -> 512 bytes
 14-checkpoint/kernel/kernel.o   | Bin 0 -> 1936 bytes
 4 files changed, 13 insertions(+), 8 deletions(-)
 create mode 100644 14-checkpoint/boot/bootsect.bin
 create mode 100644 14-checkpoint/kernel/kernel.o

diff --git a/14-checkpoint/Makefile b/14-checkpoint/Makefile
index 61497ea..2756535 100644
--- a/14-checkpoint/Makefile
+++ b/14-checkpoint/Makefile
@@ -12,9 +12,13 @@ CFLAGS = -g
 os-image.bin: boot/bootsect.bin kernel.bin
 	cat $^ > os-image.bin
 
-kernel.bin: kernel.elf
+kernel.bin: boot/kernel_entry.o ${OBJ}
 	i386-elf-ld -o $@ -Ttext 0x1000 $^ --oformat binary
 
+# Used for debugging purposes
+kernel.elf: boot/kernel_entry.o ${OBJ}
+	i386-elf-ld -o $@ -Ttext 0x1000 $^ 
+
 run: os-image.bin
 	qemu-system-i386 -fda os-image.bin
 
@@ -22,10 +26,6 @@ debug: os-image.bin kernel.elf
 	qemu-system-i386 -s -fda os-image.bin &
 	${GDB} -ex "target remote localhost:1234" -ex "symbol-file kernel.elf"
 
-# To build the kernel: make all objects first
-kernel.elf: boot/kernel_entry.o ${OBJ}
-	i386-elf-ld -o $@ -Ttext 0x1000 $^ 
-
 # To make an object, always compile from its .c
 %.o: %.c ${HEADERS}
 	${CC} ${CFLAGS} -ffreestanding -c $< -o $@
diff --git a/14-checkpoint/README.md b/14-checkpoint/README.md
index cf31211..56c608f 100644
--- a/14-checkpoint/README.md
+++ b/14-checkpoint/README.md
@@ -31,8 +31,12 @@ make
 make install
 ```
 
-Check out the Makefile target `make debug`. We can take
-advantage of this cool qemu feature. Type `make debug` and, on the gdb shell:
+Check out the Makefile target `make debug`. This target uses builds `kernel.elf`, which
+is an object file (not binary) with all the symbols we generated on the kernel, thanks to
+the `-g` flag on gcc. Please examine it with `xxd` and you'll see some strings. Actually,
+the correct way to examine the strings in an object file is by `strings kernel.elf`
+
+We can take advantage of this cool qemu feature. Type `make debug` and, on the gdb shell:
 
 - Set up a breakpoint in `kernel.c:main()`: `b main`
 - Run the OS: `continue`
@@ -44,7 +48,8 @@ advantage of this cool qemu feature. Type `make debug` and, on the gdb shell:
 - `next` to put there our 'X'
 - Let's make sure: `print *video_memory` and look at the qemu screen. It's definitely there.
 
-Now is a good time to read some tutorial on `gdb`!
+Now is a good time to read some tutorial on `gdb` and learn super useful things like `info registers`
+which will save us a lot of time in the future!
 
 
 Strategy
diff --git a/14-checkpoint/boot/bootsect.bin b/14-checkpoint/boot/bootsect.bin
new file mode 100644
index 0000000000000000000000000000000000000000..e8d27fbfebf937aaa6263436ba130a44bd615eda
GIT binary patch
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diff --git a/14-checkpoint/kernel/kernel.o b/14-checkpoint/kernel/kernel.o
new file mode 100644
index 0000000000000000000000000000000000000000..c7cfa2e54c46d6deae1031809589bb0c71a2cbf0
GIT binary patch
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literal 0
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