From 7d7620405324693b7f6e9690e75ccede66b8f757 Mon Sep 17 00:00:00 2001
From: Danila Fedorin <danila.fedorin@gmail.com>
Date: Wed, 24 Apr 2019 23:49:13 -0700
Subject: [PATCH] Add debugging kernel monitor functions

---
 kern/monitor.c | 42 +++++++++++++++++++++++++++++++++++++++++-
 kern/monitor.h |  2 ++
 kern/trap.c    |  2 +-
 3 files changed, 44 insertions(+), 2 deletions(-)

diff --git a/kern/monitor.c b/kern/monitor.c
index d2affd9..89e6efd 100644
--- a/kern/monitor.c
+++ b/kern/monitor.c
@@ -7,6 +7,7 @@
 #include <inc/assert.h>
 #include <inc/x86.h>
 
+#include <kern/env.h>
 #include <kern/ansi.h>
 #include <kern/console.h>
 #include <kern/monitor.h>
@@ -31,7 +32,9 @@ static struct Command commands[] = {
 	{ "kerninfo", "Display information about the kernel", mon_kerninfo },
 	{ "backtrace", "Display current backtrace", mon_backtrace },
 	{ "showmappings", "Display the physical mappings for range", mon_showmappings },
-	{ "mperms", "Change the permissions of a memory range", mon_mperms }
+	{ "mperms", "Change the permissions of a memory range", mon_mperms },
+	{ "resume", "Resume from a breakpoint", mon_resume },
+	{ "step", "Step to next instruction", mon_step }
 	
 };
 
@@ -188,6 +191,43 @@ int mon_mperms(int argc, char** argv, struct Trapframe* tf) {
 	return 0;
 }
 
+// This is a nice thought and all...
+// But we should modify the trap frame.
+// I feel stupid.
+static inline void
+set_eflag(uint16_t flagno, int value) {
+	uint32_t temp;
+	uint32_t mask = ~(1 << flagno);
+	uint32_t regv = value << flagno;
+	asm volatile("pushfl\n\t"
+			"pop %w0\n\t"
+			"and %w1, %w0\n\t"
+			"or %w2, %w0\n\t"
+			"push %w0\n\t"
+			"popfl\n\t"
+			: "=r" (temp)
+			: "r" (mask), "r" (regv));
+}
+
+#define EXPECT_BRKPT if(!(tf->tf_trapno == T_BRKPT || tf->tf_trapno == T_DEBUG)) { \
+	cprintf(ACOL_ERR("I don't think I should resume from this.\n")); \
+	return 0; }
+#define EFLAGS_TF 0x8
+
+int mon_resume(int argc, char** argv, struct Trapframe* tf) {
+	EXPECT_BRKPT;
+	tf->tf_eflags &= ~(1 << EFLAGS_TF);
+	env_pop_tf(tf);
+	return 0;
+}
+
+int mon_step(int argc, char** argv, struct Trapframe* tf) {
+	EXPECT_BRKPT;
+	tf->tf_eflags |= 1 << EFLAGS_TF;
+	env_pop_tf(tf);
+	return 0;
+}
+
 /***** Kernel monitor command interpreter *****/
 
 #define WHITESPACE "\t\r\n "
diff --git a/kern/monitor.h b/kern/monitor.h
index 4da7606..0e51db1 100644
--- a/kern/monitor.h
+++ b/kern/monitor.h
@@ -17,5 +17,7 @@ int mon_kerninfo(int argc, char **argv, struct Trapframe *tf);
 int mon_backtrace(int argc, char **argv, struct Trapframe *tf);
 int mon_showmappings(int argc, char **argv, struct Trapframe *tf);
 int mon_mperms(int argc, char** argv, struct Trapframe* tf);
+int mon_resume(int argc, char** argv, struct Trapframe* tf);
+int mon_step(int argc, char** argv, struct Trapframe* tf);
 
 #endif	// !JOS_KERN_MONITOR_H
diff --git a/kern/trap.c b/kern/trap.c
index 88ca879..4ce2170 100644
--- a/kern/trap.c
+++ b/kern/trap.c
@@ -199,7 +199,7 @@ trap_dispatch(struct Trapframe *tf)
 	if (tf->tf_trapno == T_PGFLT) {
 		page_fault_handler(tf);
 		return;
-	} else if (tf->tf_trapno == T_BRKPT) {
+	} else if (tf->tf_trapno == T_BRKPT || tf->tf_trapno == T_DEBUG) {
 		monitor(tf);
 		return;
 	} else if (tf->tf_trapno == T_SYSCALL) {