Add printVal() hypercall

defs.h

@@ -0,0 +1,2 @@
+#define PORT_PRINT_CHAR  0xE9
+#define PORT_PRINT_VALUE 0xEA

guest.c

@@ -1,8 +1,13 @@
 #include <stddef.h>
 #include <stdint.h>
+#include "defs.h"
 
-static void outb(uint16_t port, uint8_t value) {
-	asm("outb %0,%1" : /* empty */ : "a" (value), "Nd" (port) : "memory");
+static inline void outb(uint16_t port, uint32_t value) {
+  asm("out %0,%1" : /* empty */ : "a" (value), "Nd" (port) : "memory");
+}
+
+void printVal(uint32_t val) {
+	outb(PORT_PRINT_VALUE, val);
 }
 
 void
@@ -11,11 +16,16 @@ __attribute__((section(".start")))
 _start(void) {
 	const char *p;
 
+	/* Print Hello world */
 	for (p = "Hello, world!\n"; *p; ++p)
-		outb(0xE9, *p);
+		outb(PORT_PRINT_CHAR, *p);
 
-	*(long *) 0x400 = 42;
+	/* Test printVal() */
+	printVal(0x1234);
+	outb(PORT_PRINT_CHAR, '\n');
 
+	/* Halt after setting 0x400 & rax as 42 */
+	*(long *) 0x400 = 42;
 	for (;;)
 		asm("hlt" : /* empty */ : "a" (42) : "memory");
 }

kvm-hello-world.c

@@ -8,6 +8,7 @@
 #include <string.h>
 #include <stdint.h>
 #include <linux/kvm.h>
+#include "defs.h"
 
 /* CR0 bits */
 #define CR0_PE 1u
@@ -164,17 +165,26 @@ int run_vm(struct vm *vm, struct vcpu *vcpu, size_t sz)
 			exit(1);
 		}
 
+		// Guest exited.
+
 		switch (vcpu->kvm_run->exit_reason) {
 		case KVM_EXIT_HLT:
 			goto check;
 
 		case KVM_EXIT_IO:
-			if (vcpu->kvm_run->io.direction == KVM_EXIT_IO_OUT
-			    && vcpu->kvm_run->io.port == 0xE9) {
-				char *p = (char *)vcpu->kvm_run;
-				fwrite(p + vcpu->kvm_run->io.data_offset,
-				       vcpu->kvm_run->io.size, 1, stdout);
-				fflush(stdout);
+			if(vcpu->kvm_run->io.direction == KVM_EXIT_IO_OUT) {
+				char *p = (char *)vcpu->kvm_run + vcpu->kvm_run->io.data_offset;
+				switch(vcpu->kvm_run->io.port) {
+				case PORT_PRINT_CHAR: 
+					fwrite(p, vcpu->kvm_run->io.size, 1, stdout);
+					fflush(stdout);
+					break;
+
+				case PORT_PRINT_VALUE:
+					printf("%d", *((uint32_t *)p));
+					fflush(stdout);
+					break;
+				}
 				continue;
 			}