boot: ignore unaddressable RAM areas on i386

We don't support PAE or any other fancy hack to
get past the 4 GB limit on 32-bit, so we have to
clip areas that would fall outside that range

arch/x86/boot/boot.c

@@ -4,10 +4,10 @@
 
 #include <arch/interrupt.h>
 #include <arch/multiboot.h>
+#include <arch/port.h>
 #include <arch/vmparam.h>
 
 #include <gay/cdefs.h>
-#include <gay/config.h>
 #include <gay/kprintf.h>
 #include <gay/mm.h>
 #include <gay/types.h>
@@ -81,7 +81,7 @@ static const char *mmap_type_name(u32 type);
 
 extern int main(int argc, char *argv[]);
 
-__asmlink void _boot(u32 magic, uintptr_t phys_address) /* NOLINT */
+__asmlink void _boot(u32 magic, uintptr_t phys_address)
 {
 	kprintf_set_printer(&fb_kprintf_printer);
 	fb_init(VGA_COLOR_LIGHT_GREY, VGA_COLOR_BLACK);
@@ -142,20 +142,32 @@ static inline int handle_mmap_tag(struct mb2_tag_mmap *tag)
 
 	struct mb2_mmap_entry *entry = &tag->entries[0];
 	while ((void *)entry < (void *)tag + tag->tag.size) {
-		kprintf(" [%p-%p] %s\n",
-			(void *)entry->addr,
-			(void *)entry->addr + entry->len - 1,
+		kprintf(" [0x%016llx-0x%016llx] %s\n",
+			entry->addr,
+			entry->addr + entry->len - 1,
 			mmap_type_name(entry->type));
 
-		if (entry->type == 1 && entry->len > region_len) {
+		usize safe_len;
+#		ifdef __x86_64__
+			safe_len = entry->safe_len;
+#		else
+			if (entry->addr >= (1llu << 32))
+				safe_len = 0; /* we can't handle 64-bit pointers */
+			else if (entry->len > (1llu << 32) - entry->addr)
+				safe_len = (1llu << 32) - entry->addr; /* clip to 32-bit */
+			else
+				safe_len = entry->len;
+#		endif
+
+		if (entry->type == MB2_MEMORY_AVAILABLE && safe_len > region_len) {
 			region = entry->addr;
-			region_len = entry->len;
+			region_len = safe_len;
 		}
 
 		entry = (void *)entry + tag->entry_size;
 	}
 
-	if (region == 0) {
+	if (region == 0 || region_len == 0) {
 		kprintf("No memory available! Aborting.\n");
 		return 1;
 	}
@@ -182,9 +194,9 @@ static void fb_newline(void)
 	fb_col = 0;
 
 	if (fb_line == FB_LINES - 1) {
-		u8 *first_row = (u8 *)cell_at(0, 0);
-		u8 *second_row = (u8 *)cell_at(1, 0);
-		u8 *last_row_end = (u8 *)cell_at(FB_LINES, FB_COLS);
+		void *first_row = (void *)cell_at(0, 0);
+		void *second_row = (void *)cell_at(1, 0);
+		void *last_row_end = (void *)cell_at(FB_LINES, FB_COLS);
 		memmove(first_row, second_row, last_row_end - second_row);
 	} else {
 		fb_line++;
@@ -227,7 +239,7 @@ static void fb_clear(void)
 {
 	for (unsigned int l = 0; l < FB_LINES; l++) {
 		for (unsigned int c = 0; c < FB_COLS; c++) {
-			cell_at(l, c)->c = '\0';
+			cell_at(l, c)->c = ' ';
 			cell_at(l, c)->fg = fb_foreground;
 			cell_at(l, c)->bg = fb_background;
 		}
@@ -241,6 +253,10 @@ static void fb_init(enum vga_color fg, enum vga_color bg)
 	fb_foreground = fg;
 	fb_background = bg;
 
+	/* disable cursor */
+	x86_outb(0x3D4, 0x0A);
+	x86_outb(0x3D5, 0x20);
+
 	fb_clear();
 }
 
@@ -254,13 +270,14 @@ static void print_gay_propaganda(void)
 		VGA_COLOR_BLUE,
 		VGA_COLOR_MAGENTA,
 	};
+	static char line[FB_COLS];
+	memset(line, ' ', FB_COLS);
 
 	enum vga_color bg_before = fb_background;
 	enum vga_color fg_before = fb_foreground;
 	for (int i = 0; i < ARRAY_SIZE(rainbow); i++) {
 		fb_background = rainbow[i];
-		for (int j = 0; j < FB_COLS; j++)
-			fb_write(NULL, " ", 1);
+		fb_write(NULL, line, FB_COLS);
 	}
 	fb_background = bg_before;