Setup the stack for an init task

Bootstrap an init task which holds at least the initial stack that is to
be used when setting up the registers (such as `sp` and `tp`).

In order to guarantee that the stack and the rest of the registers are
set up correctly, this commit also provides a raw implementation of a
`printk` function.

Moreover, this commit also adds an argument that must be passed to
`start_kernel`, which is the pointer to the embedded `fdt` blob. This
argument will be used by later work so to fetch, at least, the base
address for the initial ram disk. This was also used to test that the
stack was working as expected.

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

1 files changed, 7 insertions, 5 deletions

diff --git a/kernel/fbos.ld.S b/kernel/fbos.ld.S
index f288161..f74d90f 100644
--- a/kernel/fbos.ld.S
+++ b/kernel/fbos.ld.S
@@ -3,15 +3,15 @@
 SECTIONS {
 	// Ensure that the image starts at the very exact address SBI expects it to.
 	. = LINK_ADDR;
+	_start = .;
+	. = ALIGN(PAGE_SIZE);
 
 	// You would usually want to separate the head section into its own thing
 	// instead of clumping it into the main `.text` one. Well, I'm no expert on
 	// linker configuration, so patches are welcome :)
 	.text : {
-		// The very first thing has to be the `_start` function, which is where
-		// SBI will jump into. Afterwards comes the rest of `.text.head`.
-		_start = .;
-		*(.text.head)
+		_text = .;
+		*(.head.text)
 
 		// Aligning it to a full page is maybe a bit too much considering how
 		// small `.text.head` really is. I just saw this same thing on the Linux
@@ -23,7 +23,7 @@ SECTIONS {
 		// that large. That is, we put first the very core of the kernel, and
 		// the rest can go wherever.
 		__kernel_text_start = .;
-		*(.text.kernel)
+		*(.kernel.text)
 		__kernel_text_end = .;
 
 		// And the rest.
@@ -49,4 +49,6 @@ SECTIONS {
 	.bss : {
     	*(.bss)
 	}
+
+	_end = .;
 }