Run a hart lottery on SMP

On systems with SMP multiple harts will try to run the kernel, and they
will appear at random. But in this kernel, in order to keep things
simple, we want to make sure that *only one* hart is running the show,
as it greatly simplifies things on these kinds of systems.

The solution is similar to what Linux does, which is to allow the first
hart to initialize things, but then (and different to what Linux does),
it will infinitely stall all the other harts that arrive at a random
later point in time.

In order to make this more apparent, I have also added a print message
showing which hart is being used to run the whole thing.

Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>

1 files changed, 14 insertions, 1 deletions

diff --git a/kernel/printk.c b/kernel/printk.c
index bd2bcab..1cc68db 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -3,7 +3,7 @@
 #include <fbos/string.h>
 #include <fbos/sbi.h>
 
-void __noreturn __kernel die(const char *const message)
+__kernel __noreturn void die(const char *const message)
 {
 	if (message) {
 		printk(message);
@@ -13,6 +13,19 @@ void __noreturn __kernel die(const char *const message)
 		;
 }
 
+__kernel void print_digit(uint32_t digit)
+{
+	char buffer[2];
+
+	if (digit > 9) {
+		die("We cannot print numbers with two or more digits :D\n");
+	}
+
+	buffer[0] = '0' + digit;
+	buffer[1] = '\0';
+	write(buffer, 2);
+}
+
 __kernel void write(const char *const message, size_t n)
 {
 	struct sbi_ret ret = sbi_ecall2(DBCN_EXT, DBCN_WRITE, n, (unsigned long)message);