read _syscall_debuglog arguments across page boundaries

2 files changed, 28 insertions, 14 deletions

diff --git a/src/init/main.c b/src/init/main.c
index 5615980..89f964f 100644
--- a/src/init/main.c
+++ b/src/init/main.c
@@ -1,13 +1,15 @@
 #include <kernel/syscalls.h>
 
-int main() {
-	_syscall_debuglog("hello from init! ",
-	           sizeof("hello from init! ") - 1);
-
-	_syscall_fork();
+#define STR_64  "This string has exactly 64 characters. It'll be repeated a bunch"
+#define STR_256 STR_64  STR_64  STR_64  STR_64
+#define STR_1K  STR_256 STR_256 STR_256 STR_256
+#define STR_4K  STR_1K  STR_1K  STR_1K  STR_1K
+#define STR_LNG "start " STR_4K STR_4K " finished! "
 
-	_syscall_debuglog("i got forked. ",
-	           sizeof("i got forked. ") - 1);
+int main() {
+	// try to print a string which is longer than a page
+	_syscall_debuglog(STR_LNG,
+	           sizeof(STR_LNG) - 1);
 
 	_syscall_exit("bye from init! ",
 	       sizeof("bye from init! ") - 1);
diff --git a/src/kernel/syscalls.c b/src/kernel/syscalls.c
index 47f8b2b..7234e10 100644
--- a/src/kernel/syscalls.c
+++ b/src/kernel/syscalls.c
@@ -23,15 +23,27 @@ int _syscall_fork() {
 
 int _syscall_debuglog(const char *msg, size_t len) {
 	struct pagedir *pages = process_current->pages;
-	void *phys = pagedir_virt2phys(pages, msg, true, false);
+	size_t remaining = len;
 
-	// page overrun check
-	if (((uintptr_t)msg & PAGE_MASK) + len > PAGE_SIZE)
-		len = PAGE_SIZE - ((uintptr_t)msg & PAGE_MASK);
-	if (((uintptr_t)msg & PAGE_MASK) + len > PAGE_SIZE)
-		panic(); // just in case I made an off by 1 error
+	while (remaining > 0) {
+		/* note: While i'm pretty sure that this should always work, this
+		 * was only tested in cases where the pages were consecutive both in
+		 * virtual and physical memory, which might not always be the case.
+		 * TODO test this */
+
+		void *phys = pagedir_virt2phys(pages, msg, true, false);
+		size_t partial = remaining;
+
+		// don't read past the page
+		if (((uintptr_t)msg & PAGE_MASK) + remaining > PAGE_SIZE)
+			partial = PAGE_SIZE - ((uintptr_t)msg & PAGE_MASK);
+
+		tty_write(phys, partial);
+
+		remaining -= partial;
+		msg       += partial;
+	}
 
-	tty_write(phys, len);
 	return len;
 }